DOI: 10.1002/chem.201304207

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& Fluorescence

Synthetic Control of Spectroscopic and Photophysical Properties of Triarylborane Derivatives Having Peripheral Electron-Donating Groups Akitaka Ito,*[a, c] Kazuyoshi Kawanishi,[b] Eri Sakuda,[a, b, d] and Noboru Kitamura*[a, b]

Chem. Eur. J. 2014, 20, 3940 – 3953

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Full Paper Abstract: The spectroscopic and photophysical properties of triarylborane derivatives were controlled by the nature of the triarylborane core (trixylyl- or trianthrylborane) and peripheral electron-donating groups (N,N-diphenylamino or 9H-carbazolyl groups). The triarylborane derivatives with and without the electron-donating groups showed intramolecular charge-transfer absorption/fluorescence transitions between the p orbital of the aryl group (p(aryl)) and the vacant p orbital on the boron atom (p(B), p(aryl)–p(B) CT), and the fluorescence color was tunable from blue to red by the com-

Introduction Highly emissive multicolor chromophores that emit in a broad UV/Vis wavelength region are possible candidates for materials applied to organic light-emitting diodes (OLEDs),[1] and imaging/sensing devices;[2] therefore, their exploitation and development are of primary importance. We have focused on triarylborane derivatives as a promising material.[3] A class of these derivatives possesses both a planar sp2-hybridized structure and the vacant p orbital on the central three-coordinate boron atom (p(B)) in the electronic ground state.[4] Owing to such electronic structures, triarylborane derivatives with relatively large p-electron systems show characteristic absorption and fluorescence that largely differ from those of the aryl group itself. Tri(9-anthryl)borane, a representative compound reported by Yamaguchi et al. in 2000,[5] shows new absorption/fluorescence bands in the visible region in addition to those of anthracene itself. The new absorption/fluorescence bands observed for tri(9-anthryl)borane are ascribed to the intramolecular charge transfer (CT) transitions from the p orbital of the anthryl group, p(aryl), to p(B), p(aryl)–p(B) CT, as demonstrated by solvent dependences of the absorption/fluorescence[6] and electroabsorption/electrofluorescence spectra of the derivative.[7] Owing to such fascinating spectroscopic and photophys[a] Dr. A. Ito, Dr. E. Sakuda, Prof. Dr. N. Kitamura Department of Chemistry Faculty of Science, Hokkaido University Kita-10, Nishi-8, Kita-ku, Sapporo 060-0810 (Japan) Fax: (+ 81) 11-706-4630 E-mail: [email protected] [email protected] [b] K. Kawanishi, Dr. E. Sakuda, Prof. Dr. N. Kitamura Department of Chemical Sciences and Engineering Graduate School of Chemical Sciences and Engineering Hokkaido University Kita-10, Nishi-8, Kita-ku, Sapporo, 060-0810 (Japan) [c] Dr. A. Ito Department of Chemistry Graduate School of Science, Osaka City University 3-3-138, Sugimoto, Sumiyoshi-ku, Osaka 558-8585 (Japan) [d] Dr. E. Sakuda PRESTO (Japan) Science and Technology Agency (JST) 4-1-8, Honcho, Kawaguchi, Saitama 332-0012 (Japan)

bination of peripheral electron-donating groups and a triarylborane core. Detailed electrochemical, spectroscopic, and photophysical studies of the derivatives, including solvent dependences of the spectroscopic and photophysical properties, demonstrated that the HOMO and LUMO of each derivative were determined primarily by the nature of the peripheral electron-donating group and the triarylborane core, respectively. The effects of solvent polarity on the fluorescence quantum yield and lifetime of the derivatives were also tunable by the choice of the triarylborane core.

ical properties, a variety of triarylborane derivatives, including polymers/dendrimers[8] and transition-metal complexes,[9] have been hitherto synthesized for the development of luminescent-,[10] optoelectronic- (OLED/EL, nonlinear optical, and twophoton absorption),[11] and sensing materials,[12] and for other applications.[13] The electron-accepting ability of p(B) will make the excitedstate characteristics of a triarylborane controllable by the introduction of an electron-donating group(s) to the periphery of the aryl group(s) in the triarylborane.[14] One remarkable example is tris{[p-(N,N-dimethylamino)phenylethynyl]duryl}borane (TMAB) having three N,N-dimethylamino groups in the periphery of the tridurylborane core.[15] It is worth emphasizing that TMAB shows an extremely large fluorescence solvatochromic shift from blue to red, owing to the electric dipole moment in the singlet excited state, as large as ~ 60 D (1 D = 1018 esu cm).[16] Such a large excited-state dipole moment is due to the presence of the peripheral electron-donating N,Ndimethylamino groups; for the fluorescent excited state of TMAB, it has been demonstrated that almost one electron is transferred from the N,N-dimethylamino group to p(B).[16] Because introduction of electron-donating groups to the periphery of a triarylborane core brings about large effects on the spectroscopic and excited-state properties of the derivative, as observed for TMAB, further systematic study on a series of derivatives is worth conducting to develop new materials in the relevant research fields. Herein, we report the synthesis and excited-state properties of a series of triarylboranes having electron-donating groups, 1 a–c and 2 a–c, whose structures are shown in Scheme 1. To control the spectroscopic and photophysical properties of the triarylborane, we employed trixylylborane (1 a–c) and trianthrylborane units (2 a–c) as relatively small and large p-electron systems, respectively, and introduced three electron-donating 9H-carbazolyl (1 b, 2 b) or N,Ndiphenylamino groups (1 c, 2 c) to the periphery of the triarylborane core. Tri(2-m-xylyl)borane (1 a) and tri(9-anthryl)borane (2 a) were also studied as references. We report the spectroscopic and photophysical properties of these six triarylborane derivatives in special references to the solvent-polarity dependences of these characteristics.

Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201304207. Chem. Eur. J. 2014, 20, 3940 – 3953

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Scheme 1. Molecular structures of 1 a–c and 2 a–c.

Figure 1. Cyclic (solid curves) and differential pulse voltammograms (broken curves) of 1 a–c and 2 a–c. Dichloromethane and THF were used as solvents in the positive and negative potential regions, respectively.

Results and Discussion Electrochemical properties To confirm the introduction of the electron-donating 9H-carbazolyl (1 b, 2 b) or N,N-diphenylamino groups (1 c, 2 c) into a trixylylborane (1 a–c) or trianthrylborane core (2 a–c), we studied the redox potentials of the derivatives. Figure 1 shows the cyclic (CV) and differential pulse voltammograms (DPV) of the derivatives. The voltammograms in the positive and negative potential regions were measured separately by employing dichloromethane and tetrahydrofuran (THF), respectively, as solvents. The redox potentials determined are summarized in Table 1. It is worth noting that 1 b and 2 b show irreversible oxTable 1. Redox potentials of 1 a–c and 2 a–c in dichloromethane and THF (0.1 m TBAPF6) in the positive and negative potential regions, respectively. Derivative red 1a 1b 1c 2a 2b 2c

ox 1 [a]

N.D. 1.94 N.D.[a] 1.45 1.25 1.26

1.79 1.19 0.92 1.23 1.24 0.93

E1/2 [V] vs. SCE ox 2 ox 3 1.30 1.05 1.39 1.36 1.04

1.75 1.17 1.57 1.60 1.17

[a] Potential more negative than 2.0 V vs. SCE.

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ox 4

ox 5

1.76

1.52

1.72

idation waves at ca. + 0.5 and + 0.9 V (versus SCE), respectively, and that these waves are due to the oligomerization of the carbazole groups, as reported for 1 b by Lambert et al.[17] Because this behavior is not relevant to the investigation herein, the data on these irreversible oxidation waves, as observed for 1 b and 2 b, are not included in Table 1 and this behavior will not be commented on further. The reduction waves (E1/2(red)) observed for 1 b and 2 a– c are ascribed to those of the triarylborane cores; the trixylylborane and trianthrylborane cores exhibited E1/2(red) at 1.94 and in the range, 1.25–1.45 V, respectively. On the other hand, 1 a showed an oxidation wave (E1/2(ox 1)) at + 1.79 V, while 2 a exhibited three consecutive oxidation waves at E1/2(ox 1, ox 2, ox 3) = + 1.23, + 1.39, and + 1.57 V, corresponding to the oxidation of the three anthryl groups. The potentials of the first three oxidation waves of 1 c (E1/2(ox 1, ox 2, ox 3) = + 0.92, + 1.05, and + 1.17 V) were almost comparable with those of 2 c (E1/2(ox 1, ox 2, ox 3) = + 0.93, + 1.04, and + 1.17 V), indicating the sequential oxidation of the N,N-diphenylamino groups in 1 c similar to that of the anthryl groups in 2 a. Because the oxidation potentials observed for 1 b (E1/2(ox 3) = + 1.75 V) and 1 c (E1/2(ox 4) = + 1.76 V) were very similar to that of 1 a (E1/2(ox 1) = + 1.79 V), the potentials correspond to the

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Full Paper oxidation of the xylyl group. On the other hand, the oxidation behavior of 2 b was somewhat different from those of other derivatives and the E1/2(ox 1, ox 2, ox 3) values of + 1.24, + 1.36, and + 1.60 V were not in accord with the oxidation potentials of the 9H-carbazolyl groups in 1 b (+ 1.19 and + 1.30 V), but similar to those of the anthryl groups in 2 a (+ 1.23, + 1.39, and + 1.57 V). Because our DFT calculations (see below) indicate electron delocalization among the anthryl and carbazolyl groups in the highest-energy occupied molecular orbital (HOMO) in 2 b, the oxidation potentials observed for 2 b would be the admixture of those of the anthryl and carbazolyl groups. Although the nature of the E1/2(ox 1) value of 2 b is ambiguous, as described above, the negative shift of E1/2(ox 1) in the sequence 1 b (+ 1.19 V) > 1 c (+ 0.92 V) demonstrates clearly that the electron-donating ability of the N,N-diphenylamino group is higher than that of the 9H-carbazolyl group. Furthermore, the E1/2(red) value is in the range 1.25–2.0 V, depending on the nature of the triarylborane core. Because E1/2(ox 1) and E1/2(red) correspond to the HOMO and lowest-energy unoccupied molecular orbital (LUMO) energies, respectively, the absorption and fluorescence characteristics of the derivatives

would vary by the nature of both the electron-donating group and the triarylborane core, a dependence that will be described in detail in the following sections. Absorption and fluorescence spectra in THF We studied the absorption and fluorescence spectra of the six derivatives in a series of solvents; the spectroscopic properties of the derivatives are summarized in Tables 2 and 3. Typically, the absorption and fluorescence spectra of the derivatives in THF are shown in Figure 2. All of the derivatives exhibited several absorption bands in the range 17 000–37 000 cm1 (270– 590 nm) and the spectra were characterized by broad lowestenergy and relatively structured higher-energy bands. The higher-energy absorption band observed for each derivative can be ascribed to the p–p* transition of the aryl group as judged by the close similarities of the absorption energy and spectral band shapes with those of the aryl group itself; the spectral comparison between 1 b, 2 a, 2 c, and the relevant model compounds can be found in the Supporting Information, Figures S1–S3. To elucidate the nature of the broad lowest-energy absorption bands of 1 b, 2 a, and 2 c, we studied

Table 2. Solvent parameters and spectroscopic properties of 1 a–c.

Ds[a]

Solvent Parameters n[a] f(Ds,n)[b] g(n)[b]

1.8799 2.023 2.3779 4.806 6.02 7.58 8.93 10.36 20.7 37.5 46.68

1.37226 1.42623 1.49413 1.44293 1.36979 1.40496 1.42115 1.4421 1.35596 1.34411 1.4773

Solvent

n-hexane cyclohexane toluene chloroform ethyl acetate THF dichloromethane 1,2-dichloroethane acetone CH3CN DMSO

0.00078 0.00259 0.03041 0.37211 0.49026 0.55004 0.59155 0.62301 0.79124 0.86305 0.84102

0.25328 0.28920 0.33358 0.30021 0.25163 0.27511 0.28584 0.29966 0.24234 0.23435 0.32267

1a na (e) [cm1 (103 m1 cm1)]

nf [cm1]

1b na (e) [cm1 (103 m1 cm1)]

nf [cm1]

1c na (e) [cm1 (103 m1 cm1)]

nf [cm1]

31000 (11.3) 30700 (9.8) 30700 (11.3) 30600 (11.3) 30700 (10.3) 30800 (11.9) 30700 (10.5) 30600 (10.3) competing[c] 30700 (9.6) 30500 (8.4)

27400 27300 27200 27000 27000 27000 26900 26900 26500 26700 26500

26100 26000 26300 26700 26900 26700 26900 26900 27100 27200 26900

24400 24300 23300 22900 21900 21700 22100 22000 21000 20600 20300

24500 (64.4) 24400 (58.6) 24400 (51.0) 24600 (49.4) 24700 (49.5) 24500 (53.9) 24600 (47.4) 24500 (45.8) 24700 (47.4) insoluble[d] 24500 (47.1)

22800 22700 22000 21300 20700 20600 20500 20300 19600 19100 19000

(36.7) (36.1) (31.5) (29.3) (29.9) (28.2) (29.4) (31.0) (33.6) (N.D.)[d] (27.2)

[a] Data taken from ref. [34]. [b] Calculated by using Equations (1). [c] Could not be determined due to superposition of absorption by solvent itself. [d] Could not be determined due to the low solubility of the derivative.

Table 3. Spectroscopic properties of 2 a–c. Solvent

n-hexane cyclohexane toluene chloroform ethyl acetate THF dichloromethane 1,2-dichloroethane acetone CH3CN DMSO

2a na (e) [cm1 (103 m1 cm1)]

nf [cm1]

2b na (e) [cm1 (103 m1 cm1)]

21400 (26.7) 21300 (25.2) 21100 (23.2) 21200 (20.3) 21300 (20.9) 21300 (21.3) 21100 (19.6) 21200 (20.3) 21300 (20.2) 21300 (21.2) 21100 (21.0)

19500 19300 19000 18600 18700 18500 18300 18200 18000 17800 17600

20500 20500 20300 20500 20500 20500 20400 20300 20500 20500 20000

(N.D.)[a] (N.D.)[a] (N.D.)[a] (N.D.)[a] (N.D.)[a] (25.2) (N.D.)[a] (N.D.)[a] (N.D.)[a] (N.D.)[a] (N.D.)[a]

nf [cm1]

2c na (e) [cm1 (103 m1 cm1)]

nf [cm1]

18500 18400 18000 17800 17700 17600 17600 17500 17300 17000 decomp.[b]

19400 (19.4) 19300 (36.0) 19100 (32.7) 19300 (28.9) 19300 (32.2) 19300 (32.5) 19300 (31.7) 19200 (31.5) 19300 (31.5) insoluble[c] 19000 (27.2)

17400 17400 16800 16500 16200 16100 15800 15800 15500 15200 14900

[a] Could not be determined due to the low isolation yield of the derivative. [b] Could not be determined due to decomposition of the derivative. [c] Could not be determined due to the low solubility of the derivative.

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Figure 2. Absorption (broken curves) and fluorescence spectra (solid curves) of 1 a–c (upper panel) and 2 a–c (lower panel) in THF. The colors correspond to those indicated in Figure 1.

the effects of a fluoride ion (derived from tetra-n-butylammonium fluoride, TBAF) on the absorption spectra (see the Supporting Information, Figures S4–S6). A fluoride ion is known to act as a Lewis base for p(B) and coordinates with the boron atom in a triarylborane derivative. As seen in Figures S4–S6 in the Supporting Information, the lowest-energy absorption bands of 1 b, 2 a, and 2 c in THF with energies of 26 700, 21 300, and 19 300 cm1 (375, 469, and 518 nm), respectively, were attenuated upon addition of TBAF and the absorption spectra in the presence of sufficient amounts of TBAF agreed very well with those of the relevant model compounds, 9H-(2-m-xylyl)carbazole, anthracene, and 9-N,N-diphenylaminoanthracene. Similar TBAF effects on the absorption spectra of 1 a, 1 c, and 2 b were also confirmed. The results demonstrate that the lowestenergy absorption bands of these triarylboranes are strongly influenced by p(B) and we confidently assign the bands to p(aryl)–p(B) CT transitions. The absorption maximum energy of the p(aryl)–p(B) CT band (na) observed for 1 c or 1 b, 24 500 or 26 700 cm1 (408 or 375 nm), respectively, in THF, the compound having N,N-diphenylamino or 9H-carbazolyl groups, respectively, is lower than that of 1 a (30 800 cm1 (325 nm)). The molar absorption coefficients of the bands (e) for 1 c and 1 b are also larger than that of 1 a in THF, the values being 53 900, 28 200, and 11 900 m1 cm1, respectively. Furthermore, 1 c or 2 c, which has N,N-diphenylamino groups, showed more intense (that is, larger e value) and lower-energy absorption compared to the Chem. Eur. J. 2014, 20, 3940 – 3953

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band observed for the carbazolyl-type derivative 1 b or 2 b (see also Tables 2 and 3). These characteristics are due to the stronger electron-donating ability of the N,N-diphenylamino group in 1 c or 2 c relative to that of the 9H-carbazolyl group in 1 b or 2 b, thus agreeing very well with the oxidation potential of the N,N-diphenylamino or 9H-carbazolyl group, as discussed above. The lower-energy shifts of the p(aryl)–p(B) CT absorption bands of the 9H-carbazolyl- and N,N-diphenylamino-type derivatives compared to that of 1 a or 2 a is due to destabilization of the ground state by the presence of the lone-pair electrons on the nitrogen atoms as well as stabilization of the excited-states of 1 b, 1 c, 2 b, or 2 c (a more detailed discussion on the basis of the solvent polarity dependences of the absorption and fluorescence spectra of the derivatives is given below). The increase in the e value of the p(aryl)–p(B) CT band of the 9H-carbazolyl- (1 b, 2 b) or N,N-diphenylamino-type derivative (1 c, 2 c) compared to that of 1 a or 2 a is due essentially to the presence of the electron-donating groups and, thus, to charge transfer from the peripheral electron-donating group to the vacant p orbital on the boron atom. All of the derivatives showed broad and structureless fluorescence spectra, which were completely different from those of the relevant model compounds, as shown in Figure 2 and Figures S1–S3 in the Supporting Information. Fluoride-addition experiments, as illustrated in Figures S4–S6 in the Supporting Information, have revealed that the fluorescence observed for the derivatives comes from the p(aryl)–p(B) CT excited states. In THF, the fluorescence maximum energies (nf) of the 9H-carbazolyl- (1 b and 2 b: 21 700 and 17 600 cm1 (461 and 568 nm), respectively) and N,N-diphenylamino-type derivatives (1 c and 2 c: 20 600 and 16 100 cm1 (485 and 621 nm), respectively) were much lower than that of the relevant parent molecule (1 a or 2 a: 27 000 and 18 500 cm1 (370 and 541 nm), respectively) without an electron-donating group; see also Tables 2 and 3. Such behaviors are quite similar to those for the p(aryl)–p(B) CT absorption band and will be explained by destabilization and stabilization of the ground- and excitedstate energies, respectively, and the redox potential of the derivative. The fluorescence energies of the derivatives in THF within the range 16 100–27 000 cm1 (370–621 nm) demonstrate control of the fluorescence energy in the visible region by the nature of the electron-donating substituents in a trixylylborane- or trianthrylborane-core unit. Detailed photophysical properties of the derivatives will be discussed in sections below. Time-dependent density-functional-theory (TD-DFT) calculations To investigate the electronic structures in the ground and excited states of the six derivatives, we conducted TD-DFT calculations. The optimized molecular structures of the derivatives are shown in Figure S7 in the Supporting Information. All the derivatives possess planar BC3 core structures; the results are indicative of no significant effects of the triarylborane core and peripheral electron-donating groups on the ground-state geometries of the derivatives. The details of the five lowest-energy

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Figure 3. Molecular-orbital contours (0.03 e 3) of 1 a–c and 2 a–c in HOMO (bottom) and LUMO (top) obtained by DFT calculations.

absorption transitions of the derivatives are summarized in Tables S1–S6 in the Supporting Information. The lowest-energy absorption transition in each derivative is best characterized by a transition from the HOMO to the LUMO. The molecularorbital contours of the derivatives in the HOMO and LUMO levels are shown in Figure 3. In the LUMO, the electron is localized primarily on the vacant p orbital on the boron atom, irrespective of the derivative; however, the HOMO distributes in different fashions among the six derivatives. The HOMO electron in 1 a or 2 a without an electron-donating group, distributes among the three p orbitals of the aryl groups. In the case of 1 b, 1 c, or 2 c, on the other hand, the electron resides on the electron-donating groups whereas that in 2 b almost delocalizes over the one carbazolyl–anthracene unit. The results on 2 b suggest mixing of the p orbitals of the anthryl and carbazolyl groups, thus agreeing very well with the results of the electrochemical measurements described above. These results demonstrate that the introduction of the three electron-donating groups to the triarylborane core greatly influences the electronic structures of the derivative. The decrease in the calculated HOMO–LUMO transition energy in the order 1 a > 1 b > 1 c or 2 a > 2 b > 2 c agrees very well with the electron-donating ability of the peripheral group (E1/2(ox 1): 1 b (+ 1.19 V) > 1 c (+ 0.92 V) or 2 b (+ 1.24 V) > 2 c (+ 0.93 V)) and shows a quite good linear relationship with the experimentally observed na values in THF, as shown in Figure S8 in the Supporting Information. The slope value of 1.11 between theoretical and experimental absorption energies supports that the calculations successfully reproduce the experimental observations because TD-DFT calculations are known to estimate the transition energy smaller than experimental value by 10 %.[18] The calculated oscillator strength (f(calculated)) of the lowest-energy absorption transition (Tables S1–S6 in the Supporting Information) also relates proportionally to the molar absorption coefficient of the p(aryl)– p(B) CT band in THF (Figure S8 in the Supporting Information). These results indicate that the introduction of electron-donating groups into the triarylborane core should influence largely Chem. Eur. J. 2014, 20, 3940 – 3953

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the spectroscopic/photophysical properties and electronic structures of the derivatives. Solvent dependences of spectroscopic and photophysical properties We studied solvent dependences of the spectroscopic and photophysical properties of the derivatives to evaluate the roles of the peripheral electron-donating group in the groundand excited-state characteristics. Figure 4 shows the absorption and fluorescence spectra of the derivatives in a series of the solvents, and their spectroscopic properties are summarized in Tables 2 and 3, together with the static dielectric constants (Ds) and refractive indices (n) of the solvents used. The trixylylborane- (1 a–c) and trianthrylborane-type derivatives (2 a–c) showed opposite solvent polarity effects on the p(aryl)–p(B) CT absorption band. The p(aryl)–p(B) CT absorption bands of 2 a–c showed bathochromic shifts with an increase in the solvent polarity. Such solvent effects are often observed for an intramolecular CT-type compound owing to stabilization of the charge-separated Franck–Condon excited-state energy. In contrast, 1 a–c showed hypsochromic shifts of the p(aryl)–p(B) CT absorption bands with an increase in Ds, suggesting larger stabilization of the ground-state energy relative to the stabilization energy in the excited state. A homoleptic triarylborane in the ground state generally possesses D3-symmetry and the highly symmetric structure in the ground state would not be affected largely by a solvent. Therefore, the solvent-polarity-induced hypsochromic shifts of the CT absorption bands of 1 a– c will be due to symmetry-breaking structures in the ground states. While the solvent polarity effects on the p(aryl)–p(B) CT absorption band were dependent on the nature of a triarylborane core, the fluorescence spectra of the derivatives showed similar solvent-polarity dependences. The fluorescence maximum energies of the derivatives (nf) shifted to the lower energy (that is, longer wavelength) with an increase in the solvent polarity. Such solvent effects have been sometimes observed for an intramolecular CT-type compound and are due

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Figure 4. Solvent dependences of the absorption (broken curves) and fluorescence spectra (solid curves) of 1 a–c and 2 a–c. The fluorescence intensities are normalized to those at the maximum energies. The vertical axes of the absorption spectra of 1 a–c, 2 a, and 2 c represent the molar absorption coefficients, and absorbance of 2 b is normalized to those at the maximum energies of the p(aryl)–p(B) CT bands.

to stabilization of the fluorescent CT excited-state energy. In the present case, the solvatochromic shift of nf from n-hexane to dimethyl sulfoxide (DMSO), Dnf, was dependent on the nature of the electron-donating groups (see Tables 2 and 3). In practice, the Dnf values of 1 b, 1 c, and 2 c were 4100, 3800, and 2500 cm1, respectively, thus showing larger solvent polarity shifts than that of the parent derivative, 1 a or 2 a (1100 or 1900 cm1, respectively). The results indicate that the derivatives having the peripheral electron-donating groups possess larger electric dipole moments in the excited states and their excited states are stabilized in energy largely compared to the derivatives without an electron-donating group. One exceptional case was 2 b possessing electron-donating 9H-carbazolyl groups and 2 b showed a comparable fluorescence shift to 2 a, Dnf = 1500 cm1 (from n-hexane to CH3CN). It will be due to electron delocalization among the carbazolyl and anthryl groups in the ground state of 2 b as described above. To investigate further the molecular and electronic structures of 1 a–c and 2 a–c, we evaluated the ground- (mg) and excitedstate dipole moments (me) of the derivatives. The mg and me values of a molecule can be determined by the solvent-polarity dependences of the absorption and fluorescence spectra on the basis of the simple quantum-mechanical second-order perturbation theory by Kawski et al. by using the following solvent polarity parameters, f(Ds,n) and g(n),[19]

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f ðDs ; nÞ ¼

  2n2 þ 1 Ds  1 n2  1  n2 þ 2 Ds þ 2 n2 þ 2

  3 n4  1 gðnÞ ¼ 2 ðn2 þ 2Þ2

ð1aÞ

ð1bÞ

where the terms involving Ds and n imply the contributions of the dipole orientation and electronic polarizability of a solvent molecule, respectively, to solvent-induced stabilization of the ground- and excited-state energies of a molecule concerned. The f(Ds,n) and g(n) values used in the present study are included in Table 2. Furthermore, it has been known that the (nanf) and (na + nf) values should correlate linearly with the solvent parameters as given in Equations (2a) and (2b), respectively: na nf ¼ m1 f ðDs ,nÞ þ constant

ð2aÞ

na þ nf ¼ m2 ½f ðDs ,nÞ þ 2gðnÞ þ constant

ð2bÞ

where m1 and m2 are the slope values of the relations in Equations (2 a) and (2 b), respectively. The mg and me values can be then evaluated by Equations (3): m  m1 mg ¼ 2 2

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Full Paper (mg = 0.36–0.80 D), 1 a–c showed the relatively large (1.7 D for 1 a) and/or negative dipole moments in the ground states (2.9 or 0.51 D for 1 b or 1 c, respectively) compared to 2 a–c. The results for 1 b and 1 c suggest non-symmetrical ground-state structures of the derivatives possessing the trixylylborane-core unit and are consistent with the Figure 5. Solvent-parameter dependences of the spectroscopic properties of 1 a–c and 2 a–c. The colors corresolvent dependences of the abspond to those indicated in Figure 1 and the data are taken from Tables 2 and 3. Solid lines correspond to the sorption spectra (hypsochromic linear regression based on Equations (2). solvent polarity shift). On the other hand, the excited-state sffiffiffiffiffiffiffiffiffiffi dipole moment, me, was significantly influenced by the introm2 þ m1 hca3O ð3bÞ me ¼ duction of the electron-donating groups to the triarylborane 2 2m1 core. In practice, 1 b, 1 c, and 2 c in the excited states possess large and comparable dipole moments with me = 11—13 D, inwhere h, c, and aO are the Planck’s constant, the speed of light, dicative of charge transfer from the peripheral electron-donatand the Onsager radius of a molecule, respectively. As shown ing group(s) to the vacant p orbital on the boron atom. Howin Figure 5, the solvent dependences of the (nanf) and (na + nf) values of 2 a (8.0 D) and 2 b (8.5 D) were somewhat ever, the m e values followed Equations (2) (correlation coefficient > 0.93). smaller than those of other derivatives and, in particular, the The slope values of the plots in Figure 5 and the mg/me values electron-donating 9H-carbazolyl groups in 2 b played a minor of each derivative calculated by Equations (3) are summarized . Because the oxidation potentials of the role in determining m e in Table 4, together with the aO values predicted from the anthryl and carbazolyl groups in 2 b comparable to that of 2 a ground-state geometries by DFT calculations. The minus sign are very close to each other and the p orbitals of the anthryl of mg represents the dipole moment with the reverse vector diand carbazolyl group are mixed, as suggested by the TD-DFT rection from that of me. While the ground-state dipole mocalculations described above, the m value of 2 b will be the e ments of 2 a–c were almost comparable with one another reasonable consequence. Solvent dependences of the photophysical properties of the derivatives were also evaluated except for those of 1 a, which Table 4. Solvent-dependent parameters (m1 and m2) and ground-/excitcould not be excited by the present experimental setup ed-state electric dipole moments of 1 a–c and 2 a–c. (405 nm laser pulses). The fluorescence decay profiles of the m1 m2 mg me Derivative aO derivatives shown in Figures S9–S13 in the Supporting Infor1 1 [] [cm ] [cm ] [D] [D] mation can be analyzed by single-exponential functions, and 1a 5.95 600 1180 + 1.7 5.3 the fluorescence quantum yields (Ff) and lifetimes (tf) deter1b 7.35 5190 3100 2.9 11 mined are summarized in Tables 5 and 6, together with the 1c 7.73 4000 3710 0.51 13 2a 6.76 1700 2070 + 0.80 8.0 fluorescence (kf) and nonradiative decay rate constants (kd) cal2b 7.91 1340 1460 + 0.36 8.5 culated by the equations, Ff = kf/(kf+kd) and tf = 1/(kf+kd), 2c 7.92 2310 2630 + 0.73 11 where kd is the sum of the rate constants of internal conver-

Table 5. Solvent dependences of the photophysical properties of 1 b and 1 c. 1b

Solvent

n-hexane cyclohexane toluene chloroform ethyl acetate THF dichloromethane 1,2-dichloroethane acetone CH3CN DMSO

1c

Ff

tf [ns]

kf [107 s1]

kd [107 s1]

Ff

tf [ns]

kf [107 s1]

kd [107 s1]

0.53 0.58 0.58 0.70 0.60 0.95 0.61 0.69 0.90 0.94 0.82

2.1 1.9 2.6 3.2 5.6 6.0 4.9 5.0 9.2 11 10

25 30 22 22 11 16 12 14 9.8 8.6 8.0

23 22 16 9.3 7.2 0.77 8.0 6.2 1.1 0.55 1.8

0.39 0.38 0.36 0.48 0.45 0.53 0.51 0.45 0.53 0.52 0.66

2.0 2.1 2.1 3.0 4.5 4.4 4.8 5.0 7.7 10 8.7

20 18 17 16 10 12 11 8.9 6.9 5.2 7.6

31 29 30 17 12 11 10 11 6.1 4.7 3.9

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Full Paper Table 6. Solvent dependences of the photophysical properties of 2 a–c.

Ff

tf [ns]

2a kf [107 s1]

kd [107 s1]

Ff

tf [ns]

kf [107 s1]

kd [107 s1]

Ff

tf [ns]

kf [107 s1]

kd [107 s1]

0.47 0.53 0.21 0.081 0.075 0.093 0.045 0.037 0.024 0.016 0.022

11 12 7.2 3.2 3.5 4.3 2.3 1.8 1.6 1.1 1.3

4.2 4.5 2.9 2.5 2.1 2.2 2.0 2.1 1.5 1.5 1.7

4.8 4.0 11 29 26 21 42 54 61 89 75

0.39 0.50 0.17 0.12 0.062 0.093 0.059 0.056 0.037 decomp.[a] decomp.[a]

9.4 10 5.9 4.0 2.6 3.9 2.5 2.1 1.7 decomp.[a] decomp.[a]

4.2 5.0 2.9 3.0 2.4 2.4 2.4 2.7 2.2

6.5 5.0 14 22 36 23 38 45 57

0.38 0.45 0.23 0.070 0.047 0.069 0.019 0.028 0.012 0.010 0.084

7.1 8.1 4.7 2.2 1.7 1.9 1.0 1.0 0.78 decomp.[a] decomp.[a]

5.3 5.6 4.9 3.1 2.8 3.6 1.9 2.8 1.5

8.8 6.7 16 42 58 48 98 98 127

Solvent

n-hexane cyclohexane toluene chloroform ethyl acetate THF dichloromethane 1,2-dichloroethane acetone CH3CN DMSO

2b

2c

[a] Could not be determined due to decomposition of the derivative.

sion to the ground state and intersystem crossing to the excited triplet state. All of the derivatives showed relatively intense fluorescence, Ff > 0.1 for 1 b–c in all of the solvents studied and 2 a–c in less polar solvents than toluene. As one of the important findings, 1 b–c and 2 a–c exhibited different trends of the solvent polarity effects on Ff and tf. With an increase in the solvent polarity, the Ff and tf values of 1 b–c having the trixylylborane-core unit increased (for example, Ff = 0.39 and tf = 2.0 ns in n-hexane, Ff = 0.53 and tf = 7.7 ns in acetone for 1 c), while those of 2 a–c with the trianthrylborane core remarkably decreased (for example, Ff = 0.38 and tf = 7.1 ns in n-hexane, Ff = 0.012 and tf = 0.78 ns in acetone for 2 c). It has been known that the tf and Ff values of a CT-type compound in general decrease with an increase in Ds because the singlet excited-state energy is lowered in a high-polarity solvent, thus giving rise to fast nonradiative decay to the ground state, as predicted by the energy-gap (nf) law of a nonradiative-decay rate constant (kd): lnkd = a  nf + constant.[20] In practice, energy-gap dependences of kd have been reported for various organic compounds and transitionmetal complexes.[21] Therefore, the solvent dependences of the photophysical properties observed for 1 b–c are quite unusual as expected from those of ordinary organic compounds. It is worth emphasizing here that such anomalous solvent effects on Ff and tf (and, thus, kd) are neither fortuitous nor due to our experimental error because similar solvent effects have been also observed for tris{[p-(N,N-dimethylamino)phenylethynyl]duryl}borane (TMAB) by the present authors[16] as well as for 1 b by Lambert et al.[17] Figure 6 shows the energy-gap (nf) dependences of lnkd observed for the derivatives. As clearly seen in the figure, the lnkd values of 2 a–c linearly decrease with an increase in nf, while those of 1 b–c exhibit opposite trends to what is observed for 2 a–c. In the case of 2 a–c, the Ff and tf values are determined primarily by kd ; kf < kd, except for the values of 2 a in n-hexane and cyclohexane. In a polar solvent, the CT excited states of these derivatives are stabilized in energy and undergo fast nonradiative decay to the ground state as in the case of a typical CT excited state. In the case of 1 b and 1 c, on the other hand, the kd values decrease by ~ 10-fold on going from nChem. Eur. J. 2014, 20, 3940 – 3953

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Figure 6. Energy gap plots for 1 a–c and 2 a–c. The colors correspond to those indicated in Figure 1 and the data are taken from Tables 2, 3, 5, and 6.

hexane to DMSO and the kf/kd ratios become larger with an increase in the solvent polarity, as seen in Table 5. Therefore, the Ff and tf values of 1 b and 1 c become larger and longer, respectively, with an increase in Ds. The nonradiative reverse-CT process from the excited CT state of 1 b or 1 c having me of + 11 or + 13 D, respectively, to the ground state with the opposite dipole moment (mg = 2.9 or 0.51 D, respectively) should accompany both relatively large structural change and solvent reorganization energy and, thus, these factors will impede the nonradiative decay process, showing reverse energy-gap dependence of lnkd. Such ground- and excitedstate characteristics will be the origin of the reverse energygap dependence of kd observed for 1 b and 1 c. We are currently studying more detailed solvent dependences of the photophysical properties of 1 b–c, which will be reported in a separate publication.

Conclusion The present study demonstrated that the spectroscopic and photophysical properties of a triarylborane derivative were controllable by the nature of a triarylborane core (tri(2-m-xylyl)borane or tri(9-anthryl)borane) and peripheral electron-donat-

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Full Paper ing groups (N,N-diphenylamino or 9H-carbazolyl groups). All of the six derivatives showed the p(aryl)–p(B) CT absorption/fluorescence, and the fluorescence wavelength was successfully tuned over the visible region by the combination of the peripheral electron-donating groups and a triarylborane core. The detailed electrochemical, spectroscopic and photophysical measurements on the derivatives provided several important insights into the control of the spectroscopic and excited-state characteristics.

Introduction of peripheral electron-donating groups to a triarylborane core The HOMO and LUMO energies of triarylborane are determined primarily by the nature of the peripheral electron-donating group and a triarylborane core, respectively. As a result, an introduction of a stronger electron-donating group(s) to a given triarylborane core makes the fluorescent excited state lower in energy and, thus, the fluorescence energy of the derivative is controllable. Distributions of the HOMO electron from the electron-donating groups to p(B) resulted in a relatively large excited-state electric dipole moment of the derivative (me = 8.5—13 D). Owing to such me values, the derivatives showed large fluorescence solvatochromic shifts. Furthermore, the change in the dipole moment upon photoexcitation of the derivative (that is, memg) brought about enhancement of the molar absorption coefficient of the p(aryl)–p(B) CT absorption band. These are the effects of the electron-donating groups introduced to the periphery of a triarylborane core and an appropriate choice of the nature of an electron-donating group(s) would lead to synthetic tuning of both spectroscopic and excited-state properties of the derivatives.

Role of a triarylborane core in the spectroscopic/ photophysical properties The trixylylborane-core derivatives showed hypsochromic shifts of the p(aryl)–p(B) CT absorption bands with an increase in the solvent polarity probably owing to the symmetry-breaking structures in the ground states, while the CT absorption bands of the trianthrylborane-core derivatives exhibited opposite (bathochromic) solvent-polarity effects. We suppose that these results originate from the structural rigidity of the derivative in the ground state and the trixylylborane-core derivatives having less rigid/crowded structures, compared to the trianthrylborane-core derivatives, deviate from D3 symmetry in the ground states. This might be one of the possible reasons for different solvent polarity responses to the Ff and tf values between the trixylylborane- and trianthrylborane-core derivatives, and these photophysical properties can be also tuned by a choice of a triarylborane core. These insights obtained in this study will greatly contribute to molecular design toward future triarylborane-based materials, devices, and other fascinating systems. Chem. Eur. J. 2014, 20, 3940 – 3953

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Experimental Section Chemicals Tris[2-{5-(9H-carbazolyl)-m-xylyl}]borane (1 b) was synthesized according to the literature[17] and identified by IR, 1H NMR, and elemental analysis.[22] Derivative 2 a was the same sample with that reported earlier.[6–7, 23] Acetonitrile (Wako Pure Chemical Industries) for spectroscopic measurements was distilled prior to the use.[24] Other spectroscopic-grade solvents purchased from Wako Pure Chemical Industries, Kanto Chemical Company, or Dojindo Molecular Technologies were used without further purification. As the solvents for electrochemical measurements, anhydrous CH2Cl2 and THF (Wako Pure Chemical Industries) were used as supplied.

Synthesis Derivatives 1 c, 2 b, and 2 c were synthesized through the coppercatalyzed coupling reaction of a xylene or anthracene derivative with diphenylamine or carbazole and subsequent reaction of the product with n-butyllithium (nBuLi) or tert-butyllithium (tBuLi). Although 1 a has been reported to be synthesized by a Grignard reaction,[25] it has been successfully synthesized by using tBuLi. Synthetic details are described below. The reagents for synthesis, purchased from Wako Pure Chemical Industries, Tokyo Chemical Industry Company, Kanto Chemical Company. or Fluorochem, were used as supplied. The synthesized compounds were purified by column chromatography (Merck silica gel 60, particle size: 0.063–0.020 mm) or Recycling Preparative HPLC (Japan Analytical Industry Company, LC-9201) with a JAIGEL-1H gel-permeation chromatography (GPC) column equipped with UV3740 UV/Vis and RI-50s RI detectors. Thin-layer chromatography was conducted by using Merck silica gel 60 F245 aluminum sheets and the sample spots were visualized by a UVP UVGL-25 compact UV lamp. Electron ionization (EI-MS) and electrospray ionization mass spectrometry (ESI-MS) were performed by direct injection into the mass detector of a Shimadzu GCMS-QP5000 system and a Waters micromass ZQ detector, respectively. Melting points of the compounds were determined using a Yanaco MP-500D or SANSYO Meltingpoint SMP-300 apparatus. 1H NMR spectra in CDCl3 or CD2Cl2 (both from Cambridge Isotope Laboratories) were recorded on a JEOL LME-EX270 FT-NMR system (270 MHz). The chemical shifts of the spectra were given in ppm with tetramethylsilane as an internal standard (0.00 ppm). IR spectra were recorded on a Shimadzu FTIR-8300 spectrometer. Elemental analyses were conducted in the Instrumental Analysis Division, Equipment Management Center, Creative Research Institution, Hokkaido University. Spectroscopic and photophysical purities of 1 b–1 c and 2 a–2 c were confirmed by single-exponential fluorescence decays in toluene (see Figures S9–S12 in the Supporting Information). Synthesis of tri(2-m-xylyl)borane (1 a): An oven-dried Schlenk tube was evacuated and filled subsequently with argon gas. Into the vessel were added 2-bromo-m-xylene (0.86 mL, 6.5 mmol) and dry diethyl ether (11 mL) and, then, the mixture was cooled to 78 8C in an acetone/dry ice bath for 30 min. tBuLi (1.57 m in npentane, 9.5 mL, 15 mmol) was added dropwise to the reaction mixture at 78 8C. After stirring at 78 8C for 30 min, the mixture was allowed to warm to 0 8C and, then, stirred for further 30 min. Boron trifluoride diethyl etherate (0.26 mL, 2.1 mmol) in dry diethyl ether (2.0 mL) was added to the reaction mixture at 0 8C. After stirring at 0 8C for 30 min followed by warming to ambient temperature, the mixture was stirred for 16 h. Ethyl acetate (5 mL) was added to the mixture and it was poured into dichloromethane (30 mL). The solution was washed with brine (10 mL  3), dried

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Full Paper over anhydrous MgSO4, and evaporated to dryness under reduced pressure. The crude product was recrystallized from n-hexane to give pure 1 a as colorless crystals (420 mg, 62 %). Rf = 0.75 (SiO2 ; chloroform/n-hexane, 1:2); m.p. 179.5–182.5 8C; 1H NMR (CDCl3) d = 7.14 (3 H, t, J = 7.6 Hz; 4-Ar-H), 6.91 (6 H, dd, J = 0.54, 7.7 Hz; 3,5-ArH), 2.02 ppm (18 H, s, CH3); MS (ESI): m/z: 345 ([M + F]); IR (KBr): n˜ = 3049 (Ar), 2958 (CH3), 2926 (CH3), 1588 (Ar), 1448 (Ar), 1241 (Ar), 1201 (Ar), 870 (Ar), 776 (Ar), 767 (Ar), 672 cm1 (Ar); elemental calcd (%) for C36H27B: C 88.35, H 8.34; found: C 88.31, H 8.58. Synthesis of tris{2-(5-N,N-diphenylamino-m-xylyl)}borane (1 c): As the first step, 2-bromo-5-N,N-diphenylamino-m-xylene was synthesized similar to the literature method.[17] An oven-dried threenecked flask equipped with a Dimroth condenser was evacuated and filled subsequently with argon gas. Into the vessel were added diphenylamine (1.2 g, 6.8 mmol), copper(I) iodide (64 mg, 0.34 mmol), 2,2’-bipyridine (55 mg, 0.35 mmol), and potassium tertbutoxide (1.5 g, 13 mmol), followed by 2,5-dibromo-m-xylene (2.1 g, 8.0 mmol) in dry toluene (5 mL). The reaction mixture was heated at 125 8C for 24 h. After the reaction was completed, the mixture was suspended in dichloromethane (50 mL) and washed with brine (50 mL  2). The aqueous layer was extracted with dichloromethane (50 mL). The organic phase was dried over anhydrous MgSO4 and evaporated to dryness under reduced pressure. Purification by column chromatography (SiO2 ; dichloromethane/nhexane 1:3) afforded 2-bromo-5-(N,N-diphenylamino)-m-xylene as colorless solids (760 mg, 32 %). Rf = 0.65 (SiO2 ; dichloromethane/ n-hexane, 1:3); m.p. 158.7–164.6 8C; 1H NMR (CDCl3): d = 7.27–7.21 (4 H, m; 3,5-Ar-H of Ph), 7.05–7.01 (6 H, m; 2,4,6-Ar-H of Ph), 6.81 (2 H, s; 3’,5’-Ar-H of Xy), 2.31 ppm (6 H, s; CH3); MS (EI): m/z: 352 [M] + ; IR (KBr): n˜ = 3032 (Ar), 2920 (CH3), 1942 (Ar), 1582 (Ar), 1489 (Ar), 1467 (Ar), 1342 (Ar), 1280 (Ar), 1232 (Ar), 1171 (Ar), 1155 (Ar), 1075 (Ar), 1016 (Ar), 859 (Ar), 759 (Ar), 695 cm1 (Ar). An oven-dried Schlenk tube was evacuated and filled subsequently with argon gas. Into the vessel were added 2-bromo-5-N,N-diphenylamino-m-xylene (0.35 g, 1.0 mmol) and dry diethyl ether (4.0 mL) and, then, the mixture was cooled to 78 8C in an acetone/dry ice bath for 30 min. tBuLi (1.57 m in n-pentane, 1.3 mL, 2.0 mmol) was added dropwise to the reaction mixture at 78 8C. After stirring at 78 8C for 30 min, the mixture was allowed to warm to 0 8C and, then, stirred for 30 min. Boron trifluoride diethyl etherate (40 mL, 0.33 mmol) in dry diethyl ether (0.4 mL) was added to the reaction mixture at 0 8C. After stirring at 0 8C for 30 min, the reaction mixture was allowed to warm to ambient temperature followed by stirring for 16 h. The mixture was poured into dichloromethane (30 mL), washed with brine (10 mL  3), dried over anhydrous MgSO4, and evaporated to dryness under reduced pressure. The crude product was purified by column chromatography (SiO2, chloroform/n-hexane = 1/3) and recrystallized twice from chloroform/n-hexane to give pure 1 c as yellow needles (41 mg, 16 %). Rf = 0.49 (SiO2 ; chloroform/n-hexane, 1:3); m.p. 266.1–268.2 8C; 1 H NMR (CDCl3): d = 7.31–7.21 (12 H, m; 3,5-Ar-H of Ph), 7.09 (12 H, td, J = 1.3, 7.5 Hz; 2,6-Ar-H of Ph), 7.02 (6 H, tt, J = 1.2, 7.3 Hz; 4-ArH of Ph), 6.63 (6 H, s; 3’5’-Ar-H of Xy), 1.98 ppm (18 H, s; CH3); MS (ESI): m/z: 851 [M + Na] + ; IR (KBr): n˜ = 3034 (Ar), 2949 (CH3), 2910 (CH3), 1584 (Ar), 1492 (Ar), 1334 (Ar), 1296 (Ar), 1212 (Ar), 1142 (Ar), 858 (Ar), 752 (Ar), 697 cm1 (Ar); elemental analysis cald for C60H54BN3 : C 87.04, H 6.57, N 5.08; found: C 87.18, H 6.70, N 4.83. Synthesis of tris[9-{10-(9H-carbazolyl)anthryl}]borane (2 b): As the first step, 9-bromo-10-(9H-carbazolyl)anthracene was synthesized similar to the synthesis of 1 c. An oven-dried three-necked flask equipped with a Dimroth condenser was evacuated and filled subsequently with argon gas. Into the vessel were added carbazole (1.2 g, 7.1 mmol), 9,10-dibromoanthracene (2.4 g, 7.1 mmol), Chem. Eur. J. 2014, 20, 3940 – 3953

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copper powder (44 mg, 0.71 mmol), 18-crown-6 (190 mg, 0.71 mmol), potassium carbonate (3.9 g, 28 mmol), and o-dichlorobenzene (15 mL). The reaction mixture was heated at 180 8C for 20 h. After the reaction was completed, the mixture was suspended in chloroform (200 mL) and, then, insoluble solids were removed by filtration. The filtrate was washed with brine (100 mL  3), dried over anhydrous MgSO4, and evaporated to dryness under reduced pressure. Two chromatographic purifications (SiO2 ; chloroform/n-hexane, 4:1 and, then, SiO2 ; chloroform/n-hexane, 1:4) followed by recrystallization from chloroform/n-hexane afforded 9bromo-10-(9H-carbazolyl)anthracene as yellow needles (430 mg, 14 %). Rf = 0.58 (SiO2 ; chloroform/n-hexane, 1:4); 1H NMR (CDCl3): d = 8.72 (2 H, td, J = 0.9, 8.9 Hz; 4,5-Ar-H of An), 8.29 (2 H, td, J = 1.3, 7.0 Hz; 1,8-Ar-H of An), 7.67–7.61 (2 H, m; 3,6-Ar-H of An), 7.35–7.24 (8 H, m; 2,7-Ar-H of An and 1’,2’,3’,6’,7’,8’-Ar-H of Cz), 6.72 ppm (2 H, td, J = 1.0, 7.0 Hz; 4’,5’-Ar-H of Cz); MS (EI): m/z: 421 [M] + . An oven-dried Schlenk tube was evacuated and filled subsequently with argon gas. Into the vessel were added 9-bromo-10-(9H-carbazolyl)anthracene (210 mg, 0.50 mmol) and dry diethyl ether (2.0 mL) and, then, the mixture was cooled to 78 8C in an acetone/dry ice bath for 30 min. tBuLi (1.57 m in n-pentane, 0.67 mL, 1.1 mmol) was added dropwise to the reaction mixture at 78 8C. After stirring at 78 8C for 30 min, the mixture was allowed to warm to ambient temperature and, then, stirred for 30 min. Boron trifluoride diethyl etherate (20 mL, 0.17 mmol) in dry diethyl ether (0.4 mL) was added to the reaction mixture at 0 8C using an ice bath. After stirring at 0 8C for 60 min and at ambient temperature for 16 h, the mixture was poured into dichloromethane (30 mL), insoluble solids were removed by filtration and, then, the filtrate was evaporated to dryness under reduced pressure. The crude product was purified by column chromatography (SiO2 ; chloroform/nhexane, 1:2) followed by preparative HPLC (GPC, chloroform) to give pure 2 b as reddish-orange solids (ca. 3 mg, 2 %). Rf = 0.14 (SiO2 ; chloroform/n-hexane, 1:2); 1H NMR (CD2Cl2): d = 8.43 (6 H, d, J = 8.6 Hz; 1,8-Ar-H of An), 8.34–8.31 (6 H, m; 4,5-Ar-H of An), 7.38– 7.14 (30 H, m; 2,3,6,7-Ar-H of An and 1’,2’,3’,6’,7’,8’-Ar-H of Cz), 6.80–6.77 ppm (6 H, m; 4’,5’-Ar-H of Cz); MS (ESI): m/z: 1057 [M + F] . Synthesis of tris{9-(10-N,N-diphenylaminoanthryl)}borane (2 c): As the first step, 9-bromo-10-N,N-diphenylaminoanthracene was synthesized similar to the synthesis of 1 c. An oven-dried threenecked flask equipped with a Dimroth condenser was evacuated and filled subsequently with argon gas. Into the vessel were added diphenylamine (2.5 g, 15 mmol), copper(I) iodide (280 mg, 1.5 mmol), 2,2’-bipyridine (230 mg, 1.5 mmol), potassium tert-butoxide (3.3 g, 30 mmol), 9,10-dibromoanthracene (5.0 g, 15 mmol), and dry toluene (30 mL). The reaction mixture was heated at 125 8C for 33 h. After the reaction, the mixture was suspended in chloroform (500 mL), and insoluble solids were removed by filtration. The filtrate was washed with water (200 mL  3), dried over anhydrous MgSO4, and evaporated to dryness under reduced pressure. Two chromatographic purifications (SiO2 ; chloroform/nhexane, 3:2 and, then, SiO2 ; chloroform/n-hexane, 1:4) followed by recrystallization from chloroform/n-hexane afforded 9-bromo-10N,N-diphenylaminoanthracene as yellow needles (240 mg, 4 %). Rf = 0.38 (SiO2 ; chloroform/n-hexane, 1:4); m.p. 216.8–219.6 8C; 1 H NMR (CDCl3): d = 8.61 (2 H, td, J = 1.0, 8.9 Hz; 4,5-Ar-H of An), 8.10 (2 H, td, J = 0.8, 8.9 Hz; 1,8-Ar-H of An), 7.60–7.54 (2 H, m; 2,7Ar-H of An or 3,6-Ar-H of An), 7.45–7.39 (2 H, m; 2,7-Ar-H of An or 3,6-Ar-H of An), 7.19–7.12 (4 H, m; 2’,6’-Ar-H of Ph or 3’,5’-Ar-H of Ph), 7.07–7.02 (4 H, m; 2’,6’-Ar-H of Ph or 3’,5’-Ar-H of Ph), 6.88 ppm (2 H, tt, J = 1.3, 7.2 Hz; 4’-Ar-H of Ph); MS (EI): m/z: 424

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Full Paper [M] + ; IR (KBr): n˜ = 3036 (Ar), 1587 (Ar), 1487 (Ar), 1351 (Ar), 1295 (Ar), 1278 (Ar), 1027 (Ar), 916 (Ar), 751 (Ar), 693 cm1 (Ar). An oven-dried Schlenk tube was evacuated and filled subsequently with argon gas. Into the vessel were added 9-bromo-10-N,N-diphenylaminoanthracene (200 mg, 0.47 mmol) and dry diethyl ether (2.0 mL) and, then, the mixture was cooled to 78 8C in an acetone/dry ice bath for 30 min. nBuLi (1.62 m in n-hexane, 0.35 mL, 0.57 mmol) was added dropwise to the reaction mixture at 78 8C. After stirring at 78 8C for 45 min, the mixture was allowed to warm to 0 8C and, then, stirred for 20 min. Boron trifluoride diethyl etherate (20 mL, 0.17 mmol) in dry diethyl ether (0.4 mL) was added to the reaction mixture at 0 8C. After stirring at 0 8C for 30 min, the reaction mixture was allowed to warm to ambient temperature and stirred for further 12 h. The mixture was poured into chloroform (30 mL), insoluble solids were removed by filtration and, then, the filtrate was evaporated to dryness under reduced pressure. The crude product was purified by column chromatography (SiO2 ; chloroform/n-hexane, 2:3) followed by recrystallization from chloroform/n-hexane to give pure 2 c as deep-red needles (46 mg, 26 %). Rf = 0.34 (SiO2 ; chloroform/n-hexane, 2:3); m.p. > 300 8C (decomp.); 1H NMR (CDCl3): d = 8.18 (6 H, ddd, J = 0.76, 1.0, 4.6 Hz; 4,5-Ar-H of An), 8.15 (6 H, ddd, J = 0.78, 1.2, 4.7 Hz; 1,8-Ar-H of An), 7.31–7.08 (30 H, m; 2’,3’,4’,5’,6’-Ar-H of Ph), 7.00–6.88 ppm (12 H, m; 2,3,6,7-Ar-H of An); IR (KBr): n˜ = 3068 (Ar), 3034 (Ar), 1589 (Ar), 1493 (Ar), 1482 (Ar), 1404 (Ar), 1268 (Ar), 772 (Ar), 748 (Ar), 692 cm1 (Ar); MS (ESI): m/z: 1044 [M] + ; elemental analysis calcd (%) for C78H54BN3·CHCl3·1.5H2O: C 79.70, H 4.91, Cl 8.93, N 3.53; found: C 79.57, H 4.88, Cl 8.88, N 3.46.

Electrochemical measurements Cyclic and differential pulse voltammograms were recorded on an electrochemical analyzer (BAS, ALS-701 A) with a three-electrode system by using glassy carbon working, Pt auxiliary, and SCE (saturated calomel electrode) reference electrodes. The voltammograms in the positive and negative potential regions were measured separately using CH2Cl2 and THF as solvents, respectively. The concentrations of the derivatives were set ca. 1  103 m, and 0.1 m of tetra-n-butylammonium hexafluorophosphate (TBAPF6) was used as a supporting electrolyte. Sample solutions were deaerated by using an Ar gas stream over 20 min prior to the experiments. The potential was swept at 100 mV s1 in cyclic voltammetry. Differential pulse voltammetry was conducted with 50 mV height pulses (0.05 s duration) being stepped by 5.0 mV intervals (2.0 s interval between the two pulses).

a fluorescence standard, respectively, and, S, A, and n are the area of a fluorescence spectrum, the absorbance at an excitation wavelength, and the refractive index of a solvent used, respectively. Fluorescence decay measurements were conducted by using a time-correlated single-photon counting system.[30] Optically parametric amplified 400 nm laser pulses (repetition rate: 100 kHz, fwhm: 200 fs autocorrelation trace, Coherent, model 9400) of the output pulses from a mode-locked Ti:sapphire laser (Coherent, Mira model 900-F) or 405 nm laser pulses (repetition rate: 100 MHz, fwhm: 70 ps) from a picoseconds light pulser (Hamamatsu, PLP10–040) were used as an excitation light source. By using a Soleil–Babinet compensator (Melles Griot), the polarized direction of the excitation laser beam was set at a magic angle (54.78) or vertical direction for fluorescence decay measurements. Fluorescence from a sample was detected by a microchannel-plate photomultiplier (Hamamatsu, R3809U-50) equipped with a monochromator (Jobin Ybon, H-20) and analyzed by a single-photon counting module (Edinburgh Instruments, SPC-300). The excitation laser pulse profile was measured at the excitation wavelength by using dye-free polystyrene resins as a scattering material. Decay profiles were analyzed by an iterative nonlinear least-squares deconvolution method. The absorbance of a sample solution was set < 0.05 at the excitation wavelength, and sample solutions were deaerated by using an argon gas stream over 30 min.

Theoretical calculations Theoretical calculations for the derivatives were conducted on the Gaussian 09W programs.[31] The ground-state geometries of the derivatives were optimized by using the B3LYP density functional theory (DFT)[32] and 6–31G* basis set. Time-dependent DFT (TDDFT) calculations were then performed to estimate the energies and oscillator strengths of the five lowest-energy electronic transitions of the derivatives. All the calculations were carried out as THF solutions by the Polarizable Continuum Model (PCM). The contours of the electron density were plotted by using GaussView 5.0.[33]

Acknowledgements This work was partly supported by Grant-in-Aid from MEXT for Young Scientists (B) under Grant Number 23750141 to ES. Keywords: charge transfer · fluorescence · photophysics · solvent effects · triarylboranes

Spectroscopic measurements Absorption and corrected fluorescence spectra of the derivatives were measured by using a Hitachi UV-3300 spectrophotometer and a Hamamatsu multichannel photodetector (PMA-11, excitation wavelength = 355 or 532 nm), respectively. The fluorescence quantum yields (Ff) of the derivatives were determined relative to that of 9,10-diphenylanthracene (Ff = 0.91 in cyclohexane),[26] perylene (Ff = 0.92 in ethanol),[27] or rhodamine 6G (Ff = 0.94 in ethanol).[27c, 28] The photon number of a fluorescence spectrum was corrected in a wavenumber scale by using an equation, I(n˜ ) = I(l)  l2,[29] and Ff calculated based on Equation (4):

f;sample

  ssample =Asample nsample 2 ¼ f;std nstd sstd =Astd

ð4Þ

where the subscripts “sample” and “std” represent a sample and Chem. Eur. J. 2014, 20, 3940 – 3953

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[1] a) N. Tian, A. Thiessen, R. Schiewek, O. J. Schmitz, D. Hertel, K. Meerholz, E. Holder, J. Org. Chem. 2009, 74, 2718 – 2725; b) N. Tian, D. Lenkeit, S. Pelz, D. Kourkoulos, D. Hertel, K. Meerholz, E. Holder, Dalton Trans. 2011, 40, 11629 – 11635; c) D. Kourkoulos, C. Karakus, D. Hertel, R. Alle, S. Schmeding, J. Hummel, N. Risch, E. Holder, K. Meerholz, Dalton Trans. 2013, 42, 13612 – 13621. [2] a) L. H. Fischer, M. I. J. Stich, O. S. Wolfbeis, N. Tian, E. Holder, M. Schferling, Chem. Eur. J. 2009, 15, 10857 – 10863; b) N. Tian, D. Lenkeit, S. Pelz, L. H. Fischer, D. Escudero, R. Schiewek, D. Klink, O. J. Schmitz, L. Gonzlez, M. Schferling, E. Holder, Eur. J. Inorg. Chem. 2010, 4875 – 4885; c) L. H. Fischer, C. Karakus, R. J. Meier, N. Risch, O. S. Wolfbeis, E. Holder, M. Schferling, Chem. Eur. J. 2012, 18, 15706 – 15713; d) C. Karakus, L. H. Fischer, S. Schmeding, J. Hummel, N. Risch, M. Schaferling, E. Holder, Dalton Trans. 2012, 41, 9623 – 9632. [3] N. Kitamura, E. Sakuda, Y. Ando, Chem. Lett. 2009, 38, 938 – 943. [4] H. C. Brown, V. H. Dodson, J. Am. Chem. Soc. 1957, 79, 2302 – 2306. [5] S. Yamaguchi, S. Akiyama, K. Tamao, J. Am. Chem. Soc. 2000, 122, 6335 – 6336. [6] N. Kitamura, E. Sakuda, J. Phys. Chem. A 2005, 109, 7429 – 7434.  2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper [7] N. Kitamura, E. Sakuda, T. Yoshizawa, T. Iimori, N. Ohta, J. Phys. Chem. A 2005, 109, 7435 – 7441. [8] a) K. Parab, K. Venkatasubbaiah, F. Jkle, J. Am. Chem. Soc. 2006, 128, 12879 – 12885; b) H. Li, F. Jkle, Macromol. Rapid Commun. 2010, 31, 915 – 920; c) P. Chen, F. Jkle, J. Am. Chem. Soc. 2011, 133, 20142 – 20145; d) H. Li, F. Jkle, Polym. Chem. 2011, 2, 897 – 905. [9] a) E. Sakuda, A. Funahashi, N. Kitamura, Inorg. Chem. 2006, 45, 10670 – 10677; b) Y. Sun, N. Ross, S.-B. Zhao, K. Huszarik, W.-L. Jia, R.-Y. Wang, D. Macartney, S. Wang, J. Am. Chem. Soc. 2007, 129, 7510 – 7511; c) S.-B. Zhao, T. McCormick, S. Wang, Inorg. Chem. 2007, 46, 10965 – 10967; d) Y. You, S. Y. Park, Adv. Mater. 2008, 20, 3820 – 3826; e) G. Zhou, C.-L. Ho, W.-Y. Wong, Q. Wang, D. Ma, L. Wang, Z. Lin, T. B. Marder, A. Beeby, Adv. Funct. Mater. 2008, 18, 499 – 511; f) Y.-L. Rao, S. Wang, Inorg. Chem. 2009, 48, 7698 – 7713; g) C. R. Wade, F. P. Gabbai¨, Inorg. Chem. 2010, 49, 714 – 720; h) Z. M. Hudson, S.-B. Zhao, R.-Y. Wang, S. Wang, Chem. Eur. J. 2009, 15, 6131 – 6137; i) A. Ito, T. Hiokawa, E. Sakuda, N. Kitamura, Chem. Lett. 2011, 40, 34 – 36; j) E. Sakuda, Y. Ando, A. Ito, N. Kitamura, Inorg. Chem. 2011, 50, 1603 – 1613; k) Y. Sun, Z. M. Hudson, Y. Rao, S. Wang, Inorg. Chem. 2011, 50, 3373 – 3378; l) Z. M. Hudson, C. Sun, K. J. Harris, B. E. G. Lucier, R. W. Schurko, S. Wang, Inorg. Chem. 2011, 50, 3447 – 3457; m) R. S. Vadavi, H. Kim, K. M. Lee, T. Kim, J. Lee, Y. S. Lee, M. H. Lee, Organometallics 2012, 31, 31 – 34; n) C. Baik, S. Wang, Chem. Commun. 2011, 47, 9432 – 9434; o) Z. M. Hudson, M. G. Helander, Z.-H. Lu, S. Wang, Chem. Commun. 2011, 47, 755 – 757; p) A. Ito, Y. Kang, S. Saito, E. Sakuda, N. Kitamura, Inorg. Chem. 2012, 51, 7722 – 7732. [10] a) N. Matsumi, K. Naka, Y. Chujo, J. Am. Chem. Soc. 1998, 120, 10776 – 10777; b) W.-L. Jia, D. Song, S. Wang, J. Org. Chem. 2003, 68, 701 – 705; c) Y. Qin, I. Kiburu, S. Shah, F. Jkle, Macromolecules 2006, 39, 9041 – 9048; d) Y. Nagata, Y. Chujo, Macromolecules 2008, 41, 2809 – 2813; e) Y. Nagata, Y. Chujo, Macromolecules 2008, 41, 3488 – 3492; f) S.-T. Lam, N. Zhu, V. W.-W. Yam, Inorg. Chem. 2009, 48, 9664 – 9670; g) A. Lorbach, M. Bolte, H. Li, H.-W. Lerner, M. C. Holthausen, F. Jkle, M. Wagner, Angew. Chem. 2009, 121, 4654 – 4658; Angew. Chem. Int. Ed. 2009, 48, 4584 – 4588; h) D. Reitzenstein, C. Lambert, Macromolecules 2009, 42, 773 – 782; i) A. G. Crawford, A. D. Dwyer, Z. Liu, A. Steffen, A. Beeby, L.-O. Pa8lsson, D. J. Tozer, T. B. Marder, J. Am. Chem. Soc. 2011, 133, 13349 – 13362. [11] a) Z. Yuan, N. J. Taylor, T. B. Marder, I. D. Williams, S. K. Kurtz, L.-T. Cheng, J. Chem. Soc. Chem. Commun. 1990, 1489 – 1492; b) Z. Yuan, N. J. Taylor, Y. Sun, T. B. Marder, I. D. Williams, C. Lap-Tak, J. Organomet. Chem. 1993, 449, 27 – 37; c) C. D. Entwistle, T. B. Marder, Chem. Mater. 2004, 16, 4574 – 4585; d) L. Zhao, G. Yang, Z. Su, L. Yan, J. Mol. Struct. 2008, 855, 69 – 76; e) Y. Liu, W. Xuan, H. Zhang, Y. Cui, Inorg. Chem. 2009, 48, 10018 – 10023; f) W. Z. Yuan, S. Chen, J. W. Y. Lam, C. Deng, P. Lu, H. H. Y. Sung, I. D. Williams, H. S. Kwok, Y. Zhang, B. Z. Tang, Chem. Commun. 2011, 47, 11216 – 11218. [12] a) S. Yamaguchi, S. Akiyama, K. Tamao, J. Am. Chem. Soc. 2001, 123, 11372 – 11375; b) S. Yamaguchi, S. Akiyama, K. Tamao, J. Organomet. Chem. 2002, 652, 3 – 9; c) Y. Kubo, M. Yamamoto, M. Ikeda, M. Takeuchi, S. Shinkai, S. Yamaguchi, K. Tamao, Angew. Chem. 2003, 115, 2082 – 2086; Angew. Chem. Int. Ed. 2003, 42, 2036 – 2040; d) M. Melaimi, F. P. Gabbaı¨, J. Am. Chem. Soc. 2005, 127, 9680 – 9681; e) Z. Zhou, S. Xiao, J. Xu, Z. Liu, M. Shi, F. Li, T. Yi, C. Huang, Org. Lett. 2006, 8, 3911 – 3914; f) Z. Zhou, H. Yang, M. Shi, S. Xiao, F. Li, T. Yi, C. Huang, ChemPhysChem 2007, 8, 1289 – 1292; g) T. W. Hudnall, Y.-M. Kim, M. W. P. Bebbington, D. Bourissou, F. o. P. Gabbai¨, J. Am. Chem. Soc. 2008, 130, 10890 – 10891; h) Y. Kim, F. P. Gabbai¨, J. Am. Chem. Soc. 2009, 131, 3363 – 3369; i) J. Feng, K. Tian, D. Hu, S. Wang, S. Li, Y. Zeng, Y. Li, G. Yang, Angew. Chem. 2011, 123, 8222 – 8226; Angew. Chem. Int. Ed. 2011, 50, 8072 – 8076; j) H. Li, R. A. Lalancette, F. Jkle, Chem. Commun. 2011, 47, 9378 – 9380; k) H. C. Schmidt, L. G. Reuter, J. Hamacek, O. S. Wenger, J. Org. Chem. 2011, 76, 9081 – 9085; l) Y.-H. Zhao, H. Pan, G.-L. Fu, J.-M. Lin, C.-H. Zhao, Tetrahedron Lett. 2011, 52, 3832 – 3835. [13] a) Y.-L. Rao, H. Amarne, S.-B. Zhao, T. M. McCormick, S. Martic´, Y. Sun, R.Y. Wang, S. Wang, J. Am. Chem. Soc. 2008, 130, 12898 – 12900; b) C.-T. Poon, W. H. Lam, V. W.-W. Yam, J. Am. Chem. Soc. 2011, 133, 19622 – 19625. [14] a) Z. M. Hudson, S. Wang, Acc. Chem. Res. 2009, 42, 1584 – 1596; b) Y. Sun, S. Wang, Inorg. Chem. 2009, 48, 3755 – 3767; c) M. Steeger, C. Lambert, Chem. Eur. J. 2012, 18, 11937 – 11948; d) A. K. C. Mengel, B. He, O. S. Wenger, J. Org. Chem. 2012, 77, 6545 – 6552. Chem. Eur. J. 2014, 20, 3940 – 3953

www.chemeurj.org

[15] S. Yamaguchi, T. Shirasaka, K. Tamao, Org. Lett. 2000, 2, 4129 – 4132. [16] E. Sakuda, Y. Ando, A. Ito, N. Kitamura, J. Phys. Chem. A 2010, 114, 9144 – 9150. [17] R. Stahl, C. Lambert, C. Kaiser, R. Wortmann, R. Jakober, Chem. Eur. J. 2006, 12, 2358 – 2370. [18] a) M. E. Casida, C. Jamorski, K. C. Casida, D. R. Salahub, J. Chem. Phys. 1998, 108, 4439 – 4449; b) M. E. Casida, D. R. Salahub, J. Chem. Phys. 2000, 113, 8918 – 8935; c) N. N. Matsuzawa, A. Ishitani, D. A. Dixon, T. Uda, J. Phys. Chem. A 2001, 105, 4953 – 4962; d) H. Appel, E. K. U. Gross, K. Burke, Phys. Rev. Lett. 2003, 90, 043005; e) Y. Tawada, T. Tsuneda, S. Yanagisawa, T. Yanai, K. Hirao, J. Chem. Phys. 2004, 120, 8425 – 8433. [19] a) L. Bilot, A. Kawski, Z. Naturforsch. 1962, 17a, 621 – 627; b) A. Kawski, Z. Naturforsch. 2002, 57a, 255 – 262; c) A. Kawski, P. Bojarski, B. Kuklin´ski, Chem. Phys. Lett. 2008, 463, 410 – 412; d) U. S. Raikar, C. G. Renuka, Y. F. Nadaf, B. G. Mulimani, A. M. Karguppikar, M. K. Soudagar, Spectrochim. Acta Part A 2006, 65, 673 – 677; e) J. R. Mannekutla, B. G. Mulimani, S. R. Inamdar, Spectrochim. Acta Part A 2008, 69, 419 – 426. [20] a) J. V. Caspar, E. M. Kober, B. P. Sullivan, T. J. Meyer, J. Am. Chem. Soc. 1982, 104, 630 – 632; b) J. V. Caspar, B. P. Sullivan, E. M. Kober, T. J. Meyer, Chem. Phys. Lett. 1982, 91, 91 – 95; c) J. V. Caspar, T. J. Meyer, J. Phys. Chem. 1983, 87, 952 – 957; d) W. J. Vining, J. V. Caspar, T. J. Meyer, J. Phys. Chem. 1985, 89, 1095 – 1099; e) E. M. Kober, J. V. Caspar, R. S. Lumpkin, T. J. Meyer, J. Phys. Chem. 1986, 90, 3722 – 3734; f) S. R. Johnson, T. D. Westmoreland, J. V. Caspar, K. R. Barqawi, T. J. Meyer, Inorg. Chem. 1988, 27, 3195 – 3200. [21] a) R. Englman, J. Jortner, Mol. Phys. 1970, 18, 145 – 164; b) K. F. Freed, J. Jortner, J. Chem. Phys. 1970, 52, 6272 – 6291; c) E. W. Schlag, S. Schneider, S. F. Fischer, Annu. Rev. Phys. Chem. 1971, 22, 465 – 526; d) K. F. Freed, Acc. Chem. Res. 1978, 11, 74 – 80; e) J. V. Caspar, T. J. Meyer, Inorg. Chem. 1983, 22, 2444 – 2453; f) J. V. Caspar, T. J. Meyer, J. Am. Chem. Soc. 1983, 105, 5583 – 5590; g) G. H. Allen, R. P. White, D. P. Rillema, T. J. Meyer, J. Am. Chem. Soc. 1984, 106, 2613 – 2620; h) R. S. Lumpkin, T. J. Meyer, J. Phys. Chem. 1986, 90, 5307 – 5312; i) K. R. Bargawi, A. Llobet, T. J. Meyer, J. Am. Chem. Soc. 1988, 110, 7751 – 7759; j) P. Y. Chen, R. Duesing, D. K. Graff, T. J. Meyer, J. Phys. Chem. 1991, 95, 5850 – 5858; k) K. R. Barqawi, Z. Murtaza, T. J. Meyer, J. Phys. Chem. 1991, 95, 47 – 50; l) L. A. Worl, R. Duesing, P. Y. Chen, L. Dellaciana, T. J. Meyer, J. Chem. Soc. Dalton Trans. 1991, 849 – 858; m) Y.-P. Sun, T. L. Bowen, C. E. Bunker, J. Phys. Chem. 1994, 98, 12486 – 12494; n) M. Bixon, J. Jortner, J. Cortes, H. Heitele, M. E. Michel-Beyerle, J. Phys. Chem. 1994, 98, 7289 – 7299; o) P. Chen, T. J. Meyer, Chem. Rev. 1998, 98, 1439 – 1477; p) A. Morimoito, T. Yatsuhashi, T. Shimada, L. Biczk, D. A. Tryk, H. Inoue, J. Phys. Chem. A 2001, 105, 10488 – 10496; q) D. W. Thompson, C. N. Fleming, B. D. Myron, T. J. Meyer, J. Phys. Chem. B 2007, 111, 6930 – 6941; r) A. Ito, T. J. Meyer, Phys. Chem. Chem. Phys. 2012, 14, 13731 – 13745. [22] 1H NMR (CD2Cl2): d = 8.17 (d, 6 H, J = 7.8 Hz; 4,5-Ar-H), 7.55 (d, 6 H, J = 8.2 Hz; 1,8-Ar-H), 7.45 (dt, 6 H, J = 1.3, 7.6 Hz; 2,7-Ar-H), 7.30 (dt, 6 H, J = 1.0, 7.4 Hz; 3,6-Ar-H), 7.30 (s, 6 H; 3’,5’-Ar-H), 2.35 ppm (s, 18 H; CH3); IR (KBr): n˜ = 3051 (CH3), 1591 (Ar), 1451 (Ar), 1346 (Ar), 1230 (Ar), 749 (Ar), 722 cm1 (Ar); elemental analysis calcd for C60H48BN3·CH2Cl2 : C 80.79, H 5.56, N 4.63, Cl 7.82; found: C 80.69, H 5.55, N 4.63, Cl 7.55. [23] M.p. 300 8C (decomp.); 1H NMR (CDCl3): d = 8.54 (3 H, s; 10-Ar-H), 8.05 (6 H, dd, J = 0.84, 8.9 Hz; 1,8-Ar-H), 7.97 (6 H, d, J = 8.4 Hz; 4,5-Ar-H), 7.31–7.24 (6 H, m; 2,7-Ar-H), 6.90 (6 H, dt, J = 1.4, 8.3 Hz; 3,6-Ar-H); IR (KBr) n˜ = 3044 (Ar), 1945 (Ar), 1508 (Ar), 1248 (Ar), 1159 (Ar), 1078 (Ar), 1068 (Ar), 880 (Ar), 733 cm1 (Ar); MS (ESI): m/z: 562 [M + F] ; elemental analysis calcd for C42H27B: C 92.99, H 5.02; found: C 92.83, H 5.23. [24] D. D. Perrin, W. L. F. Armarego, D. R. Perrin, Purification of Laboratory Chemicals, 2nd ed., Pargamon Press, New York, 1980. [25] B. G. Ramsey, L. M. Isabelle, J. Org. Chem. 1981, 46, 179 – 182. [26] S. R. Meech, D. Phillips, J. Photochem. 1983, 23, 193 – 217. [27] a) G. A. Crosby, J. N. Demas, J. Phys. Chem. 1971, 75, 991 – 1024; b) A. A. Rachford, S. b. Goeb, R. Ziessel, F. N. Castellano, Inorg. Chem. 2008, 47, 4348 – 4355; c) Handbook of Photochemistry, 3rd ed., Taylor & Francis CRC Press, Oxon, U. K., 2006. [28] M. Fischer, J. Georges, Chem. Phys. Lett. 1996, 260, 115 – 118. [29] a) C. A. Parker, W. T. Rees, Analyst 1960, 85, 587 – 600; b) B. Valeur, Molecular Fluorescence: Principles and Applications, 3rd ed., Wiley-VCH, Weinheim: New York, 2006. [30] H.-B. Kim, S. Habuchi, N. Kitamura, Anal. Chem. 1999, 71, 842 – 848.

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Full Paper [31] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. J. A. Montgomery, J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox, Gaussian 09 (Revision A.1), Gaussian, Inc., Wallingford CT, 2009.

Chem. Eur. J. 2014, 20, 3940 – 3953

www.chemeurj.org

[32] a) P. Hohenberg, W. Kohn, Phys. Rev. 1964, 136, B864 – B871; b) W. Kohn, L. J. Sham, Phys. Rev. 1965, 140, A1133 – A1138; c) R. G. Parr, W. Yang, Density-Functional Theory of Atoms and Molecules, Oxford University Press, New York 1989. [33] R. Dennington, T. Keith, J. Millam, GaussView, Version 5, Semichem, Shawnee Mission KS, 2009. [34] Organic Solvents, Techniques of Chemistry, Vol. II, Wiley Interscience, New York, 1970.

Received: October 19, 2013 Published online on March 18, 2014

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