Through-space charge transfer and emission color tuning of di-o-carborane substituted benzene

Article abstract of DOI:10.1039/c3dt52465e

1,4-Di-(1-Ar-o-carboran-2-yl)benzene (Ar = 3,5-bis(trifluoromethyl)phenyl (1), phenyl (2), 4-n-butylphenyl (3), 4-N,N-dimethylaniline (4)) compounds that are electronically modulated at the C1-position of o-carborane with the electron-withdrawing or -donating aryl groups were prepared and characterized. The X-ray crystal structures of 1, 3, and 4 reveal that the two aryl groups on the C1-carborane carbon atoms are oppositely positioned, featuring overall C₂-symmetry, and the C1-C2 bond length of carborane increases with the increasing order of electron-donating effect of an aryl group. UV-vis absorption spectra exhibit small low-energy absorption bands at around 275-300 nm for 1-3 while 4 shows a broad absorption tail at 350-400 nm. Although 1-4 show virtually no emission in solution, an intense aggregation-induced emission over the region ranging from 400-700 nm is observed in the solid state. Importantly, the emission wavelengths of 1-4 exhibit an apparent red-shift upon changing the aryl substituent from the CF₃ to the NMe₂ group (from 1 to 4). TD-DFT calculations suggest that the low-energy electronic transition is attributed to the intramolecular through-space charge transfer between the appended aryl group (HOMO) and the central phenylene ring (LUMO), and the greater change in the HOMO level by the substituent than that in the LUMO is responsible for the emission color tuning.

Full text of DOI:10.1039/c3dt52465e

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Through-space charge transfer and emission color
tuning of di-o-carborane substituted benzene†
Cite this: Dalton Trans., 2014, 43,
4978
Hye Jin Bae,a Hyungjun Kim,a Kang Mun Lee,a Taewon Kim,b Yoon Sup Lee,a
Youngkyu Do*a and Min Hyung Lee*b
1,4-Di-(1-Ar-o-carboran-2-yl)benzene (Ar = 3,5-bis(trifluoromethyl)phenyl (1), phenyl (2), 4-n-butylphenyl
(3), 4-N,N-dimethylaniline (4)) compounds that are electronically modulated at the C1-position of
o-carborane with the electron-withdrawing or -donating aryl groups were prepared and characterized.
The X-ray crystal structures of 1, 3, and 4 reveal that the two aryl groups on the C1-carborane carbon
atoms are oppositely positioned, featuring overall C2-symmetry, and the C1–C2 bond length of carborane
increases with the increasing order of electron-donating effect of an aryl group. UV-vis absorption
spectra exhibit small low-energy absorption bands at around 275–300 nm for 1–3 while 4 shows a broad
absorption tail at 350–400 nm. Although 1–4 show virtually no emission in solution, an intense aggrega-
tion-induced emission over the region ranging from 400–700 nm is observed in the solid state. Impor-
tantly, the emission wavelengths of 1–4 exhibit an apparent red-shift upon changing the aryl substituent
from the CF3 to the NMe2 group (from 1 to 4). TD-DFT calculations suggest that the low-energy elec-
tronic transition is attributed to the intramolecular “through-space” charge transfer between the
appended aryl group (HOMO) and the central phenylene ring (LUMO), and the greater change in the
HOMO level by the substituent than that in the LUMO is responsible for the emission color tuning.
Received 7th September 2013,
Accepted 9th October 2013
DOI: 10.1039/c3dt52465e
www.rsc.org/dalton
tuned by the substituent on an aryl group.9 The donor–accep-
tor dyads consisting of carbazole and o-carborane moieties
Introduction
ortho-Carborane (1,2-dicarba-closo-dodecarborane) has recently have also been reported by Kang and co-workers (II).7 It was
received attention in the field of luminescent materials for revealed that efficient photoinduced CT from a carbazole
the potential optoelectronic applications of o-carborane donor to a carborane acceptor forms a discrete charge-separ-
derivatives.1–3 It has been shown that the emission properties ated excited state. Fox and co-workers have reported CT tran-
of luminophores such as emission color and quantum sition in the diazaborolyl-o-carborane donor–acceptor systems
efficiency are largely affected by the incorporation of (III) and shown that the CT transition is affected by the substi-
o-carborane,1–14 probably owing to the unique properties of tuent on the carborane and molecular geometry.5 Hosmane
o-carborane such as highly polarizable σ-aromatic character et al. have reported the luminescent properties of organic
and electron-withdrawing property through C-substitution.15 π-systems decorated by o-carborane moieties (IV).10,11
Recent reports on the photophysics of carborane-containing
luminophores suggested that o-carborane is involved in the
charge transfer (CT) transition and can alter the excited state
properties of luminophores.5,7,9 For example, Chujo and co-
workers have reported that CT-based aggregation-induced
emission (AIE) can be activated in the various 1,2-diaryl-o-
carborane compounds (I) and their emission color can be fine-
aDepartment of Chemistry, KAIST, Daejeon, 305-701, Republic of Korea.
E-mail: ykdo@kaist.ac.kr; Fax: +82 42 350 2810; Tel: +82 42 350 2869
bDepartment of Chemistry and EHSRC, University of Ulsan, Ulsan 680-749, Republic
of Korea. E-mail: lmh74@ulsan.ac.kr; Fax: +82 52 259 2348; Tel: +82 52 259 2335
†Electronic supplementary information (ESI) available: Theoretical details.
The foregoing reports and our recent results1,3,4,13 on the
CCDC 943435 (for 1), 943436 (for 3), and 943437 (for 4). For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/c3dt52465e
carborane-containing luminophores suggest that o-carborane
4978 | Dalton Trans., 2014, 43, 4978–4985
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can directly participate in the lowest unoccupied molecular
The substituted aryl group with an electron-withdrawing
orbitals (LUMOs) of organic π-systems by the conjugation (CF3) or -donating (n-Bu, NMe2) moiety was introduced to
effect and thereby affecting the CT excited state. One of the modulate the electronic effect with respect to the phenyl sub-
consequences is weak or the non-emissive nature of the car- stituted compound. The final di-carborane compounds 1–4
borane-containing luminophores in solution although Núñez were prepared from the cage forming reaction of decaborane
and co-workers have demonstrated that non-conjugated car- (B10H14) with the bis-acetylene precursors (1a–4a) in the pres-
borane luminophores are appreciably luminescent.8,14,16 The ence of Et2S19,20 following the modified literature procedures
non-emissive nature was attributed to the variable nature of for 2.19 Compounds 1, 3, and 4 have been characterized by
C–C bond of o-carborane,17 which dissipates the excited state NMR spectroscopy, elemental analysis, and the X-ray diffrac-
energy via a nonradiative decay process in solution. In con- tion method. The 11B NMR signals detected in the regions of δ
trast, the solid or film state becomes emissive due to the −1 to −12 ppm confirm the presence of o-carboranyl boron
restricted rotation of the carborane moiety, resulting in the atoms. Single crystals of 1, 3, and 4 suitable for X-ray diffrac-
AIE phenomenon.18 As has been shown by Chujo and co- tion studies were obtained from slow evaporation of an
workers (I), such AIE can be useful for the emission color acetone (or THF)/MeOH solution at room temperature.† As
tuning.9
shown in Fig. 1, the carborane cages are held at the para-posi-
In a continuous effort to investigate the photophysical pro- tions of the central phenylene ring. The two aryl groups on the
perties of carborane-containing luminophores and the emis- C1-carborane carbon atoms are oppositely positioned, featur-
sion color tuning, we newly designed di-o-carborane ing C2-symmetry probably due to the steric reason. The aryl
substituted benzene compounds (1–4), in which aryl-o-carbor- and phenylene rings on the C1 and C2 atoms, respectively, are
ane cages are introduced at the 1 and 4 positions of the phenyl- oriented roughly perpendicular to the plane defined by CAr–
ene ring. By the electronic variation of the substituent on the C1–C2–CPh (avg angles: 58.2°/74.0° for 1, 87.6°/85.4° for 3,
appended aryl group at the C1-position of o-carborane from 76.7°/73.4° for 4), as has been similarly observed in other di-
electron-withdrawing to electron-donating properties, we arylcarborane compounds,21 indicating the existence of
intended to achieve color tuning of AIE. We observed the π-interaction between the aryl π-system and the anti-bonding
occurrence of “through-space” CT between the appended aryl C–C orbital (σ*(C–C)) of cage carbon atoms.17 Indeed, the C1–
group and the central phenylene ring and found that the emis- C2 bond length increases with the increasing order of the elec-
sion color of the CT transition can also be tuned by changing tron-donating effect of an aryl group (1.711(6) and 1.718(5) Å
the aryl substituent. The detailed synthesis, characterization, for 1, 1.729(3) Å for 3, 1.779(3) and 1.758(3) Å for 4), support-
and luminescent properties of 1–4 are described with theore- ing the appreciable π-interaction.9,17
tical calculations.
Optical properties
To examine the optical properties, UV-vis absorption and
photoluminescence (PL) experiments were carried out with 1–4
in both solution and solid state. All the compounds feature
major absorption bands in the region of 200–250 nm with the
vibronic structure assignable to π–π* transition in the central
phenylene ring and the appended aryl group (Fig. 2 and
Table 2). In particular, the absorption bands of 1–3 accompany
small low-energy absorption bands at around 275 nm which
Results and discussion
Synthesis and characterization
The starting bis-acetylene compounds 1a–4a were readily
obtained from Sonogashira coupling reaction between 1,4-di-
iodobenzene and various arylacetylene derivatives (Scheme 1).
tails to 300 nm. These bands could be tentatively assigned to
intramolecular π(aryl) → π*(phenylene) charge transfer (CT)
transition. In 4, the intense low-energy absorption band cen-
tered at λabs = 286 nm, which accompanies a broad tail at
350–400 nm, is clearly observed. The structureless band shape
also suggests that the absorption is mainly originated from
π(aryl) → π*(phenylene) CT transition, in which the lone pair
electrons of nitrogen atom would have a large contribution to
the aryl donation (see TD-DFT results).
Next, the emission properties of 1–4 were investigated by PL
measurements (Fig. 3 and Table 2). Compounds 1–4 show vir-
tually no emission in solution, as usually observed in other
o-carborane substituted luminophores.3,4,7–9,11,12,22 This
phenomenon could be related to the involvement of o-carbor-
ane in the excited states, which facilitates the nonradiative
Scheme 1 Synthesis of 1,4-di-(1-Ar-o-carboran-2-yl)benzene (1–4).
decay process due to the variable nature of C–C bond of car-
Conditions and reagents: (i) CuI, PdCl2(PPh3)2, NEt3–toluene, r.t., 24 h,
58–88% (1a–4a). (ii) B10H14, Et2S, toluene, 110 °C, 3 d, 6.0–68% (1–4).
borane in solution.17 From the absorption spectra, it was
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Fig. 1 Crystal structures of (a) 1, (b) 3, and (c) 4. H-atoms are omitted for clarity. Due to the disorder of three fluorine atoms of one CF3 group in 1,
the fluorine atoms were partitioned. Color code: blue = nitrogen; green = fluorine; orange = boron atom.
Fig. 2 UV-vis absorption spectra of 1–4 in THF (ca. 2 × 10−5 M).
suggested that the lowest-energy excited state in 1–4 is mainly
charge transfer in nature from the appended aryl group to the
central phenylene ring. Because the two carborane cages are
conjugated with the phenylene ring, the CT state may have a
substantial contribution from the carboranes, leading to the
emission quenching in solution. In contrast, 1–4 exhibit an
intense emission over the region ranging from 400 to 700 nm
in a rigid matrix at 77 K and in the solid state, such as a film
and a powder, i.e., aggregation-induced emission (AIE) is
observed (Fig. 3a–c). This result can be attributed to the
restricted rotation of the carborane moiety in the solid state,
which prevents the variation in the C–C bond of carborane.5
The AIE phenomenon can also be observed from a THF–water
(1 : 99, v/v) mixture (Fig. 3d). Most interestingly, the emission
Fig. 3 PL spectra of 1–4 (a) at 77 K (5 × 10−5 M in THF), (b) in the film
state (10 wt% in PMMA), (c) in the neat solid state, and (d) in a THF–H2O
mixture (1 : 99, v/v, 5 × 10−5 M).
tuned by the change of the HOMO–LUMO energy gap (see DFT
wavelengths of 1–4 exhibit an apparent shift depending on the results). This finding further suggests that the emission origi-
substituent of the aryl group under all measurement con- nates from the intramolecular “through-space” CT transition23
between the appended aryl group and the central phenylene
ditions although the difference in the wavelength between 2
(H) and 3 (n-Bu) is relatively marginal. While compound 1 ring. Although the observed emission color tuning is similar
bearing the electron-withdrawing CF3 shows the emission at a to that observed in the mono-carborane compounds, such as
bis(4-phenylethynyl)phenyl-o-carborane (I), the aryl groups in
high energy region (478–510 nm), the PL spectra are gradually
red-shifted upon changing the substituent from CF3 to the those compounds are directly conjugated with a carborane
electron-donating NMe2 group (from 1 to 4). Since the HOMO cage. Thus the excited state was characterized to be π–π*
transition with a substantial intramolecular CT character.9 In
localized in the aryl moiety should be more affected by the
substituent in comparison with the LUMO which is mostly contrast, the present di-o-carborane system utilizes discrete
located on the phenylene ring, the emission color could be π → π* charge transfer from the appended aryl donor to the
4980 | Dalton Trans., 2014, 43, 4978–4985
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phenylene acceptor which is conjugated with carborane. The computed position of the absorption band correlates well with
observed emission features for 1–4 further indicate that the the electronic property of the substituent on the appended aryl
electronic alteration of the aryl group at the C1-position of group in such a way that the band position is bathochromically
o-carborane can lead to facile tuning of the emission color.
shifted with the electron-donating substituent (1 → 4)
although the experimental shift in the absorption spectra was
not apparently distinguished among 1–3 in the region of
ca. 275 nm, presumably due to overlapping with other higher
energy bands. In contrast, the computed absorption wave-
length of 395 nm for 4 falls in the lower energy absorption
region (<400 nm). Moreover, the TD-DFT calculation indicates
that the shift in the absorption wavelength is mainly attributed
to the change in the HOMO level depending on the substitu-
ent. As shown in Fig. 4, while the LUMO levels of 1–4 are very
slightly changed, the HOMO levels gradually increase with the
increasing electron-donating effect of the substituent. This
finding is also consistent with the change in the emission
wavelength. As shown in Fig. 3, the emission wavelengths of
1–4 exhibited a gradual red shift with the electron-donating
substituent on going from 1 to 4. Because of the reduction of a
band gap due to the greater elevation of the HOMO level than
that of the LUMO, the compounds with the more electron-
donating substituent result in the more red-shifted emission.
These results thus suggest that the introduction of a substitu-
ent to the appended aryl ring of o-carborane can also allow the
color tuning of AIE by the change of the HOMO–LUMO energy
gap.
Theoretical calculation
To elucidate the nature of electronic transition and emission
color tuning properties, TD-DFT calculations on the ground
state geometry (S0) of 1–4 were performed at the B3LYP/
6-31G(d) level of theory (Fig. 4 and Table 3). It can be seen that
the lowest energy absorption in 1–4 is mainly characterized by
HOMO–LUMO transition. The LUMO in 1–4 is delocalized over
the central phenylene ring and carboranyl carbon atoms. The
contribution from the carborane cage to LUMO is found to be
substantial (23–28%). Interestingly, while the HOMO in 2–4
bears a major contribution from the appended aryl group, the
HOMO and HOMO−1 in 1 are localized in the central phenyl-
ene ring. This result could be attributed to the strong electron-
withdrawing effect of the two CF3 groups of the appended
aryl group in 1, leading to the greater stabilization of the π
level of the aryl group than that of the central phenylene
group. Consequently, the HOMO–LUMO transition in 2–4 is
mainly assignable to the π(aryl) → π*(phenylene) CT transition
while 1 has a major contribution from the π–π* transition cen-
tered on the phenylene group. Nevertheless, owing to the large
contribution of the carborane to LUMO in 1, the π–π* tran-
sition may also have a substantial charge-transfer character,
similar to that observed for bis(4-phenylethynyl)phenyl-o-
carborane compounds (I).9 Since the computed oscillator strength
( fcalc) of the lowest energy transition in 1–4 is found to be
Experimental
General considerations
weak ( fcalc ≈ 0.1), it is likely that the transition appears as a All operations were performed under an inert nitrogen atmos-
weak shoulder or a tail in the absorption spectra (Fig. 2). The phere using the standard Schlenk and glove box techniques.
Fig. 4 HOMO and LUMO of 1–4 at the S0 geometries (isovalue = 0.04).
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Anhydrous grade solvents (Aldrich) were dried by passing solid was filtered and re-dissolved in toluene. The solution was
them through an activated alumina column and stored over purified by passing through an alumina column and the
activated molecular sieves (5 Å). Spectrophotometric-grade solvent was removed in vacuo affording 1 as a white solid.
tetrahydrofuran (THF) was used as received from Aldrich. Recrystallization from a mixed solvent of acetone–MeOH gave
Commercial reagents were used without any further purifi- 0.72 g of 1 (67.6%). Single crystals suitable for the X-ray diffrac-
cation after purchasing from Aldrich (bis(triphenylphosphine)- tion study were obtained by slow evaporation of an acetone–
palladium(II) dichloride, copper(I) iodide, diethyl sulfide, MeOH solution of 1. 1H NMR (CDCl3): δ 7.73 (s, 2 H, aryl), 7.69
triethylamine, 1,4-diiodobenzene, 1-ethynyl-3,5-bis(trifluoro- (s, 4 H, aryl), 7.27 (s, 4 H, phenylene), 3.80–1.60 (br, 20 H,
methyl)benzene,
4-ethynyl-N,N-dimethylaniline,
phenyl- B–H). 13C NMR (CDCl3): δ 132.86, 132.73, 131.13, 130.81,
acetylene, 1-butyl-4-ethynylbenzene) and KatChem (B10H14, 130.19, 124.06, 122.28, 82.99 (CB–C), 81.42 (CB–C). 11B NMR
decaborane). 2a, 2,19 and 4a24 were synthesized according to (CDCl3): δ −1.3 (br s, 4B), −9.3 (br s, 16B). Anal. Calcd for
the modified literature procedures. Deuterated solvents from C26H30B20F12: C, 39.69; H, 3.84. Found: C, 39.90; H, 3.74.
Cambridge Isotope Laboratories were used. NMR spectra of
Synthesis of 3. A procedure analogous to that for 1 was
compounds were recorded on a Bruker Avance 400 spectro- employed with decaborane (B10H14, 9.92 mmol), 3a (1.50 g,
meter (400.13 MHz for 1H, 100.62 MHz for 13C, 128.38 MHz 3.84 mmol), and Et2S (5 equiv.). Recrystallization from a mixed
for 11B) at ambient temperature. Chemical shifts are given in solvent of acetone–MeOH afforded 3 as a white solid (1.06 g,
ppm, and are referenced against external Me4Si (1H, 13C) and 44.2%). Single crystals suitable for X-ray diffraction study were
BF3·Et2O (11B). Elemental analyses were performed on an obtained by slow evaporation of an acetone–MeOH solution of
1
EA1110 (Fisons Instruments) by the Environmental Analysis 3. H NMR (CDCl3): δ 7.15 (d, J = 8.3 Hz, 4 H, phenylene), 7.09
Laboratory at KAIST. UV-vis absorption and PL spectra were (s, 4 H, aryl), 6.87 (d, J = 8.4 Hz, 4 H, aryl), 3.20–1.60 (br, 20 H,
recorded on a Jasco V-530 and a Spex Fluorog-3 Luminescence B–H) 2.49 (t, J = 7.5 Hz, 4 H, n-Bu), 1.52–1.44 (m, 4 H, n-Bu),
spectrophotometer, respectively.
1.28–1.18 (m, 4 H, n-Bu), 0.88 (t, J = 7.2 Hz, 6 H, n-Bu). 13C
Synthesis of 1a. Toluene (10 mL) and triethylamine (90 mL) NMR (CDCl3): δ 145.53, 132.57, 130.35, 130.09, 128.32, 127.56,
were added via cannula to the mixture of 1,4-diiodobenzene 85.28 (CB–C), 83.02 (CB–C), 35.01 (n-Bu), 33.14 (n-Bu), 22.13
(1.16 g, 3.52 mmol), copper(I) iodide (65 mg), and Pd- (n-Bu), 13.87 (n-Bu). 11B NMR (CDCl3): δ −2.6 (br s, 4B), −10.2
(PPh3)2Cl2 (125 mg) at room temperature. After stirring for (br s, 16B). Anal. Calcd for C30H50B20: C, 57.47; H, 8.04. Found:
15 min, 1-ethynyl-3,5-bis(trifluoromethyl)benzene (1.6 mL, C, 57.72; H, 8.28.
7.78 mmol) was added to the resulting dark brown slurry. The
Synthesis of 4. A procedure analogous to that for 1 was
reaction mixture was then stirred for 24 h. The volatiles were employed with decaborane (B10H14, 6.58 mmol), 4a (1.00 g,
removed using a rotary evaporator affording dark gray residue. 2.74 mmol), and Et2S (5 equiv.). Recrystallization from a mixed
After washing with MeOH followed by n-hexane, the remaining solvent of acetone–MeOH afforded 4 as a yellow solid (0.11 g,
solid was dried at room temperature, which afforded a sky 6.7%). Single crystals suitable for X-ray diffraction study were
blue solid (1.40 g, 72.3%). 1H NMR (THF-d8): δ 8.17 (s, 4 H, obtained by slow evaporation of a THF–MeOH solution of 4.
aryl), 8.06 (s, 2 H, aryl), 7.66 (s, 4 H, phenylene). 13C NMR 1H NMR (THF-d8): δ 7.48 (s, 4 H, phenylene), 7.35 (d, J =
(THF-d8): δ 132.84, 132.83, 132.65, 126.36, 124.16, 123.82, 8.7 Hz, 4 H, aryl), 6.61 (d, J = 8.7 Hz, 4 H, aryl), 3.08 (s, 12 H,
122.95, 92.69 (acetylene), 89.25 (acetylene). Anal. Calcd for NMe2), 3.80–1.60 (br, 20 H, B–H). 13C NMR (THF-d8): δ 152.45,
C26H10F12: C, 56.74; H, 1.83. Found: C, 56.66; H, 1.74.
133.84, 132.33, 131.32, 117.93, 111.75, 89.05 (CB–C), 85.21
Synthesis of 3a. A procedure analogous to that for 1a was (CB–C), 39.92 (NMe2). 11B NMR (THF-d8): δ −4.3, −5.6 (br s,
employed with 1,4-diiodobenzene (2.00 g, 6.06 mmol), 4B), −11.3, −12.4 (br s, 16B). Anal. Calcd for C26H44B20N2: C,
copper(I) iodide (115 mg), Pd(PPh3)2Cl2 (200 mg), and 1-butyl- 51.97; H, 7.38; N, 4.66. Found: C, 51.43; H, 7.58; N, 4.37.
4-ethynylbenzene (2.35 mL, 13.34 mmol) to afford 3a as a gray
X-ray crystallography
powder (2.08 g, 88.0%). 1H NMR (CDCl3): δ 7.47 (s, 4 H, phenyl-
ene), 7.43 (d, J = 7.9 Hz, 4 H, aryl), 7.15 (d, J = 7.9 Hz, 4 H, A specimen of suitable size and quality was coated with Para-
aryl), 2.61 (t, J = 7.4 Hz, 4 H, n-Bu), 1.63–1.55 (m, 4 H, n-Bu), tone oil and mounted onto a glass capillary. The crystallo-
1.39–1.30 (m, 4 H, n-Bu), 0.92 (t, J = 7.1 Hz, 6 H, n-Bu). 13C graphic measurement was performed using a Bruker Apex
NMR (CDCl3): δ 143.61, 131.51, 131.43, 128.50, 123.12, 120.16, II-CCD area detector diffractometer, with graphite-monochro-
91.39 (acetylene), 88.53 (acetylene), 35.61 (n-Bu), 33.37 (n-Bu), mated MoKα radiation (λ = 0.71073 Å). The structure was
22.30 (n-Bu), 13.92 (n-Bu). Anal. Calcd for C30H30: C, 92.26; H, solved by direct methods and all nonhydrogen atoms were sub-
7.74. Found: C, 91.94; H, 8.31.
jected to anisotropic refinement by full-matrix least-squares on
Synthesis of 1. This compound was prepared using an ana- F2 by using the SHELXTL/PC package.25 Hydrogen atoms were
logous method described previously.19,20 To a toluene solution placed at their geometrically calculated positions and were
(50 mL) of decaborane (B10H14, 3.27 mmol) and 1a (0.75 g, refined riding on the corresponding carbon atoms with iso-
1.69 mmol) was added an excess amount of Et2S (5 equiv.) at tropic thermal parameters. In the case of compound 1, three
room temperature. After heating to reflux, the reaction mixture fluorine atoms (F7–F9) of one CF3 group were disordered, so
was further stirred for 3 days. The solvent was removed under the fluorine atoms were partitioned. The detailed crystallo-
vacuum and MeOH (50 mL) was added. The resulting yellow graphic data are given in Table 1.
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Table 1 Crystallographic data and parameters for 1, 3, and 4
Table 3 The lowest singlet excited states for 1–4 from TD-DFT
calculationsa
Compound
1
3
4
States
S1
λcalc
fcalc
Assignment
Formula
Formula
weight
Crystal
system
Space group
a (Å)
b (Å)
c (Å)
α (°)
C
26H30B20F12
C30H50B20
626.90
C26H44B20N2
600.83
786.70
1
256.6
0.0661
HOMO−1 → LUMO (60.0%)
HOMO → LUMO (19.9%)
HOMO → LUMO (90.0%)
HOMO → LUMO (98.0%)
HOMO → LUMO (98.8%)
Monoclinic
Monoclinic
Monoclinic
2
3
4
S1
S1
S1
262.7
273.9
395.2
0.0979
0.0903
0.1218
P21
P21/n
P21/c
8.7298(5)
22.0835(12)
10.9754(6)
90
11.932(2)
13.890(2)
13.636(2)
90
17.770(4)
13.153(3)
15.181(4)
90
a Singlet energies for the vertical transition calculated at the optimized
S0 geometries.
β (°)
112.501(2)
90
1954.81(19)
2
1.337
0.109
114.132(11)
90
2062.4(6)
2
1.009
0.049
102.535(10)
90
3463.7(15)
4
1.152
0.057
γ (°)
Theoretical calculations
V (Å3)
Z
The geometries of the ground (S0) state of 1–4 were optimized
using the density functional theory (DFT) method. The elec-
tronic transition energies including electron correlation effects
were computed by the time dependent density functional
theory (TD-DFT)26 method using the B3LYP27 functional
(B3LYP). The 6-31G(d) basis set28 was used for all atoms. To
include the solvation effect of THF, the polarizable continuum
model (PCM) was used in the calculations. All calculations
were carried out using the GAUSSIAN 09 program.29
ρcalc (g cm−3
)
μ (mm−1
F(000)
T (K)
)
788
296
660
296
1256
296
Scan mode
hkl range
Multi
Multi
Multi
−10 → +10,
−25 → +24,
−12 → +12
27 490
−14 → +14,
−16 → +16,
−16 → +16
16 740
−19 → +19,
−14 → +14,
−16 → +16
38 848
Measd reflns
Unique reflns [Rint
Reflns used for
refinement
]
6038 [0.0547] 3926 [0.0394] 4825 [0.1126]
6038
3926
4825
Refined parameters
551
267
437
R1 a (I > 2σ(I))
0.0593
0.1861
1.017
0.299,
−0.268
0.0820
0.2733
1.077
0.557,
−0.335
0.0488
0.1441
1.012
0.156,
−0.188
wR2 b all data
Conclusions
GOF on F2
ρfin (max/min) (e Å−3
)
1,4-Di-o-carborane substituted benzene compounds (1–4), in
which aryl-o-carborane cages are introduced at the 1 and 4
positions of phenylene ring, were prepared and characterized.
The electronic variation of the substituent on the appended
aryl group at the C1-position of o-carborane led to the color
tuning of the aggregation-induced emission. Experimental and
theoretical calculation results suggested that intramolecular
“through-space” charge transfer occurs between the appended
aryl group (HOMO) and the central phenylene ring (LUMO),
and the greater change in the HOMO level by the substituent
than that in the LUMO is responsible for the emission color
tuning. The results in this study indicate that the emission
color of the o-carborane-containing luminophores can also be
tuned by changing the appended aryl group of o-carborane.
a R1 = ∑||Fo| − |Fc||/∑|Fo|. b wR2 = {[∑w(Fo2 − Fc2)2]/[∑w(Fo2)2]}1/2
.
Table 2 UV-vis absorption and PL data for 1–4
λabs/nma
λem/nm
298 Kb 77 Kb Solid Filmc THF–H2Od
(ε × 10−3
/
Compound M−1 cm−1
)
1
2
3
4
212 (44.7),
—
—
—
—
510
520
539
639
483
521
509
625
506
520
521
616
478
513
511
631
238 (30.4)
211 (39.4),
223 (34.0)
210 (42.1),
231 (46.5)
210 (41.5),
238 (32.0),
286 (31.7)
Acknowledgements
a Measured in degassed THF (ca. 2 × 10−5 M). b Measured in degassed
THF (5 × 10−5 M). c Spin-coated PMMA film with 1–4 (10 wt%). d In
THF–H2O = 1 : 99 (v/v). λexc = 324 nm for 1; 325 nm for 2; 333 nm for 3;
360 nm for 4.
This work was supported by the Basic Science Research
Program (no. 2012039773 for M. H. Lee) and the Priority
Research Centers program (no. 2009-0093818 for M. H. Lee)
through the National Research Foundation of Korea (NRF).
Computational resources for this work were provided by the
KISTI (KSC-2012-C2-42).
UV-vis absorption and PL measurements
The solution UV-vis absorption and PL measurements were
performed in degassed THF with a 1 cm quartz cuvette. PL
measurements were also carried out under various conditions,
such as at 77 K, in the film state, and in the neat solid state.
The detailed conditions are given in Table 2.
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