Regulating Circularly Polarized Luminescence Signals of Chiral

Article pubs.acs.org/Macromolecules

Regulating Circularly Polarized Luminescence Signals of Chiral Binaphthyl-Based Conjugated Polymers by Tuning Dihedral Angles of Binaphthyl Moieties Yuxiang Wang, Yunzhi Li, Shuai Liu, Fei Li, Chengjian Zhu, Shuhua Li,* and Yixiang Cheng* Key Lab of Mesoscopic Chemistry of MOE, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210046, P. R. China S Supporting Information *

ABSTRACT: A series of chiral binaphthyl-based conjugated polymers enantiomers incorporating boron dipyrromethene (BODIPY) chromophore in the main chain backbone were designed and synthesized by Pd-catalyzed Sonogashira crosscoupling reaction. All of them can exhibit strong Cotton effects and circularly polarized luminescence (CPL) emission signals in THF solution. The CD absorption dissymmetry factors (gabs) and the luminescence dissymmetry factors (glum) can be regulated by tuning the dihedral angles of binaphthyl arising from different substitutions of BINOL hydroxyls. Interestingly, the chiral polymers can exhibit the gradual increase of both gabs and glum as the decrease of dihedral angles of the chiral binaphthyl moiety. This work can provide a new strategy for the development of CPL emission materials.

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fluorescence sensors, dye-sensitized solar cells, bioprobes, and so on.30−36 But chiral BODIPY derivatives or chiral BODIPYbased conjugated polymers as CPL emission materials have been rarely repoted.20,37−39 De la Moya first reported an achiral BODIPY-based chromophore which could produce CPL signal induced from the perturbation of chiral BINOL moiety.38 Recently, our group also synthesized chiral BINOL-based OBODIPY enantiomers incorporating aggregation-induced emission (AIE) active groups, and the intramolecular energy transfer from AIE-active donors to O-BODIPY acceptors resulted in the red-color CPL emission.40 Among the reported axial chiral molecules, optically active 1,1′-binaphthol (BINOL) derivatives have received particular interest due to their versatile backbone which can be modified at the well-defined molecular level. These chiral binaphthyl derivatives have been widely applied for enantioselective recognition and asymmetric catalysis system.41−45 Moreover, chiral binaphthyl-based polymers can also be developed as potential CPL emission materials due to their effective and stable chiral structures. Recently, we first discovered that (R)binaphthyl-based AIE-active chiral conjugated polymers which polymerized only at 3,3′-positions of binaphthyl can show aggregation-induced CPL emission.46 Meanwhile, our group designed and synthesized several chiral binaphthyl-based AIE molecules with reversal CPL response behaviors from solution to aggregation due to the different dihedral angles of binaphthyl moiety via the transfer of cis-/trans-conformation.47 Imai’s

INTRODUCTION The differential emission of left- and right-circularly polarized light from chiral nonracemic luminescent systems, which is called as circularly polarized luminescence (CPL), has now become an active research field.1−4 In the past few decades, much attention has been devoted to the CPL emission materials of the chiral organic fluorescence molecules due to its potential application in photoelectric devices5,6 and its pivotal role in studying the chiral feature of the emitting excited states.7−11 Normally, luminescence dissymmetry factor (glum) is used to evaluate the level of CPL emission by using the equation glum = 2(IL − IR)/(IL + IR) = 2ΔI/I; herein IL and IR represent the emission intensities of left and right circularly polarized luminescence, respectively.12,13 Recently, chiral conjugated fluorescent polymers have been regarded as more and more promising CPL materials because of their easy preparation, tunable luminescent properties, and the welldefined backbone modification.14−21 However, as far as we know, there have been few reports on tunable CPL glum values of chiral conjugated polymers. Therefore, developing scientific methods that can effectively tune the glum values of CPL materials by changing the chiral conjugated polymer chain backbone structures is of great significance. As an excellent organic fluorophore, boron dipyrromethene (BODIPY) and its derivatives have been widely applied for optical devices due to its several advantages, such as tunable emission wavelength, high absorption coefficients, high emission quantum yields a narrow absorption band, etc.22−29 In the past decade, near-infrared (NIR) emissive conjugated polymers incorporating BODIPY chromophore have been widely used as building blocks for energy-transfer cassettes, © XXXX American Chemical Society

Received: April 27, 2016 Revised: July 20, 2016

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DOI: 10.1021/acs.macromol.6b00883 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules Scheme 1. Synthesis Procedures of Monomers and the Chiral Polymers

spectropolarimeter. Fluorescence spectra were obtained from a Hitachi F-7000 florescence spectrophotometer. Circularly polarized luminescence (CPL) spectra were performed on a JASCO CPL-200 spectrofluoropolarimeter. In the CPL measurements, the excitation wavelength was 310 nm, scan speed was 200 nm/min, number of scans was 3, and slit width was 3000 μm. Molecular weight was measured by gel permeation chromatography (GPC) with a Waters-244 HPLC pump (polystyrene as standards and THF as solvent). Thermogravimetric analyses (TGA) were obtained from a PerkinElmer Pyris-1 instrument under a N2 atmosphere. Synthesis of R/S-M1. 3,3′-Diiodo-1,1′-binaphthalene-2,2′-diol (1.0 g, 1.86 mmol) and K2CO3 (2.57 g, 18.6 mmol) were added to 100 mL of dry, degassed DMF, and the mixture was stirred for 15 min at 80 °C under argon. A solution of 1,3-bis(bromomethyl)benzene (638 mg, 2.42 mmol) in 10 mL of anhydrous DMF was added to the reaction mixture via a syringe pump over 16 h. After injection, the reaction mixture was cooled to room temperature and then filtered to remove K2CO3. After the solvent was evaporated, the residue was purified by column chromatography to give compound R/S-M1 as a white solid. R/S-M1: 202 mg, 17%. 1H NMR (400 MHz, CDCl3): δ 8.46 (s, 2H), 7.66 (d, J = 8.0 Hz, 2H), 7.35 (t, J = 7.3 Hz, 2H), 7.31− 7.27 (m, 2H), 7.14 (d, J = 8.5 Hz, 2H), 7.05 (d, J = 6.6 Hz, 3H), 6.98− 6.91 (m, 1H), 5.76 (d, J = 11.6 Hz, 2H), 4.87 (d, J = 11.6 Hz, 2H). 13C NMR (100 MHz, CDCl3): δ 150.00, 140.24, 135.08, 131.74, 131.00,

group also found that chiral binaphthyl-based organic molecules could show reversal CPL signals by tuning the dihedral angles of chiral binaphthyl moiety from acute angles to obtuse angles via different substitutions of BINOL hydroxyls or dispersed-state changes.48−51 To the best of our knowledge, so far there have been no reports on tunable CPL signals of chiral conjugated polymers by changing the dihedral angles of binaphthyl moieties. In this paper, we designed and synthesized three kinds of chiral binaphthyl-based conjugated polymer enantiomers which can exhibit the tunable glum values of CPL emission signals by changing the dihedral angles of binaphthyl moieties regulated by different substitutions of BINOL hydroxyls.

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EXPERIMENTAL SECTION

Measurements and Materials. All the solvents and reagents were commercially available and analytical grade. THF and Et3N were distilled from sodium in the presence of benzophenone. A Bruker 400 spectrometer was used to measure NMR spectra, which were at 400 MHz for 1H NMR and 100 MHz for 13C NMR and reported as parts per million (ppm) from the internal standard TMS. UV−vis spectra and circular dichroism (CD) spectra were recorded on a JASCO J-810 B


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mixture was stirred at 72 °C under a N2 atmosphere for 3 days. After the reaction was finished, the solution was filtered through a short silica gel column, and the solvent was evaporated under reduced pressure. Then the residues were dissolved in 2 mL of dichloromethane and precipitated in 50 mL of methanol. The obtained solids was filtered and further washed by using 2 × 10 mL of methanol. Then the solids were dried under vacuum, and R/S-P3 can be collected as dark purple solids. R/S-P3: 141 mg, 65%. GPC: Mw = 15 250, Mn = 10 520, PDI = 1.45. 1H NMR (400 MHz, CDCl3): 8.13 (s), 7.87 (s), 7.44 (br), 7.28 (br), 7.09−7.02 (m), 5.75 (s), 3.98 (s), 2.77 (s), 1.65 (s), 1.56 (s), 1.16 (br), 0.76 (br).

129.97, 128.13, 127.28, 127.26, 125.83, 125.68, 125.57, 124.56, 89.97, 74.54. MS (ESI, m/z): 678.85 (M+ + 39). [α]25 D of R/S-M1 (c = 1.0, THF) are +180.0/−172.0. Synthesis of R/S-M2. 3,3′-Diiodo-1,1′-binaphthalene-2,2′-diol (500 mg, 0.93 mmol), 1-bromobutane (318 mg, 2.32 mmol), and K2CO3 (1.28 g, 9.3 mmol) were added to 20 mL of CH3CN, and the mixture was stirred for 10 h at 80 °C. After the reaction mixture was cooled to room temperature, the solution was filtered. The solvent was evaporated, and the residue was purified by silica gel column chromatography (eluent: petroleum ether (60−90 °C)/ethyl acetate, v/v, 50:1) to give R/S-M2 as white solid. R/S-M2: 550 mg, 91%. 1H NMR (400 MHz, CDCl3): δ 8.51 (s, 2H), 7.78 (d, J = 8.2 Hz, 2H), 7.39 (t, J = 7.5 Hz, 2H), 7.26 (t, J = 7.5 Hz, 2H), 7.11 (d, J = 8.5 Hz, 2H), 3.80 (dt, J = 8.6, 6.1 Hz, 2H), 3.30 (dt, J = 8.5, 6.7 Hz, 2H), 1.34−1.16 (m, 4H), 0.98−0.85 (m, 2H), 0.78−0.65 (m, 2H), 0.50 (t, J = 7.4 Hz, 6H). 13C NMR (100 MHz, CDCl3): δ 154.24, 139.66, 134.06, 132.15, 127.03, 127.01, 126.03, 125.71, 125.54, 93.16, 73.44, 31.78, 18.69, 13.58. MS (ESI, m/z): 668.00 (M+ + 18), [α]25 D of R/SM2 (c = 1.0, THF) are −79.0/+74.0. Synthesis of R/S-M3. 2,2′-Methylenedioxy-1,1′-binaphthyl (1.0 g, 3.35 mmol) was dissolved in 30 mL of anhydrous Et2O; 5.4 mL of nBuLi (2.5 mol/L in hexane, 13.41 mmol) was added by syringe injection at 0 °C under an Ar atmosphere. The reaction mixture was stirred at room temperature for 2 h, and then iodine (4.25 g, 16.76 mmol) was added to the reaction mixture at −78 °C under an Ar atmosphere. The mixture was then stirred overnight after the solution was gradually warmed to room temperature. The reaction mixture was quenched by a saturated NaHSO3 solution. The water phase was extracted with ethyl acetate (2 × 50 mL); the combined organic layers were washed with water and brine twice and dried with anhydrous Na2SO4. The solvent was evaporated, and the residue was purified by silica gel column chromatography (eluent: petroleum ether (60−90 °C)/ethyl acetate, v/v, 30:1) to give R/S-M3 as light yellow solid. R/ S-M3: 590 mg, 32%. 1H NMR (300 MHz, CDCl3): δ 8.51 (s, 2H), 7.83 (d, J = 8.2 Hz, 2H), 7.46 (td, J = 8.1, 6.7, 1.3 Hz, 2H), 7.40 (d, J = 8.1 Hz, 2H), 7.35−7.27 (m, 2H), 5.68 (s, 2H). 13C NMR (100 MHz, CDCl3): δ 149.63, 139.70, 133.10, 131.86, 127.39, 126.85, 126.75, 126.56, 125.98, 102.05, 89.99. [α]25 D of R/S-M3 (c = 1.0, THF) are −550.0/+534.0. Synthesis of R/S-P1. R/S-M1 (150.0 mg, 0.23 mmol), M4 (117.2 mg, 0.23 mmol), CuI (4.5 mg, 0.02 mmol), and Pd(PPh3)4 (27.1 mg, 0.02 mmol) were dissolved in 10 mL of THF and 5 mL of Et3N. The mixture was stirred at 72 °C under a N2 atmosphere for 3 days. After the reaction was finished, the solution was filtered through a short silica gel column, and the solvent was evaporated under reduced pressure. And then the residues were dissolved in 2 mL of dichloromethane and precipitated in 50 mL of methanol. The obtained solids was filtered and further washed by using 2 × 10 mL of methanol. Then the solids were dried under vacuum, and R/S-P1 can be collected as dark purple solids. R/S-P1: 151 mg, 73%. GPC: Mw = 13 350, Mn = 8910, PDI = 1.50. 1H NMR (400 MHz, CDCl3): 8.53 (s), 8.03 (s), 7.71 (t), 7.49 (t), 7.35−6.96 (m), 5.88 (d), 4.97 (d), 4.01 (t), 2.88 (s), 1.76 (s), 1.20 (br), 0.81 (t). Synthesis of R/S-P2. R/S-M2 (200.0 mg, 0.31 mmol), M4 (153.9 mg, 0.31 mmol), CuI (5.9 mg, 0.03 mmol), and Pd(PPh3)4 (35.5 mg, 0.03 mmol) were dissolved in 10 mL of THF and 5 mL of Et3N. The mixture was stirred at 72 °C under a N2 atmosphere for 3 days. After the reaction was finished, the solution was filtered through a short silica gel column and the solvent was evaporated under reduced pressure. Then the residues were dissolved in 2 mL of dichloromethane and precipitated in 50 mL of methanol. The obtained solids was filtered and further washed by using 2 × 10 mL of methanol. Then the solids were dried under vacuum, and R/S-P2 can be collected as dark purple solids. R/S-P2: 223 mg, 81%. GPC: Mw = 11 730, Mn = 8460, PDI = 1.39. 1H NMR (400 MHz, CDCl3): 8.09 (s), 7.80 (t), 7.46 (t), 7.36 (t), 7.22 (t), 7.13 (t), 6.98 (d), 4.03 (t), 3.96 (t), 3.70 (br), 2.76 (s), 1.63 (s), 1.56 (s), 1.18 (br), 0.81 (t), 0.41 (t). Synthesis of R/S-P3. R/S-M3 (150.0 mg, 0.27 mmol), M4 (136.4 mg, 0.27 mmol), CuI (5.2 mg, 0.03 mmol), and Pd(PPh3)4 (31.5 mg, 0.03 mmol) were dissolved in 10 mL of THF and 5 mL of Et3N. The

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RESULTS AND DISCUSSION The detailed synthesis procedures of the chiral polymers are given in Scheme 1. R/S-1, 2, and M4 could be prepared according to the reported literatures.52−54 The chiral polymers R/S-P1, P2, and P3 were synthesized by Pd-catalyzed Sonogashira coupling reaction of R/S-M1, M2, and M3 with M4, respectively. As listed in Table 1, the resulting polymers Table 1. Yields, GPC Data, and Thermal Properties of the Polymers

P1 P2 P3

yield (%)

Mwa (g mol−1)

Mna (g mol−1)

PDIa (Mw/Mn)

Tdb (°C)

73 81 65

13350 11730 15250

8910 8460 10520

1.50 1.39 1.45

320 290 340

a

Molecular weight was determined by GPC with a Waters-244 HPLC pump (polystyrene as standards and THF as solvent). bDegradation temperature (Td) was obtained from a PerkinElmer Pyris-1 instrument under the N2 atmosphere.

have good yields and medium molecular weights. As shown in the 1H NMR spectra of R/S-P1, P2, and P3 (Figures S11− S13), it can be clearly observed that the single peak situated at 3.3 ppm disappears, which can demonstrate the effective polymerization of the monomers. The thermogravimetric analysis (TGA) curves reveal that all these polymers have high degradation temperature (Td) of 5% weight loss above 280 °C (Figure S1), indicating that these polymers are of good stability and can be applied for CPL emission or optoelectronic materials. These chiral polymers could be collected in dark purple solids and are stable in air. And they can also show good solubility in CH2Cl2, CHCl3, DMF, and THF, which can be due to the nonplanar polymer backbone structure and the flexible n-octyl group substituents of BODIPY chromophore. The absorption and fluorescence emission spectra of the monomer M4 and three chiral polymers were tested in THF solution (1.0 × 10−5 mol/L corresponding to the BODIPY moiety). As shown in Figure 1, the absorption and emission spectra of P1, P2, and P3 have little distinction due to their similar polymer backbone structures. The monomer molecule M4 exhibits a strong absorption peak at 542 nm and a weak absorption peak at 385 nm, which can be ascribed to π−π* transitions of BODIPY. But the chiral polymers P1, P2, and P3 have four absorption peaks in UV−vis spectra. The two peaks at 280 and 340 nm can be assigned to the binaphthyl moiety, and the peak at 410 nm can be regarded as the π−π* transition of the BODIPY moiety with a 25 nm red-shift. Compared with the monomer molecule chromophore M4, the maximal and strongest absorption wavelength λmax appears red-shifted as high as 50, 43, and 37 nm for P1, P2, and P3, respectively, which can be attributed to the extended π-conjugation structure C


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Figure 2. CD spectra of R/S-P1, P2, and P3 (1.0 × 10−5 mol/L in THF).

same, which indicates that dihedral angle of binaphthyl can produce great influence on Cotton effect of chiral conjugated polymer backbone system. Herein, R/S-P1 (1,3-bis(methylene)benzene-substituted polymers) has the minimal | gabs| value (0.0012); on the contrary, R/S-P3 (methylenesubstituted polymers) has the maximal |gabs| value (0.0027), which is about 2.3-fold of the minimal |gabs| values of R/S-P1. CD spectra only show the chirality of chiral polymers in the ground state, and the dihedral angle changes of binaphthyl can lead to obvious differences from gabs of three chiral polymers. Therefore, we further investigated the chiral feature of three chiral conjugated polymers in the excited states, which may produce circularly polarized luminescence (CPL) emission signal changes. Herein, we performed CPL emission determination of three chiral polymer enantiomers (1.0 × 10−5 mol/L corresponding to the BODIPY moiety in THF) by using JASCO CPL-200. As is evident from Figure 3, we can observe

Figure 1. (a) UV−vis absorption spectra; (b) fluorescence spectra of M4 and P1, P2, and P3 (1.0 × 10−5 mol/L in THF, λex = 310 nm); inset: photographs taken under UV illumination (365 nm).

between chiral binaphthyl moiety and BODIPY.20,55−58 Moreover, it can be clearly observed that the conjugated polymers exhibit broader absorption peaks than M4 because of the extended conjugated structure. As is evident from Figure 1b, the fluorescence spectrum of the monomer M4 has a sharp emission peak at 561 nm, while the maximal emission peaks of P1 (627 nm), P2 (625 nm), and P3 (622 nm) are red-shifted for 66, 64, and 61 nm, respectively. The red-color emission of these chiral polymers can also be ascribed to the extended πconjugated in the polymer backbone structure. The fluorescence quantum yields of these chiral polymers are 0.23 (P1), 0.21 (P2), and 0.26 (P3), respectively, indicating these chiral polymers are excellent red-color luminescent emission materials (inset of Figure 1b). In this paper we carried out the CD spectra of R/S-P1, P2, and P3 in THF solution. As is evident from Figure 2, three chiral polymers show similar Cotton effects due to the same conjugated polymer backbone. Meanwhile we can also observe that R/S-P1, P2, and P3 can exhibit mirror-image CD band. The strong Cotton effects at 250 and 280 nm in the short wavelength region can be assigned to the characteristic absorption of chiral binaphthyl moieties in the polymer main chain.21,59−61 Interestingly, three chiral polymers show the strongest Cotton effect at about 600 nm of the long wavelength region, which can be regarded as absorption bands of the extended π-conjugation chiral polymer structure and also demonstrate that the chirality of the binaphthyl moiety can effectively induce the whole conjugation polymer backbone and form the chromophore BODIPY-based chiral conjugated polymers. Most importantly, we also found there are obvious differences from the absorption dissymmetry factor (gabs) of R/ S-P1, P2, and P3 at the wavelengths of the maximal CD signals although their conjugated polymer backbone structures are the

Figure 3. CPL spectra of R/S-P1, P2, and P3 (1.0 × 10−5 mol/L in THF, λex = 310 nm).

that all R/S-P1, P2, and P3 enantiomers can exhibit clear mirror-image CPL signals, and their emission wavelengths of CPL signals can well correspond with their fluorescent emission wavelengths for P1 (627 nm), P2 (625 nm), and P3 (622 nm), respectively. Most interestingly, we also find that the luminescence dissymmetry factors (glum) of three chiral polymers are coincident with the absorption dissymmetry factor (gabs) of CD spectra from chiral conjugated polymer backbone structure, which further demonstrates that the D


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S1 state are about 109.9°, 78.8°, and 56.0°, which are similar to those in the corresponding ground states. The dihedral angle θ value differences can be attributed to the diverse steric hindrance of chiral binaphthyl groups in M1, M2, and M3. The calculated vertical excitation energies Ex, parameters DS and RS, and the absorption and emission dissymmetry factors gx are listed in Table S1. The data in Table S1 demonstrate that the designed chiral binaphthyl groups have obvious influence on the ECD and CPL properties by changing the gx of three model molecules. The obtained emission dissymmetry factor glum of M3 is about 0.23 × 10−3 cgs, which is about 1.5 and 1.1 times larger than that of M1 (0.15 × 10−3 cgs) and M2 (0.21 × 10−3 cgs), respectively. We can also find that the calculated value gx decreases as the dihedral angles θ value increases, which is in line with the experimental results. Thus, our calculations confirm that the ECD and CPL signals of chiral conjugated polymers can be regulated by tuning dihedral angles of the binaphthyl moiety. However, BINOL-based small molecules generated reversal CPL signals as the dihedral angles of chiral binaphthyl is tuned from acute angles to obtuse angles.48−51 In this paper we found that the dihedral angles change of chiral binaphthyl can effectively tune the glum values of CPL emission signals of the chiral conjugated polymers. This observation is different from that observed for chiral binaphthyl-based small molecules. We assume that the luminescence polarization direction of the CPL signal depends on the chiral configurations of the binaphthylbased conjugated polymers, but the glum values can be changed by the dihedral angles of the chiral binaphthyl moiety.

chirality transfer of the binaphthyl moiety can not only affect Cotton effect of the conjugation polymer backbone but also directly change glum values of CPL emission signals (Table 2). Table 2. gabs and glum of P1, P2, and P3 λabs (nm) S-P1 R-P1 S-P2 R-P2 S-P3 R-P3

593 592 585 585 579 579

gabsa (λ/nm) 0.0012 −0.0012 0.0025 −0.0025 0.0027 −0.0029

(602) (603) (601) (600) (594) (594)

λem (nm) 627 627 624 625 622 622

glumb (λ/nm) 0.0010 −0.0009 0.0018 −0.0018 0.0021 −0.0020

(626) (629) (621) (621) (611) (611)

a Absorption dissymmetry factors (gabs) of the chiral polymers at the wavelength in the parentheses. bLuminescence dissymmetry factors (glum) of the chiral polymers at the wavelength in the parentheses.

Therefore, we can draw the conclusion that the dihedral angle of chiral binaphthyl regulated by different substitutions of BINOL hydroxyls can control the chirality transfer effect from chiral binaphthyl moiety to the whole conjugation polymer backbone structure. In addition, the |glum| values of R/S-P1, P2, and P3 are 0.001−0.002, which lies in the range of most purely organic CPL materials from 10−5 to 10−2.62−67 In order to fully understand the unique CPL emission behaviors of the chiral polymers, we performed a series of ab initio calculations on three model molecules (M1, M2, and M3), which should be good to mimic three chiral polymers: SP1, S-P2, and S-P3, respectively (Figure 4). The ground-state

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CONCLUSIONS In summary, these designed chiral polymers can show strong CD absorption and CPL response signals owing to effective chirality transfer from the chiral binaphthyl moiety to the whole conjugation polymer backbone structure. CD absorption dissymmetry factors (gabs) and luminescence dissymmetry factors (glum) of chiral binaphthyl-based polymers can be regulated by tuning the dihedral angle of chiral binaphthyl moiety. The results of this work can develop a new strategy for the design of red color CPL emission materials.

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Figure 4. Optimized structures of the first excited-state (S1) and the corresponding dihedral angle θ values of two naphthyl rings in M1, M2, and M3. For comparison, the corresponding dihedral angle θ values in the ground state (S0) are also shown.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.6b00883. TGA curve of the chiral polymers; relevant calculation results; 1H NMR, 13C NMR, and MS spectra of all new compounds (PDF)

geometries (S0) of three model systems were optimized at the B3LYP/6-31G(d,p) level. The relevant first excited-state (S1) structures were then optimized with the time-dependent DFT (TD-DFT) method at the same theory level as described above. Based on the optimized S1 structures, electronic circular dichroism (ECD) and CPL calculations of three model molecules were carried out at the TD-B3LYP/6-311+G(d,p) level. Finally, the absorption and emission dissymmetry factors gx can be calculated with the equation gx = 4RS/DS,68−70 where RS is the rotational strength and DS is the dipole strength in either absorption (ECD) or emission (CPL) state. In this paper, all calculations were performed with the Gaussian 09 package.71 The optimized structures of the first excited state (S1) and the corresponding dihedral angle θ values of two naphthyl rings in M1, M2, and M3 are presented in Figure 4. It is evident from Figure 4 that the obtained θ values of M1, M2, and M3 in the

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AUTHOR INFORMATION

Corresponding Authors

*E-mail [email protected]; Tel +86-25-89686508 (Y.C.). *E-mail [email protected]; Tel +86-25-89686465 (S.L.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful to Prof. Zhiyong Tang and Dr. Lin Shi at NCNST for assistant in CPL measurement. Ab initio calculations were performed at the Shenzhen Supercomputer Center (SSC, China). This work was supported by the National E


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