Noticeable Chiral Center Dependence of Signs and Magnitudes in

Article Cite This: Macromolecules XXXX, XXX, XXX−XXX

Noticeable Chiral Center Dependence of Signs and Magnitudes in Circular Dichroism (CD) and Circularly Polarized Luminescence (CPL) Spectra of all-trans-Poly(9,9-dialkylfluorene-2,7-vinylene)s Bearing Chiral Alkyl Side Chains in Solution, Aggregates, and Thin Films Takumi Yamada,† Kotohiro Nomura,*,† and Michiya Fujiki*,‡ †

Department of Chemistry, Tokyo Metropolitan University, 1-1 Minami Osawa, Hachioji, Tokyo 192-0397, Japan Graduate School of Materials Science, Nara Institute of Science and Technology (NAIST), 8916-5 Takayama, Ikoma, Nara 630-0101, Japan

‡

S Supporting Information *

ABSTRACT: Effects of chiral alkyl side chains in poly(9,9-dialkylfluorene-2,7-vinylene)s [PFVs, (S)-3-methylpentyl (3mpe), (S)-4methylhexyl (4mhex), (S)-5-methylheptyl (5mhep), (S)-6-methyloctyl (6moct), and (S)-3,7-dimethyloctyl (dmo)] toward aggregation-induced circular dichroism (AICD) and circularly polarized luminescence (AICPL) and CD/CPL spectra in solution and in thin film have been explored. The (all-trans) PFV samples with similar conjugation repeat units containing well-defined (vinyl) end groups were prepared by acyclic diene metathesis polymerization using Ru catalyst. The PFV aggregates, prepared in situ in a mixed solution of CHCl3/MeOH, showed clear CD signals ascribed to AICD, whereas these samples showed CD-silent in the CHCl3 solution. The absolute magnitude (gCD value) was affected by the chiral side chains (without obey the even−odd rule) and increased in the order 3mpe, 5mhep < 4mhex < dmo < 6mcot. Both the 6-moct and dmo aggregates showed clear CPL signals ascribed to AICPL, whereas signals of the others were not obvious. The λmax values in the UV−vis spectra red-shifted depending upon kind of alkyl side chains due to formation of J-type aggregates. These results suggest that the optically active aggregates adopt certain helical supramolecular ordered structures induced by an interpolymer interaction through chain entanglement. The gCD values in the drop casted thin film (prepared from the CHCl3 solution) were lower than those in the aggregates, and the value increased in the order 5mhep, dmo < 4mhex, 6mcot < 3mpe. The λmax values in their UV−vis spectra red-shifted but were not affected by the side chain. These results suggest that supramolecular structures formed by aggregate and film are different, and the formation in film could be induced by an interpolymer π-stacking. In contrast, the basic characteristics were preserved in the thin film prepared from the PFV-6moct aggregate (CHCl3/MeOH); the film showed high both gCD and gCPL values close to those in the original aggregate.

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INTRODUCTION Conjugated polymers (CPs) are promising semiconducting materials applied for solution processable electronic, photonic, and optoelectronic devices.1−7 Recently, an importance of precision (defect-free nature) in the synthesis has been widely recognized7 because their device performances are strongly affected by defect (such as halogen, sulfur embedded in main chain, sp3-type main chain structures, regio-/stereoirregularity, unintended cross-linking, etc.), which should diminish the mobility of charged carriers, quench luminescence, and act as deep level traps of charged carriers. It has also been recognized that their properties are affected by the end group,8,9 as demonstrated in the end-functionalized poly(fluorene)s10−17 and poly(9,9-dialkyl-fluorene-2,7-vinylene)s (PFVs).18−23 A rational designdevelopment of new method/methodology for synthesis of defect-free and high molecular weight π-CPs with well-defined end groupshas thus been considered as an important subject. © XXXX American Chemical Society

Moreover, it has also been known that their fundamental properties are affected by the supramolecular interactions (such as noncovalent intermolecular π−π, CH/π, and van der Waals interactions, dipole−dipole, hydrogen bonding, etc.) and the nano/mesoscale organization;24−26 in particular, the electronic communication between distinct polymer chains (interchain interaction) is essential for light emission and charge transport.27−29 In the recent years, several optically active π-CPs carrying chiral alkyl side chains30−34 are a growing interest because of their circular dichroism (CD)30−36 and circularly polarized luminescence (CPL)37,38 properties in the UV−vis−nearinfrared region. CD and CPL spectra signify the ground state (S0) chirality35,36 and the lowest photoexcited state (S1) Received: February 1, 2018 Revised: March 5, 2018

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DOI: 10.1021/acs.macromol.8b00241 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules Scheme 1. Acyclic Diene Metathesis (ADMET) Polymerization for Synthesis of Poly(arylene vinylene)s52,53

chirality,37,38 respectively, and provide useful information for the conformational analysis of chiral molecules and polymers. Moreover, greatly magnified CD and CPL signals with their desired signs are applicable to several potent chiroptical applications, such as sensing, display, security ink, switching, memory, and resolution.40−44 However, the absolute gCD and gCPL magnitudes and their chiroptical signs of CD/CPL relative to the corresponding nonpolarized UV−vis/photoluminescence (PL) signals in homogeneous solutions are on the order of 10−4, meaning that the degree of circular polarization is only 0.01%. One can give rise several open questions to whether chiroptical signs and magnitude between CD and CPL spectra are identical for each (i) in homogeneous solution, (ii) as aggregate form in poorer solvents, and (iii) in the thin solid films or not. However, the comprehensive study of stereogenic center dependence affecting CD/CPL spectral characteristics in a series of defect-free, well-defined (controlled molecular weight, conjugation repeat units as well as end groups) πconjugated polymers containing different chiral side chains (concerning formation of in solution, supramolecular aggregates, and in thin films) have never been reported so far.30−34,45−50 The acyclic diene metathesis (ADMET) polymerization approach (Scheme 1)19−23,51−64 has been known as a beneficial method for synthesis of high molecular weight PFVs, poly(2,5dialkyl-phenylene-1,4-vinylene)s (PPVs), and poly(N-alkylcarbazole-2,7-vinylene)s.21−23,52,53,56 This is because that the approach not only affords defect-free, stereoregular (all-trans) materials that are difficult by adopting the conventional condensation approaches (dehalogenation−condensation, etc.) but also enables synthesis of the π-CPs with well-defined (vinyl) chain ends.19−23,52,53,56,65,66 The remaining vinyl termini are inert to luminescent characteristics, and a facile, exclusive end-functionalization can be achieved by combined olefin metathesis with Mo−alkylidene followed by Wittig-type cleavage with aldehyde.19−23,65,66 This paper highlights synthesis of a series of defect-free, welldefined PFVs [with all-trans stereoregularity, controlled molecular weights (conjugation repeat units) and end groups] carrying different chiral alkyl side chains (Chart 1) by the ADMET polymerization.67,68 We wish to demonstrate that optically active all-trans PFVs revealed a noticeable chiral center position dependence of signs and magnitudes in their CD/CPL

Chart 1. Poly(9,9-dialkylfluorene-2,7-vinylene)s (PFVs) Containing Chiral Alkyl Side Chains Employed in This Study

spectra when these PFVs exist especially in aggregates and in the thin solid films. As far as we know, this is the first comprehensive study concerning effect of chiral alkyl group in π-CPs toward the optical properties, and the study should provide a rational materials design of π-CPs in terms of the supramolecular interactions and the communication with distinct polymer chains.69,70

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RESULTS AND DISCUSSION Synthesis of Poly(9,9-dialkylfluorene-2,7-vinylene)s (PFVs) Containing Chiral Alkyl Side Chains. A series of 2,7-divinylfluorenes (DVFs) containing two chiral alkyl side chains [(S)-2-methylbutyl (2mb), (S)-3-methylpentyl (3mpe), (S)-4-methylhexyl (4mhex), (S)-5-methylheptyl (5mhep), (S)6-methyloctyl (6moct), and (R)- or (S)-3,7-dimethyloctyl (dmo)] in the 9 positions were prepared from the corresponding dibromide, which were obtained by treating the alkyl bromide (RBr) with 2,7-dibromofluorene in DMSO,52,71−73 by Stille coupling reactions with (CH2 CH)SnnBu3 in the presence of Pd(PPh3)4 (Scheme 2).51,52,73 A series of alkyl bromides (RBr), except commercially available (S)-(+)-1-bromo-2-methylbutane, were prepared from the corresponding alcohols.73 These compounds were identified B


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(runs 5−8, Mn(GPC) = 18 500−45 700, Mw/Mn = 1.41−2.12),74 as reported previously in synthesis of poly(9,9-di-n-octylfluorene-2,7-vinylene)s.18−20,51,52,56,65 However, the resultant polymers became insoluble when the polymerizations of DVFs containing 2mb, 3mpe, and (R)-dmo were conducted under the same conditions. Therefore, these polymerizations were conducted under low concentrations or in CH2Cl2 and THF for obtainment of high molecular weight polymers (runs 1−4, and 9, Table 1). In order to conduct measurement of (to discuss the chiral position effect of chiroptical characteristics in) circular dichroism (CD) and circularly polarized luminescence (CPL) spectroscopy of the PFV samples with similar molecular weights [degree of polymerization (DPn), conjugation repeat units], sample preparations were conducted under modified conditions summarized in Table 2 (experimental details are shown in the Supporting Information).73 The resultant PFVs possessed high stereoregularity (all-trans) with well-defined chain ends (vinyl group), as demonstrated by PFVs containing n-hexyl, 2′-ethylhexyl, and n-octyl side chains;52 good relationships between Mn(NMR) values (estimated by integration ratios in 1H NMR spectra on the basis of vinyl end groups) and Mn(calcd) values [estimated by GPC data vs polystyrene standards, Mn(calcd) = Mn(GPC)/1.6]74 were seen in all cases. Circular Dichroism (CD) and Circularly Polarized Luminescence (CPL) Spectra of Poly(9,9-dialkylfluorene-2,7-vinylene)s (PFVs) Containing Chiral Alkyl Side Chains in Solution, Aggregates, and Thin Film. CD/UV− Vis Spectral Characteristics of Poly(9,9-dialkylfluorene-2,7vinylene)s (PFVs) Containing Chiral Alkyl Side Chain in CHCl3 Solution and CHCl3−MeOH Cosolvents. Figure 1 shows circular dichroism (CD) and UV−vis spectra (1.0 × 10−6 M at 25 °C) for PFVs containing chiral alkyl side chains [(S)-3methylpentyl (3mpe), (S)-4-methylhexyl (4mhex), (S)-5methylheptyl (5mhep), (S)-6-methyloctyl (6moct), and (S)3,7-dimethyloctyl (dmo)] in CHCl3 solution and aggregates dispersed in MeOH−CHCl3 with optimized volume fractions [which provides the highest gCD values, ratio of CHCl3/MeOH = 15/85 (v/v) except 1/19 (3mpe) and 25/75 (dmo); detailed spectra data with different volume ratios are shown in the Supporting Information].75 These aggregates were prepared by adding MeOH slowly into the CHCl3 solution until the desired final volume ratio. The spectra for poly(9,9-di-n-octylfluorene2,7-vinylene)51,52 are also shown for comparison.

Scheme 2. Synthesis of PFVs Containing Chiral Alkyl Side Chains

by NMR spectra, APCI-MS, and elemental analysis (detailed synthetic procedure and data for their identifications are shown in the Supporting Information).73 Acyclic diene metathesis (ADMET) polymerization of a series of DVFs were conducted at 50 °C using a sealed Schlenk tube equipped with a high-vacuum valve in toluene or dichloromethane in the presence of Ru(CHPh)Cl2(IMesH2)(PCy3) [IMesH2 = 1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene, Cy = cyclohexyl].52 As reported previously,51−53 continuous removal of ethylene from the mixture is important for obtainment of the high molecular weight polymers in this condensation polymerization; the solution was thus placed in vacuo for a certain period. The results are summarized in Table 1. The ADMET polymerization of DVFs [containing 4mhex, 5mhep, 6moct, and (S)-dmo] afforded high molecular polymers with uniform molecular weight distributions in most cases

Table 1. Acyclic Diene Metathesis (ADMET) Polymerization of 9,9-Dialkyl-2,7-divinylfluorenes (DVFs) Containing Chiral Alkyl Side Chains; Synthesis of High Molecular Weight Poly(9,9-Dialkylfluorene-2,7-vinylene)s (PFVs) under Optimized Conditionsa run

R

solvent

concb/M

time/h

yieldc/%

Mn(NMR)d × 10−4

Mn(GPC)e × 10−4

Mn(calcd)f × 10−4

Mw/Mne

1 2 3 4 5 6 7 8 9

2mb 2mb 3mpe 3mpe 4mhex 5mhep 6moct (S)-dmo (R)-dmo

toluene THF toluene CH2Cl2 toluene toluene toluene toluene toluene

0.20 0.20 0.20 0.20 0.40 0.40 0.40 0.40 0.20h

8 24 24 24 24 24 24 24 24

99 71 75 99 92 97 99 99 99

0.29 0.43 0.66 1.20 2.20 1.99 3.06 2.79 0.85

0.43 0.65 1.15g 1.85 3.31 2.78 4.57 3.95 1.36

0.27 0.41 0.72 1.15 2.01 1.73 2.86 2.47 0.85

1.22 1.63 1.71 1.41 2.09 1.92 1.81 2.12 1.67

Conditions: Ru catalyst (2.5 mol %), 50 °C. bInitial DVF concentration in mmol/mL. cIsolated yield as MeOH fraction. dEstimated by 1H NMR spectra (on the basis of vinyl chain ends). eGPC data in THF vs polystyrene standards at 40 ◦C. fCorrected value, Mn(calcd) = Mn(GPC)/1.6.74 gPartly insoluble in toluene. hBecame insoluble in toluene under highinitial monomer concentration (0.40 M). a

C


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Table 2. Synthesis of Analysis Sample of Poly(9,9-Dialkylfluorene-2,7-vinylene)s (PFVs) Containing Chiral Alkyl Side Chains by ADMET Polymerizationa R

solvent

concb/M

time/h

yieldc/%

Mn(NMR)d × 10−4

Mn(GPC)e × 10−4

Mn(calcd)f × 10−4

Mw/Mne

DPng

2mb 3mpe 4mhex 5mhep 6moct (S)-dmo (R)-dmo

THF CH2Cl2 toluene toluene toluene toluene toluene

0.20 0.20 0.40 0.40 0.40 0.40 0.20

24 24 8 24 8 24 24

71 77 97 83 99 98 99

0.43 0.59 0.79 0.84 0.90 0.95 0.85

0.65 0.93 1.29 1.32 1.48 1.45 1.36

0.41 0.58 0.81 0.82 0.93 0.90 0.85

1.63 1.49 1.80 1.84 1.64 1.68 1.67

11.4 15.3 19.0 19.1 19.1 19.0 17.0

Conditions: Ru catalyst (2.5 mol %), 50 °C. bInitial DVF concentration in mmol/mL. cIsolated yield as MeOH fraction. dEstimated by 1H NMR spectra (on the basis of vinyl chain ends). eGPC data in THF vs polystyrene standards at 40 °C. fCorrected value, Mn(calcd) = Mn(GPC)/1.6.74 gDPn = number-average degree of polymerization. a

1730 cm−1 from the S0 ← S1 state are observed in the fluorescence spectra (described below, Figure 3b). These energy spacings are related to stretching vibration modes of trans CC bonds, and a very small Stokes’s shift (∼475 cm−1) indicates no significant reorganization of PFV backbone in the photoexcited state. all-trans-PFVs with chiral side chains synthesized newly adopt an inherently rigid framework in the S0 and S1 states, though substantial rotational freedom along C−C bonds should be remained. These results led us to conclude that as demonstrated previously,52 no significant alterations of PFV main chain in dilute CHCl3 solution are observed in their UV−vis spectra for the resultant PFVs with different alkyl groups in the 9,9′-position. Note that, in contrast, all the aggregates of PFV with different chiral side chains showed clear exciton couplet-like signals in π−π* transition region ascribed to aggregation-induced circular dichroism (AICD, supramolecular polymerization behaviors) in the π−π* transitions.39,45,68,77−80 However, any CD signals were not detectable (CD silent) in the CHCl3 solution, indicating left−right inducing capability by the chiral substituent should be inefficient because both main chain and side chains are labile conformationally in CHCl3; chiral side chains at 9,9-positions do not perturb directly electronically and conformationally to the main chain in their S0 and S1 states. These behaviors arise from a low rotational barrier (1.5 kcal mol−1 per C−C single bond between fluorene ring and transvinylene groups) according to a previous DFT calculations.67 It also turned out that the absolute magnitudes and sign of AICD couplet (gCD values) were affected by the relative volume ratios of CHCl3/MeOH (the detailed analysis data, spectra are shown in the Supporting Information).75 These CD-active aggregates from seven PFVs adopt certain helically ordered supramolecular assemblies with helps of chiral side chains, and noncovalent interactions between the chiral side chains and between the chiral side chain and PFV main chain are responsible for emerging CD signals. To efficiently store the CD-active state, the high rotational barrier height (along the multiple C−C single bonds, possibly, greater than 20 kcal mol−1) permits us to efficiently induce an imbalance between left- and right-hand helical states. Noncovalent interactions between the chiral side chains and between the chiral side chain and PFV main chain are thus responsible for emerging CD signals. As expected, no detectable CD signal of poly(9,9-di-noctylfluorene-2,7-vinylene) was observed (shown below) because the gCD value is Kuhn’s dimensionless anisotropy ratio.35,36 It is thus clear that these optically active aggregates adopt certain helically ordered supramolecular assemblies induced by the chiral side chains.

Figure 1. CD and UV−vis spectra (concentration 1.0 × 10−6 M in CHCl3 or CHCl3/MeOH at 25 °C) for PFVs containing chiral side chains [(S)-3-methylpentyl (3mpe), (S)-4-methylhexyl (4mhex), (S)5-methylheptyl (5mhep), (S)-6-methyloctyl (6moct), and (S)-3,7dimethyloctyl (dmo)]. (a) CD and (b) UV−vis spectra in CHCl3/ MeOH [under optimized conditions, 15/85 (v/v) except 1/19 (3mpe) and 25/75 (dmo)]75 and (c) CD and UV−vis spectra in CHCl3 solution. Detailed analysis data are shown in the Supporting Information.75

As reported previously in the UV−vis spectra of PFV (in solution),21,22,51,52,56,65 three absorption bands (λmax = 400, 427, and 455 nm, Figure 1c) with an energy spacing of 1440− 1580 cm−1 are attributed to π−π* transitions of the S0 → S1 state with electron−phonon coupling that are characteristic of all-trans-PFV backbone.76,77 These absorption peaks at 455, 427, and 400 nm are attributed to 0−0, 0−1, and 0−2 transitions, respectively,77 and the corresponding emission peaks at 465, 496, and 530 nm with an energy spacing of 905− D


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Macromolecules It should be noted that the absolute magnitude of the CD signals (gCD value at 470 nm) was affected by the chiral side chains, and the gCD value at the first Cotton band under the optimized conditions in each PFVs increased in the order 3mpe (4.19 × 10−3) ≈ 5mhep (−7.25 × 10−3) < 4mhex (2.91 × 10−2) < S-dmo (−3.27 × 10−2) < 6mcot (−1.10 × 10−1). The trend could suggest that formation of these helical aggregates would be induced by the chiral side chain through chain entanglement. Noticeably, unexpected findings are the facts that gCD values at 470 nm and their CD signs do not obey a simple odd−even effect that are often reported in several chiral nematic liquid crystals and several aggregates of π-CPs with chiral substituents.39,40,44 Although all six chiral alkyl side chains are commonly (S)chirality, the magnitudes of PFVs containing 3mpe and 5mhep are weak and sign inversions (positive-sign) of AICD couplet were observed in PFVs containing 3mpe and 4mhex. The facts could suggest that formation of these aggregates would be induced by a weak intermolecular interaction of polymer chains; it may be speculated that achiral branching at the 7position may swap a preference of chirality in the aggregates. It turned out in Figure 1b that λmax values of the aggregates prepared in situ in a mixed solution of CHCl3/MeOH showed red-shifts in all cases, depending upon kind of alkyl side chains employed, compared to those in the CHCl3 solution. The results clearly suggest formation of J-type aggregates due to π−π* interactions under these conditions; these tendencies are affected by the kind of chiral side chains employed. CD/UV−Vis Spectral Characteristics in THF Solution and THF−MeOH Cosolvents. Similarly, AICD signals were observed in the aggregates prepared in situ by pouring MeOH slowly into the THF solution with certain ratios (v/ v), whereas CD signals were not detectable in the THF solution (Figure S2-1).75 Three distinct vibronic 0−0 (470 nm), 0−1 (437 nm), and 0−2 (405 nm) bands with an energy spacing of 1810−1900 cm−1 are obvious (Figure S2-2).75 However, in contrast to the spectra in CHCl3/MeOH, the gCD value (under the optimized solvent ratios) was not strongly affected by the chiral side chain employed except that the magnitude in PFV containing 6moct side chain was very weak (detailed data are shown in the Supporting Information, Figure S2-2).75 Moreover, no significant differences (in both the λmax values the relative intensities) in the UV−vis spectra were observed for the aggregates prepared in situ of THF/MeOH (Figure S2-2).75 At this moment, we have no clear reasons to explain this difference (solvent effect). A clear couplet-like AICD spectra with an almost ideal mirror-image (similar gCD values) with similar UV−vis spectra were observed in the aggregates formed in PFVs containing (R)- and (S)-dmo (Figure 2a, THF/MeOH = 35/65 in v/v), clearly suggesting that as described above, these optically active aggregates adopt certain helical supramolecular ordered structures induced by the chiral side chain. It was also revealed that a sign inversion of AICD couplet was also observed by changing the solvent ratios (sample with 6moct side chain in THF-MeOH, Figure 2b), although the magnitudes (gCD values) were very weak (low). Since their UV−vis spectra were apparently different from those prepared in CHCl3/MeOH, this could be assumed due to different aggregation behavior. A sign inversion (with low gCD values) was also observed by changing the solvent (CHCl3 vs THF) in the sample with (S)4mhex (Figure 2c), whereas these showed similar UV−vis spectra.

Figure 2. CD and UV−vis spectra (concentration 1.0 × 10−6 M at 25 °C) for PFVs containing (a) (R)- or (S)-3,7-dimethyloctyl (dmo) in THF/MeOH (35/65 in v/v), (b) (S)-6-methyloctyl (6moct) in THF−MeOH with different ratios, and (c) (S)-4-methylhexyl (4mhex) in CHCl3−MeOH or THF−MeOH (15/85 in v/v). Detailed analysis data are shown in the Supporting Information.75

CPL/PL Spectral Characteristics in CHCl3 Solution and CHCl3−MeOH Cosolvents. Figure 3 shows circularly polarized luminescence (CPL) and photoluminescence (PL, fluorescence) spectra (concentration 1.0 × 10−6 M in CHCl3 or CHCl3/MeOH at 25 °C, excitation at 380−390 nm) for PFVs containing chiral alkyl side chains in CHCl3 solution (Figure 3b) and aggregates prepared by pouring MeOH slowly into the CHCl3 solution [Figure 3a, highest gCPL (and gCD) values prepared under optimized ratio of CHCl3/MeOH = 15/85 (v/ v) except 1/19 (3mpe) and 25/75 (dmo); detailed spectra data with different ratios are shown in the Supporting Information].75 It should be noted that some PFV aggregates, especially containing 6moct and S-dmo side chains, prepared in situ in a mixed solution of CHCl3/MeOH, showed clear CPL signals ascribed to aggregation-induced circularly polarized luminescence (AICPL and CPL by supramolecular polymerization), whereas the magnitudes in their CPL signals in CHCl3 solution were apparently weak. The absolute magnitudes of AICPL couplet, |gCPL|, were also affected by the volume ratios of E


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position, and the gCPL value increased in the order 5mhep, 4mhex < dmo (Figure S2-3).75 As observed in the CD spectra in THF/MeOH, the magnitude of PFV aggregates containing the 6mcot side chain, which showed the largest gCPL value in CHCl3/MeOH (Figure 3a), was negligible; we have no clear reason to explain the difference at this moment, as described above. As observed in CHCl3/MeOH, their relative intensities of the λmax values (emission peaks at ca. 440, 465, and 496 nm) in the PL spectra were affected by nature of alkyl side chains employed, whereas no significant differences were observed in their PL spectra in the THF solution. A clear sign inversion with similar PL spectra as well as similar gCPL values was observed in the aggregates formed in PFVs containing (R)- and (S)-dmo (Figure S2-3),75 clearly suggesting that as described above these optically active aggregates adopt certain helical supramolecular ordered structures induced by the chiral chain ends. Clear sign inversions of AICPL couplet were not observed even by varying the CHCl3/MeOH or THF/MeOH ratios. These results also clearly suggest a formation of supramolecular structures induced by chiral side chain by interpolymer interaction, especially by entanglement of the polymer side chain. Interestingly, as shown in Figure 3b, these PFVs reveal clearly two or three well-resolved, weak vibronic CPL signals with negative sign associated with three well-resolved PL spectra in CHCl3 solution [gCPL (at 465 nm): (−1.0 to −0.6) × 10−3], although all five chiral PFVs in CHCl3 solution are CDsilent with well-resolved UV−vis π−π* bands. These chiral PFVs in the photoexcited state in homogeneous solution would prevail a handed helical motif with (−)-CPL sign because a greater energetically imbalance between P and M states at the first photoexcited S1 state happens. This would be an interesting contrast to the fact that the chiral PFVs in the ground state exist as a random mixture of P- and M-helical motifs in fluidic solution probably due to a rotational freedom along C−C bonds that enables a low barrier height between P and M states. At the moment, whether minus-sign CD/CPL is M or P is not unclear. CD/UV−Vis and CPL/PL Spectral Characteristics in the Thin Solid Film. Figure 4 shows CD and UV−vis spectra (at 25 °C) of PFV films (after annealing) prepared by the drop-casting method. These samples were prepared from the CHCl3 solution (1.0 × 10−5 mol/L) by casting onto quartz substrate placed in Petri dish, and the resultant films were dried (before annealing, data are shown in the Supporting Information)75,81 and were then placed into a vacuum oven for 4 h at 60 °C (first annealing, spectral data are shown in the Supporting Information)75 and then 2 h at 80 °C (sample used as after annealing).75,81 It should be noted that the absolute magnitude of the CD signal (gCD value) was affected by the chiral side chains, and the gCD value (after second annealing) increased in the order 5mhep, dmo < 4mhex, 6mcot < 3mpe. PFV containing 3mpe showed the large gCD value with sign inversion of AICD couplet. In contrast, no significant differences in the λmax values were observed in their UV−vis spectra, whereas these λmax values showed red-shifts (and became broad compared to those in solution, Figure 5) due to formation of J-type aggregates by π−π* interactions under these conditions. These results suggest that these helical aggregates would not be induced by the chiral side chain through the chain entanglement, but by interpolymer π-stacking (because no significant differences were observed in the UV−vis spectra).

Figure 3. CPL and fluorescence (PL) spectra (concentration 1.0 × 10−6 M in CHCl3 or CHCl3/MeOH at 25 °C) for PFVs containing chiral side chains [(S)-3-methylpentyl (3mpe), (S)-4-methylhexyl (4mhex), (S)-5-methylheptyl (5mhep), (S)-6-methyloctyl (6moct), and (S)-3,7-dimethyloctyl (dmo)]. (a) CD and UV−vis spectra in CHCl3/MeOH [under optimized conditions, 15/85 (v/v) except 1/19 (3mpe) and 25/75 (dmo); data with different ratios are shown in the Supporting Information]75 and (b) CD and UV−vis spectra in CHCl3 solution. Detailed analysis data are shown in the Supporting Information.75

CHCl3/MeOH (detailed data are shown in the Supporting Information).75 It turned out that the gCPL value in the PFV aggregates was affected by the chiral side chains. Both 6moct and S-dmo clearly reveal three well-resolved negative-sign vibronic CPL signals associated with three-well resolved vibronic PL bands at 465 nm (0−0), 496 nm (0−1), and 530 nm (0−2), with an energy spacing of 1290−1340 cm−1, and the gCPL value of 6moct is exceptionally boosted as large as −4.7 × 10−2, and that of Sdmo is enhanced to −1.0 × 10−2. However, CPL signals from other aggregates made of 3mpe, 4-mhex, and 5mhep are not obvious, and significant sign inversions (by varying the solvent ratios) were not observed. The relative intensities of the λmax values (emission peaks at ca. 440, 465, and 496 nm) in these aggregates were affected by nature of alkyl side chains, whereas no significant differences (in both the λmax values the relative intensities) were observed in their PL spectra in CHCl3 solution in all cases. The results clearly suggest that formation of supramolecular structures induced by chiral side chain by interpolymer interaction, especially by entanglement of the polymer side chain. Similarly, some CPL signals, ascribed to AICPL, were clearly observed in the aggregates prepared in situ by pouring MeOH slowly into the THF solution with certain ratios (v/v), whereas the magnitudes in some CPL signals in THF solution were apparently weak (Figure S2-1);75 the gCPL values were affected by the volume ratios of THF/MeOH (Figure S2-3, detailed data are shown in the Supporting Information).75 The gCPL value was also affected by the chiral side chains in the 9F


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signal close to that in the aggregate prepared in situ from CHCl3/MeOH solution,75 and the λmax values and the relative intensity in the UV−vis spectrum was also close to that in the aggregate (Figure 5, right). The gCD value in the film prepared from the aggregate (blue line) was apparently larger than that in the film prepared from CHCl3 solution (dashed red lined). The results thus clearly indicate that the basic characteristics in the original aggregate were preserved in the thin film prepared from the PFV-6moct aggregate. Figure 6 shows selected CPL and PL spectra of PFV samples (containing chiral 3mpe, 6moct, and dmo side chains) in aggregates (prepared from CHCl3/MeOH) and in thin films (after annealing). As described above (Figure 3), the absolute magnitude of the CPL signals (gCPL value) was affected by the chiral side chains, and the aggregates containing 6moct and Sdmo side chains showed clear CPL signals ascribed to aggregation-induced circularly polarized luminescence (AICPL), whereas signals in the other aggregates (3mpe, 4mhex, and 5mhep) were not obvious. These suggest that formation of these helical aggregates would be induced by the chiral side chain through chain entanglement. It turned out from Figure 6 that PFV samples containing chiral 6moct and 3mpe showed apparent CPL signals (more data are shown in Figure S2-6),75 whereas gCPL value for the sample film containing dmo side chain showed negligible. The observed trend would be somewhat similar to that observed in CD spectra with PFV film (Figure 4). However, the gCPL value especially in PFV with 6moct in film was low compared to that in the aggregate (Figure 6). Moreover, an emission peak observed at ca. 440 nm in the PL spectra in PFV aggregates was not observed in those in the PFV films; no significant differences in the λmax values as well as the relative intensities were observed.75 These would also suggest that supramolecular structures formed by aggregate and film were different, which also means that a driving force for formation of supramolecular structures should be different. In contrast, as observed in Figure 5 (right), the drop-casted thin film prepared from the aggregate containing 6moct side chain showed clear and strong CPL signal, which is relatively close to that in the aggregate prepared in situ from CHCl3/ MeOH solution (Figure 6 right); the λmax values and the relative intensity in the PL spectrum were also close to those in

Figure 4. CD and UV−vis spectra (in film prepared by drop-cast, at 25 °C) for PFVs containing chiral side chains [(S)-3-methylpentyl (3mpe), (S)-4-methylhexyl (4mhex), (S)-5-methylheptyl (5mhep), (S)-6-methyloctyl (6moct), and (S)-3,7-dimethyloctyl (dmo)]. Detailed analysis data are shown in the Supporting Information.75

This means that driving force for formation of supramolecular structure should be different between the aggregates (prepared in situ from CHCl3/MeOH) and films after annealing. However, note that as shown in Figure 5 (left), the magnitudes of AICD couplet (gCD values) in films (dotted line) after annealing are apparently lower than those in aggregates (line in plain). These gCD valus are apparently lower than those in polyfluorenes containing chiral side chains.45,46 Also note that the UV−vis spectra (λmax values) of each sample in solution, aggregates (prepared from CHCl3/MeOH), and films (after annealing) are apparently different. These clearly suggest that the observed difference should be due to formation of supramolecular structure in different manner (especially between aggregate and film). In contrast, importantly, the drop-casted thin film prepared from the aggregate containing 6moct side chain showed CD

Figure 5. Left: selected CD and UV−vis spectra for PFV aggregates containing chiral side chains [(S)-3-methylpentyl (3mpe), (S)-4-methylhexyl (4mhex), and (S)-6-methyloctyl (6moct)] prepared in situ from CHCl3−MeOH solution (line in plain) or thin film (prepared by the drop-cast method from CHCl3 solution, in dashed line). Right: CD and UV−vis spectra for PFV-6moct aggregates or drop-casted thin films prepared from CHCl3 solution (dashed line) or aggregate (blue, line in plain). G


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Figure 6. Left: selected CPL and fluorescence (PL) spectra for PFVs containing chiral side chains [(S)-3-methylpentyl (3mpe), (S)-6-methyloctyl (6moct), and (S)-3,7-dimethyloctyl (dmo) prepared in situ from CHCl3−MeOH solution (line in plain) or thin film (prepared by the drop-cast method from CHCl3 solution, in dashed line). Right: CPL and fluorescence (PL) spectra for PFV-6moct aggregates or drop-casted thin films prepared from CHCl3 solution (dashed line) or aggregate (blue, line in plain).

the aggregate. Moreover, the gCPL value in the film prepared from the aggregate (blue line) was larger than that in the film prepared from CHCl3 solution (dashed red lined). The results thus also clearly indicate that the basic characteristics in the original aggregate could be preserved in the thin film prepared from the PFV−6moct aggregate.

side chains. These results also suggest that formation of supramolecular structures was induced by chiral side chain through interpolymer interaction, especially by the entanglement of the polymer side chain. Interestingly, these PFVs showed well-resolved vibronic CPL signals in CHCl3, although their magnitudes were very low and these are CD-silent in solution. The gCD value in the PFV thin film (prepared by the dropcast method from the CHCl3 solution) was affected by the chiral side chains employed, and the value (after second annealing) increased in the order 5mhep, dmo < 4mhex, 6mcot < 3mpe. No significant differences in the λmax values were observed in their UV−vis spectra, whereas these λmax values showed red-shifts (and became broad compared to those in solution) due to formation of J-type aggregates. Although the magnitudes (gCD values) are low compared to those in the aggregates (prepared from CHCl3/MeOH), supramolecular structures formed by aggregate and film were different, which means that formation of the structure in film would be induced by induced by π-stacking, not by the chain entanglement in the chiral side chain. PFV films containing chiral 6moct and 3mpe showed apparent CPL signals, but the gCPL value especially in PFV with 6moct was low compared to that in aggregate; no significant differences in the λmax values as well as the relative intensities were observed. These would also suggest the above assumption concerning the driving force for formation of the helical ordered structures. In contrast, the basic characteristics (signals in the CD and CPL spectra and λmax values and their relative intensities in the UV−vis and PL spectra) were preserved in the thin film prepared from the PFV-6moct aggregate (CHCl3/MeOH); the film showed high both gCD and gCPL values close to those in the original aggregate. We have demonstrated that a driving force for formation of supramolecular structures should be different between aggregates (prepared in situ by pouring poor solvent into solution) and films (prepared by the drop-cast method). It is clearly demonstrated that nature of the chiral side chain in PFV plays an important role to form helical supramolecular structures. As described in the Introduction, it has been known that the fundamental properties in π-conjugated polymers are affected by the supramolecular interactions, and

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SUMMARY We have prepared a series of (all-trans, defect free) poly(9,9dialkyl-fluorene-2,7-vinylene)s (PFVs) containing chiral alkyl side chains [(S)-3-methylpentyl (3mpe), (S)-4-methylhexyl (4mhex), (S)-5-methylheptyl (5mhep), (S)-6-methyloctyl (6moct), and (S)-3,7-dimethyloctyl (dmo)], which possess similar conjugation repeat units with well-defined (vinyl) end groups by acyclic diene metathesis (ADMET) polymerization using Ru catalyst. All the PFV aggregates, prepared in situ in a mixed solution of CHCl3/MeOH, showed clear exciton couplet-like signals ascribed to aggregation-induced circular dichroism (AICD, supramolecular polymerization behaviors), whereas any CD signals were not detectable in CHCl3 solution and in the PFV aggregate containing achiral n-octyl side chain. The absolute magnitude of the CD signals (gCD value) was affected by the chiral side chains, and the gCD value increased in the order 3mpe, 5mhep < 4mhex < dmo < 6mcot. The order does not obey the odd−even rule that is often reported in several chiral nematic liquid crystals and several aggregates of CPs with chiral substituents. Moreover, the λmax values in the UV−vis spectra showed red-shifts, depending upon kind of alkyl side chains employed, due to formation of J-type aggregates through π−π* interactions. The results clearly suggest that these optically active aggregates adopt certain helical supramolecular ordered structures induced by an intermolecular interaction through chain entanglement. Both the 6-moct and the dmo PFV aggregates showed clear CPL signals ascribed to aggregation-induced circularly polarized luminescence (AICPL), whereas signals of PFV containing the other side chains (3mpe, 4mhex, and 5mhep) were not obvious. The corresponding PL spectra in the aggregates became broad compared to those in solution, and the relative intensities of the λmax values in these aggregates were affected by nature of alkyl H


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Macromolecules as far as we know, this is the first comprehensive study concerning effect of the chiral side chains including demonstration of a driving force [chain entanglement (aggregates) or π-stacking (thin flim)] for formation of the (helical) supramolecular structures (J-type aggregates). We highly believe the fact that this research shall provide important basic information and shall contribute a better understanding for design of conjugated materials for the desired purpose.

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(8) Park, J. K.; Jo, J.; Seo, J. H.; Moon, J. S.; Park, Y. D.; Lee, K.; Heeger, A. J.; Bazan, G. C. End-Capping Effect of a Narrow Bandgap Conjugated Polymer on Bulk Heterojunction Solar Cells. Adv. Mater. 2011, 23 (21), 2430−2435. (9) Wang, Q.; Zhang, B.; Liu, L.; Chen, Y.; Qu, Y.; Zhang, X.; Yang, J.; Xie, Z.; Geng, Y.; Wang, L.; Wang, F. Effect of End Groups on Optoelectronic Properties of Poly(9,9-dioctylfluorene): A Study with Hexadecylfluorenes as Model Polymers. J. Phys. Chem. C 2012, 116 (41), 21727−21733. (10) Miteva, T.; Meisel, A.; Knoll, W.; Nothofer, H. G.; Scherf, U.; Müller, D. C.; Meerholz, K.; Yasuda, A.; Neher, D. Improving the Performance of Polyfluorene-Based Organic Light-Emitting Diodes via End-capping. Adv. Mater. 2001, 13 (8), 565−570. (11) Ego, C.; Marsitzky, D.; Becker, S.; Zhang, J.; Grimsdale, A. C.; Müllen, K.; MacKenzie, J. D.; Silva, C.; Friend, R. H. Attaching Perylene Dyes to Polyfluorene: Three Simple, Efficient Methods for Facile Color Tuning of Light-Emitting Polymers. J. Am. Chem. Soc. 2003, 125 (2), 437−443. (12) Gong, X.; Ma, W.; Ostrowski, J. C.; Bechgaard, K.; Bazan, G. C.; Heeger, A. J.; Xiao, S.; Moses, D. End-Capping as a Method for Improving Carrier Injection in Electrophosphorescent Light-Emitting Diodes. Adv. Funct. Mater. 2004, 14 (4), 393−397. (13) Burrows, H. D.; Seixas de Melo, J.; Forster, M.; Güntner, R.; Scherf, U.; Monkman, A. P.; Navaratnam, S. Hole Formation and Transfer in Poly[9,9-di(ethylhexyl)fluorene] and an Amine EndCapped Derivative in Solution. Chem. Phys. Lett. 2004, 385 (1−2), 105−110. (14) Beljonne, D.; Pourtois, G.; Silva, C.; Hennebicq, E.; Herz, L. M.; Friend, R. H.; Scholes, G. D.; Setayesh, S.; Müllen, K.; Brédas, J. L. Interchain vs. Intrachain Energy Transfer in Acceptor-Capped Conjugated Polymers. Proc. Natl. Acad. Sci. U. S. A. 2002, 99 (17), 10982−10987. (15) Asaoka, S.; Takeda, N.; Iyoda, T.; Cook, A. R.; Miller, J. R. Electron and Hole Transport To Trap Groups at the Ends of Conjugated Polyfluorenes. J. Am. Chem. Soc. 2008, 130 (36), 11912− 11920. (16) El-Khouly, M. E.; Chen, Y.; Zhuang, X.; Fukuzumi, S. LongLived Charge-Separated Configuration of a Push−Pull Archetype of Disperse Red 1 End-Capped Poly[9,9-bis(4-diphenylaminophenyl)fluorene]. J. Am. Chem. Soc. 2009, 131 (18), 6370−6371. (17) Shibano, Y.; Imahori, H.; Sreearunothai, P.; Cook, A. R.; Miller, J. R. Conjugated “Molecular Wire” for Excitons. J. Phys. Chem. Lett. 2010, 1 (9), 1492−1496. (18) Kuwabara, S.; Yamamoto, N.; Sharma, P. M. V.; Takamizu, K.; Fujiki, M.; Geerts, Y.; Nomura, K. Precise Synthesis of Poly(fluorene2,7-vinylene)s Containing Oligo(thiophene)s at the Chain Ends: Unique Emission Properties by the End Functionalization. Macromolecules 2011, 44 (10), 3705−3711. (19) Takamizu, K.; Inagaki, A.; Nomura, K. Precise Synthesis of Poly(fluorene vinylene)s Capped with Chromophores: Efficient Fluorescent Polymers Modified by Conjugation Length and EndGroups. ACS Macro Lett. 2013, 2 (11), 980−984. (20) Fushimi, Y.; Koinuma, M.; Yasuda, Y.; Nomura, K.; Asano, M. S. Effects of end-groups on photophysical properties of poly(9,9-di-noctylfluorene-2,7-vinylene)s linked with metalloporphyrins: Synthesis and time-resolved fluorescence spectroscopy. Macromolecules 2017, 50 (5), 1803−1814. (21) Miyashita, T.; Inagaki, A.; Nomura, K. One-pot synthesis of endfunctionalized conjugated polymers by combined acyclic diene metathesis (ADMET) polymerization using molybdenum catalyst with Wittig-type coupling. J. Jpn. Pet. Inst. 2016, 59 (5), 197−203. (22) Miyashita, T.; Kunisawa, M.; Sueki, S.; Nomura, K. Synthesis of poly(arylene vinylene)s with different end groups by combining acyclic diene metathesis polymerization with Wittig-type couplings. Angew. Chem., Int. Ed. 2017, 56 (19), 5288−5293. (23) Chen, Y.; Abdellatif, M. M.; Nomura, K. Olefin metathesis polymerization: Some recent developments in the precise polymerizations for synthesis of advanced materials (by ROMP, ADMET). Tetrahedron 2018, 74 (6), 619−643.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.8b00241. Experimental procedure for synthesis of 9,9-dialkyl-2,7divinylfluorene and polymer samples, preparation of analysis samples, selected NMR spectra, additional CD and CPL spectra (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*Tel & fax +81-42-677-2547; e-mail [email protected] (K.N.). *Tel +81-743-72-6040, fax +81-743-72-6049, e-mail fujikim@ ms.naist.jp (M.F.). ORCID

Kotohiro Nomura: 0000-0003-3661-6328 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The project is partly supported by Advanced Catalytic T r a n s f o r m a t i o n f o r C a r b o n u t i l iz a t io n ( A C T - C JPMJCR12YX), Japan Science and Technology Agency (JST), Japan. K.N. and T.Y. express their thanks to Dr. S. Sueki (Tokyo Metropolitan University, TMU) for experimental assistance (for synthesis of DFVs) and Profs. Akiko Inagaki and Ken Tsutsumi (TMU) for helpful discussions. K.N. expresses his thanks to Prof. Y. H. Geerts (Université Libre de Bruxelles, ULB) for fruitful discussions.

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Macromolecules (62) Selected recent reviews for ADMET polymerization (refs 62−64); see: Lehman, S. E., Jr.; Wagener, K. B. In Handbook of Metathesis; Grubbs, R. H., Ed.; Wiley-VCH: Weinheim, 2003; Vol. 3, pp 283−312. (63) Atallah, P.; Wagener, K. B.; Schulz, M. D. ADMET: The Future Revealed. Macromolecules 2013, 46 (12), 4735−4741. (64) Schulz, M. D.; Wagener, K. B. In Handbook of Metathesis, 2nd ed.; Grubbs, R. H., Khosravi, E., Eds.; Wiley-VCH: Weinheim, 2015; Vol. 3, pp 313 − 355. (65) Nomura, K.; Yamamoto, N.; Ito, R.; Fujiki, M.; Geerts, Y. Exclusive End Functionalization of All trans-Poly(fluorene vinylene)s Prepared by Acyclic Diene Metathesis Polymerization: Facile Efficient Synthesis of Amphiphilic Triblock Copolymers by Grafting Poly(ethylene glycol). Macromolecules 2008, 41 (12), 4245−4249. (66) Abdellatif, M. M.; Nomura, K. Precise Synthesis of Amphiphilic Multiblock Copolymers by Combination of Acyclic Diene Metathesis (ADMET) Polymerization with Atom Transfer Radical Polymerization (ATRP) and Click Chemistry. ACS Macro Lett. 2012, 1 (3), 423−427. (67) Fujiki, M.; Jalilah, A. J.; Suzuki, N.; Taguchi, M.; Zhang, W.; Abdellatif, M. M.; Nomura, K. Chiral optofluidics: Gigantic circularly polarized light enhancement of all-trans-poly(9,9-di-n-octylfluorene2,7-vinylene) during mirror-symmetry-breaking aggregation by optically tuning fluidic media. RSC Adv. 2012, 2 (16), 6663−6671. Formation of chiral aggregate from trans-poly(9,9-di-n-octylfluorene2,7-vinylene) upon addition of (R)- and (S)-limonene in CHCl3− MeOH, whereas poly[(9,9-di-n-octylfluoren-2,7-diyl)-alt-yleneethynylene] (PFE) did not show any CD signals under the same conditions. (68) Yorsaeng, S.; Kato, Y.; Tsutsumi, K.; Inagaki, A.; Kitiyanan, B.; Fujiki, M.; Nomura, K. Synthesis of well-defined oligo(2,5-dialkoxy1,4-phenylene vinylene)s with chiral end groups: Unique helical aggregations induced by the chiral chain ends. Chem. - Eur. J. 2015, 21 (47), 16764−16768. Comprehensive study concerning effect of both end groups and conjugation repeat units toward helical aggregations induced by the chiral chain ends, in well-defined oligo(2,5-dialkoxy1,4-phenylene vinylene)s with chiral end groups. Effect of vinyl end groups toward the helical aggregation can be considered as negligible. (69) Examples (review) for aggregation induced emission:39 Mei, J.; Leung, N. L. C. R.; Kwok, T. K.; Lam, J. W. Y.; Tang, B. Z. Aggregation-Induced Emission: Together We Shine, United We Soar! Chem. Rev. 2015, 115 (21), 11718−11940. (70) Example (review) for supramolecular helical systems: Yashima, E.; Ousaka, N.; Taura, D.; Shimomura, K.; Ikai, T.; Maeda, K. Supramolecular Helical Systems: Helical Assemblies of Small Molecules, Foldamers, and Polymers with Chiral Amplification and Their Functions. Chem. Rev. 2016, 116 (22), 13752−13990. (71) Woo, E. P.; Shiang, W. R.; Roof, G. R.; Inbasekaran, M. The Dow Chemical Co. International Patent Application WO 97/05184, 1997. 2,7-Aryl-9-substituted fluorenes and 9-substituted fluorene oligomers and polymers. (72) Related synthesis (introduction of alkyl side chains according to ref 71); for examples see: Marsitzky, D.; Vestberg, R.; Blainey, P.; Tang, B. T.; Hawker, C. J.; Carter, K. R. Self-Encapsulation of Poly2,7-fluorenes in a Dendrimer Matrix. J. Am. Chem. Soc. 2001, 123 (29), 6965−6972. (73) Detailed synthetic procedures and data for the identifications of a series of 9,9-dialkyl-2,7-divinyl fluorene containing chiral alkyl side chains, employed in this study, and the additional polymerization data are shown in the Supporting Information. (74) As reported previously,51 the calibration with polystyrene standards often overestimates the molecular weight averages of rigid conjugated polymers. Therefore, GPC curves versus structurally similar soluble PPP [poly(p-phenylene)] standards were recorded,51−53,56,65,66 and the Mn values of rodlike polymers measured versus polymer standards are overestimated by a factor of 1.6. For a related article on measuring Mn and Mw/Mn values by PPP standards see: Marsitzky, D.; Brand, T.; Geerts, Y.; Klapper, M.; Müllen, K. Synthesis of Rod-Coil Block Copolymers via End-Functionalized Poly(p-phenylene)s. Macromol. Rapid Commun. 1998, 19 (7), 385− 389.

(75) Additional CD and CPL spectra (in solution, aggregates, and film) under various conditions are shown in the Supporting Information. Among chiral PFVs, only 2mb does not generate CDactive aggregates due to the scarcely solubility in CHCl3. (76) Anuragudom, P.; Newaz, S. S.; Phanichphant, S.; Lee, T. R. Facile Horner−Emmons Synthesis of Defect-Free Poly(9,9-dialkylfluorenyl-2,7-vinylene). Macromolecules 2006, 39 (10), 3494−3499. (77) Liu, Q.; Liu, W.; Yao, B.; Tian, H.; Xie, Z.; Geng, Y.; Wang, F. Synthesis and Chain-Length Dependent Properties of Monodisperse Oligo(9,9-di-n-octylfluorene-2,7-vinylene)s. Macromolecules 2007, 40 (6), 1851−1857. (78) For example (aggregation-induced emission, refs 68 and 78−80): Luo, J.; Xie, Z.; Lam, J. W. Y.; Cheng, L.; Chen, H.; Qiu, C.; Kwok, H. S.; Zhan, X.; Liu, Y.; Zhu, D.; Tang, B. Z. Aggregationinduced emission of 1-methyl-1,2,3,4,5-pentaphenylsilole. Chem. Commun. 2001, 18, 1740−1741. (79) Deans, R.; Kim, J.; Machacek, M. R.; Swager, T. M. A Poly(pphenyleneethynylene) with a Highly Emissive Aggregated Phase. J. Am. Chem. Soc. 2000, 122 (35), 8565−8566. (80) Liu, J.; Su, H.; Meng, L.; Zhao, Y.; Deng, C.; Ng, J. C. Y.; Lu, P.; Faisal, M.; Lam, J. W. Y.; Huang, X.; Wu, H.; Wong, K. S.; Tang, B. Z. What makes efficient circularly polarised luminescence in the condensed phase: aggregation-induced circular dichroism and light emission. Chem. Sci. 2012, 3 (9), 2737−2747. Aggregation-induced circular dichroism (AICD) with 1,1-dimethyl-3,4-diphenylsilole containing two 2,3:5,6-di-O-isopropylidene-1-O-(4-ethynyl-benzoyl)α-D-mannofuranosyl benzoate as a substituent on 4′-substituted 1′,2′,3′-triazole in the 2,5-position. (81) We carefully checked the spectra (by the double sides coating in the symmetrical optical geometry) to avoid the unfavorable apparent chiroptical inversion artifact originate from linear dichroism induced by a mechanical stress oriented partial orientation of anisotropic specimens operating with the spin-coating. A detailed procedure is described in the experimental section (in the Supporting Information) in the following article: Guo, S.; Kamite, H.; Suzuki, N.; Wang, L.; Ohkubo, A.; Fujiki, M. Ambidextrous Chirality Transfer Capability from Cellulose Tris(phenylcarbamate) to Nonhelical Chainlike Luminophores: Achiral Solvent-Driven Helix-Helix Transition of Oligo- and Polyfluorenes Revealed by Sign Inversion of Circularly Polarized Luminescence and Circular Dichroism Spectra. Biomacromolecules 2018, 19, 449−459.

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