Annealing-Induced Circular Dichroism Enhancement in Luminescent

Article pubs.acs.org/Macromolecules

Annealing-Induced Circular Dichroism Enhancement in Luminescent Conjugated Polymers with an Intramolecular Stack Structure Young-Jae Jin,† Kyo-Un Seo,† Young-Ghil Choi,† Masahiro Teraguchi,*,‡ Toshiki Aoki,*,‡ and Giseop Kwak*,† †

Department of Polymer Science & Engineering, Polymeric Nanomaterials Laboratory, School of Applied Chemical Engineering, Kyungpook National University, 1370 Sankyuk-dong, Buk-ku, Daegu 702-701, Korea ‡ Department of Chemistry and Chemical Engineering, Graduate School of Science and Technology, and Center for Transdisciplinary Research, Niigata University, Ikarashi 2-8050, Nishi-ku, Niigata 950-2181, Japan S Supporting Information *

ABSTRACT: Two poly(diphenylacetylene) derivatives containing identical chiral pinanyl groups on the para- and metapositions of the side phenyl ring were prepared, and their circular dichroism (CD) and photoluminescence (PL) spectra were compared. The magnitudes of circular polarization (gCD) of the para- and meta-polymers were determined to be 3.1 × 10−3 and 1.4 × 10−3, respectively. The PL quantum yield (PLQY) of the para-polymer was much greater (27.8%) than that of the meta-polymer (2.61%). When the two polymers were annealed at 80 °C in toluene, their CD spectra were remarkably enhanced and reached equilibrium at gCD values of 9.6 × 10−3 and 6.0 × 10−3, respectively. The para-polymer was kinetically more favored for the CD enhancement as known from the fact that the activation energies for the reactions of paraand meta-polymers were determined to be 88 and 187 kJ mol−1, respectively. The PLQYs of both polymers were unaffected by annealing.

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INTRODUCTION Several conjugated polymers (CPs) that display circular dichroism (CD) properties have recently been developed for highly advanced applications.1−4 In particular, CPs that are either optically active or emissive are expected to exhibit circularly polarized luminescence (CPL) for their application in the field of optoelectronic device materials.5−13 Despite such attractive functions, it is still quite difficult to achieve high photoluminescence (PL) efficiency and large optical dissymmetry at the same time. This limitation arises because conventional CPs usually suffer from significant attenuation of their PL emission in solid state. This phenomenon should be attributed to the very strong intermolecular π−π interactions based on the intrinsic planar geometry of the rigid backbone. Owing to the same reason, conventional CPs cannot readily adapt to changes in asymmetry or chiral conformations either kinetically or thermodynamically. However, unlike these CPs, poly(diphenylacetylene)s (PDPAs) are quite emissive because they have a nonplanar geometry due to their highly twisted backbone.14 The PL emission of PDPAs is now believed to originate from an intramolecular excimer emission based on the intramolecular stack structure (IaSS) of the side phenyl rings.15,16 The degree of intramolecular stacking is significantly affected by the substitution position and/or the length of the alkyl side chain.17,18 Accordingly, highly emissive PDPAs can be obtained as desired by taking these concerns into consideration © XXXX American Chemical Society

in the early stages of molecular design of their monomers. Moreover, PDPAs can also be made optically active simply by introducing appropriate chiral side groups into the polymer chain.19−22 However, it is still quite difficult to predict the extent to which the polymers become optically active. In this respect, it is quite challenging to enhance the optical activity of PDPAs while still retaining the high PL efficiency. A few research groups have recently synthesized polymers having regulated π-stacked structures in their side chains.23−27 This type of chain conformation has a significant influence on the optoelectronic properties of the polymers, of which PDPAs are a representative example. In a previous study, two different PDPAs with an identical side substituent of the trimethylsilyl group on the para- and meta-positions of the side phenyl ring were synthesized by Masuda et al.28,29 Despite their nearly identical structures, the two polymers showed entirely different PL efficiency, attributed to the slight difference in the substitution position.18 The para-polymer was found to be much more emissive at shorter wavelengths than the metasubstituted polymer. In order to find a reasonable explanation for this observation, spectroscopic measurements, theoretical calculations, and direct observation of single chains using a Received: June 15, 2017 Revised: August 4, 2017

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grade cuvette with a path length of 1 mm) were also measured at 25 °C on a JASCO J-815 spectropolarimeter (with a scanning rate of 100 nm min−1, bandwidth of 1 nm, and response time of 1 s, in a single accumulation) equipped with a temperature control unit. The [α]D values were measured using a JASCO DIP-1000 polarimeter at 20 °C. The PLQYs of the polymer solutions were determined at λ = 420 nm, relative to a quinine sulfate solution in 1 N H2SO4 at room temperature, assuming a quantum yield of 0.546 when excited at λ = 365 nm. X-ray diffraction (XRD) measurements were performed at room temperature using an X-ray diffractor (PANalytical X’Pert PROMPD) in the Korea Basic Science Institute (Daegu). The samples were mounted directly into the diffractor. The experiment was carried out using Cu Kα (1.54 Å) radiation operating at 40 kV and 25 mA. The thick film samples for XRD were prepared by the solvent casting method.

high-speed atomic force microscope have been carried out. It was revealed that the different PL efficiency arises due to the difference in the degrees of stack regulation and stability of the side phenyl rings according to the substitution position. Moreover, the achiral para-polymer experienced an asymmetric rearrangement of the side phenyl rings during the annealing process in a chiral solvent owing to the variable IaSS in its solution state, leading to a quite large CD, while the metapolymer revealed no CD after the same treatment because of the highly static IaSS.30−32 Therefore, several questions arise for a system of two chiral para- and meta-substituted PDPAs. For example, does the substitution pattern also affect the CD spectra? If the chiral polymers are annealed in achiral solvent, to what extent can the CD values be altered? More importantly, how much different will the change in CD be for the two polymers with respect to kinetics? In order to answer these questions, in this study, two different chiral PDPAs containing the same chiral pinanyl group on the para- and meta-positions of the side phenyl ring were prepared (Figure 1), and their CD

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RESULTS AND DISCUSSION It is worth noting beforehand that the polymerization reaction for the production of the two chiral PDPAs was conducted very carefully at the same temperature and for the same time duration. These conditions were followed in order to exclude the possibility that the polymerization process was responsible for the differences in the CD spectra of the two polymers. It has been previously reported that the intensity of CD is quite different depending on the polymerization temperature.22 Therefore, performing the polymerization reaction under identical experimental conditions guarantees an exact comparative analysis of the annealing effect on CD of the two polymers. The two polymers studied in this work were synthesized following a previously reported method by heating the reaction mixture at 80 °C for 1 h. The para- and metapolymers had extremely high Mw of 1.3 × 106 and 1.8 × 106 g mol−1, respectively. Figure 2 shows the UV−vis, CD, and PL spectra of the two polymers in solution. As is usual in the case of chiral PDPAs,19−22 both polymers exhibited the largest CD signal at 382 nm as the first Cotton band. Other CD signals were also observed at shorter wavelengths as the second, third, and fourth Cotton bands. The first Cotton band is in accordance with the absorption band that is attributed to the resonant structure wherein the backbone and side phenyl rings intersect.32 In the previous study, we found that the maximum CD band (λmax,CD ∼ 382 nm) of chiral PDPAs does not exactly accord with the dual maximum absorption band (λmax,abs ∼ 380, 430 nm) but exactly matches the isosbestic point (∼382 nm) wherein the main chain and the side phenyl rings intersect. It was proved by polarized optical microscopy and spectroscopy using a uniaxially aligned film.32 This means that the maximum CD band originates from a certain axial chirality structure between the main chain and side phenyl rings. This is also the reason why there is little CD at the dual maximum absorption wavelengths. The magnitude of circular polarization (gCD) of the parapolymer based on its first Cotton band was 3.1 × 10−3, that is, 2.2 times larger than that of the meta-polymer (gCD = 1.4 × 10−3) (Table 1). Similarly, the optical rotation ([α]D) of the former polymer was +303° (c = 4.0 × 10−4 g mL−1 in CHCl3), which is nearly 2.2 times larger than that of the meta-polymer (+138°) in a solution of identical concentration. This indicates that the para-polymer is more favored for achieving a larger optical dissymmetry than the meta-polymer. As expected from the previous results,18 the para-polymer was much more emissive than the meta-polymer (Table 1). The PL quantum yield (PLQY) of the para-polymer was 27.8%, which is much greater than that of the meta-polymer (2.61%). The PL

Figure 1. Chemical structures of p- and m-PDPAs.

and PL properties were compared in conjunction with the annealing process. In this manner, this work aims to describe a definite guideline for the molecular design and post-treatment procedures for the development of an optically active and highly emissive PDPA derivative.

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EXPERIMENTAL SECTION

Materials. The polymers were synthesized according to a method reported in the literature.22 A stock solution of the polymer was obtained by completely dissolving it in toluene at room temperature with overnight stirring to obtain a concentration of 1.0 × 10−3 mol L−1. This solution was put into individual vials, which were capped and heated at 80 °C for different time durations and then slowly cooled down to room temperature. Subsequently, the solutions were diluted to a concentration of 5.0 × 10−4 mol L−1 using toluene, and their ultraviolet−visible (UV−vis), CD, PL, and PL excitation (PLE) spectra were measured at room temperature. In order to prepare polymer samples for the [α]D measurements, the annealed polymer was precipitated in methanol, dried under vacuum, and redissolved in CHCl3 to obtain a concentration of 4.0 × 10−4 g mL−1. Thus, the [α]D values of the polymers were measured at room temperature. The CD spectra and [α]D measurements were also obtained for the same polymers annealed at 40 and 60 °C, respectively, at different times. Chiroptical Analysis. The magnitude of the circular polarization at ground state is defined as gCD = 2 × ((εL − εR)/(εL + εR)), where εL and εR denote the extinction coefficients for left and right circularly polarized light, respectively. Experimentally, the value of gCD is determined by Δε/ε at the wavelength of the CD extremum. Measurements. The weight-average molecular weight (Mw) and the number-average molecular weight (Mn) of the polymers were determined by gel permeation chromatography (GPC) calibrated with a polystyrene standard using a JASCO liquid chromatography system consisting of PU-2080, DG-2080-53, CO-2060, UV-2070, and two polystyrene gel columns (Shodex KF-806L × 2, eluent: THF). UV−vis absorption and PL emission spectra of the solutions (SQ-grade cuvette with a path length of 10 mm) were measured on a JASCO V-650 spectrophotometer and JASCO FP-6500 spectrofluorometer, respectively, at room temperature. The CD spectra of the solutions (SQB

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polymers were excited at the λmax,CD of 382 nm instead of the λmax,abs of 380 and 430 nm, the PL intensity was still quite high. This indicates a high possibility of CPL due to optically dissymmetric structure. Although CPL spectra could not be measured at this time owing to the lack of accessibility to the instrument, the CPL spectra may give us more useful chiral information regarding the excited electronic state from which emission takes place.34 As mentioned above, it is already known that the achiral para-substituted PDPA undergoes an asymmetric change toward chiral conformation in its IaSS via the annealing process in a chiral solvent, whereas the corresponding metapolymer is completely inert to the same treatment.30−32 In order to examine the same annealing effect on the CD properties of the present chiral PDPAs, their CD and UV−vis spectra were measured by heating the polymers in toluene at 80 °C for different time durations (Figure 4). Surprisingly, the polymers exhibited a remarkable increase in the CD intensity after the annealing process, reaching equilibrium at gCD of 9.6 × 10−3 for the para-polymer and 6.0 × 10−3 for the meta-polymer after several tens of hours (inset in Figure 4 and data in Table 1). These gCD values are several times larger than those of the polymers before annealing. Simultaneously, the [α]D values of both polymers also showed a significant increase of up to +1493° and +1124°, respectively, after the same treatment. This indicates that the side phenyl rings are not arranged optimally for the optically dissymmetric, energy-minimized form just after polymerization likely owing to either steric hindrance of the side group or stiffness of the main chain. Therefore, it can be concluded that the polymers overcame a specific energy barrier for conformational transformation via the annealing process to undergo asymmetric change in the presence of the chiral side group, leading to a more definite axial chirality. Also, the UV−vis spectral profiles were subtly dependent on annealing time as shown in Figure 4. The longest wavelength bands at 430 nm due to the π−π transition of main chain tended to progressively red-shift with annealing time. In correspondence to the UV−vis spectral changes, the PLE spectra showed relatively increased peak intensity at the long wavelength after the annealing, indicating the relatively increased contribution of main chain to the PL emission (Figure S1). In order to understand the annealing-induced CD enhancement with respect to the kinetics of the process, CD spectra were measured with the polymers annealed in toluene at different temperatures. As shown in Figure 5, the rate of CD enhancement was found to be highly dependent on the annealing temperature. The increasing rate of gCD value was greater in the polymer solution that was annealed at a higher temperature. The reaction rate constants (k) were determined from eq 1 via regression analysis (Table 1). Using these values,

Figure 2. (a) CD/UV−vis and (b) PL emission spectra (excited at 420 nm) of p- and m-PDPA solutions (c = 5.0 × 10−4 mol L−1 in toluene). Inset: corrected PL emission spectra in consideration of overlapping between the UV−vis absorption and PL emission bands.

emission bands seemed to slightly overlap with the UV−vis absorption band, more especially for the meta-polymer. Therefore, we evaluated a correction for PL emission spectra according to a method reported in the literature.33 The corrected (“true”) PL emission spectra are shown in the inset of Figure 2b. In comparison with the observed spectra, the corrected PL spectra showed a slightly larger band area in a shorter wavelength range of less than 500 nm, indicating a selfquenching due to the reabsorbance. In order to check any relation between PL and CD, we also measured both excitation wavelength-variable PL emission and PL excitation (PLE) spectra of the two polymers (Figure 3). The shape of PL spectra was constant regardless of the excitation wavelengths while only the PL intensity differed slightly. PLE spectra were also independent of the PL monitoring wavelengths, indicating the existence of single excited species. Indeed, even when the

Table 1. Chiroptical Properties, Kinetic Parameters, and PLQYs of p- and m-PDPAs kinetic parameters k

chiroptical properties polymer

gCD × 10−3

[α]D

p-PDPA m-PDPA

3.1 (9.6)f 1.4 (6.0)f

303 (1493)f 138 (1124)f

a

b

c

PL emissiona

40 °C

60 °C

80 °C

7.0 × 10−3 3.0 × 10−5

8.6 × 10−2 2.5 × 10−2

3.1 × 10−1 9.6 × 10−2

Ead

(kJ mol−1) 88 187

PLQYe (%) 27.8 (25.8)f 2.61 (2.25)f

5.0 × 10−4 mol L−1 in toluene. b4.0 × 10−4 g mL−1 in CHCl3. cReaction rate constant for the annealing-induced CD enhancement. dActivation energy for the annealing-induced CD enhancement. eMeasured at 420 nm and determined using the reference point method as described in the Experimental Section. fValues at CD enhancing equilibrium after the annealing process. a

C

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Figure 3. (a, b) PL and (c, d) PLE spectra of (a, c) p-PDPA and (b, d) m-PDPA in toluene solution (c = 5.0 × 10−4 mol L−1 in toluene).

Figure 5. CD enhancement of (a) p-PDPA and (b) m-PDPA solutions (c = 5.0 × 10−4 mol L−1 in toluene) according to the annealing time at different temperatures of 40, 60, and 80 °C. Figure 4. CD and UV−vis spectra of (a) p-PDPA and (b) m-PDPA solutions (c = 5.0 × 10−4 mol L−1 in toluene) during the annealing process at 80 °C (inset: plot of gCD according to the annealing time).

the activation energy of the reaction (Ea) was calculated by applying the Arrhenius equation (eq 2). D

DOI: 10.1021/acs.macromol.7b01283 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules gCD = gCD,max (1 − e−tk )

substituted polymer was more optically active and emissive than the meta-polymer, when analyzed after the polymerization. When these polymers were annealed at appropriate temperatures in toluene, their CD was significantly enhanced. The annealing process was monitored by the change in gCD, and it was found that the polymers underwent an asymmetric conformational change in their IaSS via the post-treatment process, leading to a more definite axial chirality. The Ea value was much lower for the para-polymer in comparison with the meta-polymer, indicating that the former undergoes a conformational change more efficiently than the latter. The PLQYs of both polymers were almost unaffected by the annealing treatment. Thus, the goal of enhancing the CD significantly while maintaining the PL efficiency was achieved simply by annealing the chiral polymers in an achiral solvent. It is expected that the molecular design and post-treatment method discussed in this work will be helpful for the development of highly advanced optoelectronic materials.

(1)

where gCD,max is the value of gCD at equilibrium and t refers to the annealing time duration.

k = Ae−Ea / RT

(2)

where k, A, R, and T refer to the rate constant, frequency factor, gas constant, and absolute temperature, respectively. Thus, Ea was determined to be 88 kJ mol−1 for the parapolymer, which was almost half that for the meta-polymer (187 kJ mol−1) (Table 1). This suggests that the para-substituent lowers the energy barrier for the conformational transformation more efficiently than the meta-substituent. In other words, the polymer having the side group in the para-position is kinetically more favored for the asymmetric rearrangement in IaSS. Similar to previously studied PDPA derivative,19 the present polymers showed no significant decrease in PLQYs during the annealing process. The PLQYs of para- and meta-polymers were 25.8 and 2.25%, respectively, after the annealing treatment (Table 1). The PLQYs were found to decrease by a mere 2.0 and 0.36% from its values before the annealing process. This observation suggests that while the annealing treatment influences CD in a significant manner, it has little or no influence on the PL of the polymers. The explanation for this result is that the conformational change toward a larger optical dissymmetry occurs via the annealing process, but the degree of stacking of the side phenyl rings is not affected by the asymmetric conformational change. In addition, the conformational change was reflected on their morphologies in bulk films. Figure 6 shows the XRD patterns of the two polymers before

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.7b01283. PLE spectra of PDPAs after annealing (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: (M.T.) [email protected]. *E-mail: (T.A.) [email protected]. *E-mail: (G.K.) [email protected]. ORCID

Young-Jae Jin: 0000-0002-4670-4199 Toshiki Aoki: 0000-0002-2536-7373 Giseop Kwak: 0000-0003-3111-0918 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) grants funded by the Korean government (MEST) (2014R1A2A1A11052446). We thank Prof. Jong-Keun Son (Yeungnam University) for use of a polarimeter.

Figure 6. XRD patterns of PDPAs before and after annealing at 80 °C for 48 h.

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and after the annealing process. The small-angle peak at around 6° due to an intermolecular packing structure shifted slightly to a larger angle after the annealing, indicating the interchain distance became shorter. On the other hand, the broad halo signals at around 25° indicate that both polymers are basically amorphous. The peak intensity ratio of I6°/I25° was increased slightly after the annealing, indicating the regularly packed chains became a little more.

REFERENCES

(1) 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, 13752−13990. (2) Watanabe, K.; Akagi, K. Helically Assembled π-Conjugated Polymers with Circularly Polarized Luminescence. Sci. Technol. Adv. Mater. 2014, 15, 044203−044223. (3) Yashima, E. Synthesis and Structure Determination of Helical Polymers. Polym. J. 2010, 42, 3−16. (4) Yashima, E.; Maeda, K.; Iida, H.; Furusho, Y.; Nagai, K. Helical Polymers: Synthesis, Structures, and Functions. Chem. Rev. 2009, 109, 6102−6211. (5) Yang, Y.; Correa da Costa, R.; Smilgies, D.-M.; Campbell, A. J.; Fuchter, M. J. Induction of Circularly Polarized Electroluminescence from an Achiral Light-Emitting Polymer via a Chiral Small-Molecule Dopant. Adv. Mater. 2013, 25, 2624−2628.

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CONCLUSIONS A method to enhance the optical activity of luminescent, chiral CPs with IaSS has been examined in this work. Two chiral PDPAs which contain the same chiral pinanyl group on the para- and meta- positions of the side phenyl ring were prepared, and their chiroptical properties were compared. The paraE

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(23) Nakano, T. Synthesis, Structure and Function of π-Stacked Polymers. Polym. J. 2010, 42, 103−123. (24) Rathore, R.; Chebny, V. J.; Kopatz, E. J.; Guzei, L. A. RedoxInduced Transformation from an Extended to a π-Stacked Conformer in Acyclic Bis(catecholacetal)s of Acetylacetone. Angew. Chem., Int. Ed. 2005, 44, 2771−2774. (25) Rathore, R.; Abdelwahed, S. H.; Guzei, L. A. Synthesis, Structure, and Evaluation of the Effect of Multiple Stacking on the Electron-Donor Properties of π-Stacked Polyfluorenes. J. Am. Chem. Soc. 2003, 125, 8712−8713. (26) Nakano, T.; Yade, T. Synthesis, Structure, and Photophysical and Electrochemical Properties of a π-Stacked Polymer. J. Am. Chem. Soc. 2003, 125, 15474−15484. (27) Nakano, T.; Takewaki, K.; Yade, T.; Okamoto, Y. Dibenzofulvene, a 1,1-Diphenylethylene Analogue, Gives a π-Stacked Polymer by Anionic, Free-Radical, and Cationic Catalysts. J. Am. Chem. Soc. 2001, 123, 9182−9183. (28) Tsuchihara, K.; Masuda, T.; Higashimura, T. Polymerization of Silicon-Containing Diphenylacetylenes and High Gas Permeability of the Product Polymers. Macromolecules 1992, 25, 5816−5820. (29) Tsuchihara, K.; Masuda, T.; Higashimura, T. Tractable SiliconContaining Poly(diphenylacetylenes): Their Synthesis and High Gas Permeability. J. Am. Chem. Soc. 1991, 113, 8548−8549. (30) Kim, H.; Jin, Y.-J.; Kim, B. S.-I.; Aoki, T.; Kwak, G. Optically Active Conjugated Polymer Nanoparticles from Chiral Solvent Annealing and Nanoprecipitation. Macromolecules 2015, 48, 4754− 4757. (31) Kim, H.; Lee, D.; Lee, S.; Suzuki, N.; Fujiki, M.; Lee, C.-L.; Kwak, G. Optically Active Conjugated Polymer from Solvent Chirality Transfer Polymerization in Monoterpenes. Macromol. Rapid Commun. 2013, 34, 1471−1479. (32) Lee, D.; Jin, Y.-J.; Kim, H.; Suzuki, N.; Fujiki, M.; Sakaguchi, T.; Kim, S. K.; Lee, W.-E.; Kwak, G. Solvent-to-Polymer Chirality Transfer in Intramolecular Stack Structure. Macromolecules 2012, 45, 5379− 5386. (33) Castiglioni, E.; Abbate, S.; Lebon, F.; Longhi, G. Ultraviolet, Circular Dichroism, Fluorescence, and Circularly Polarized Luminescence Spectra of Regioregular Poly-[3-((S)-2-Methylbutyl)-Thiophene] in Solution. Chirality 2012, 24, 725−730. (34) Longhi, G.; Castiglioni, E.; Koshoubu, J.; Mazzeo, G.; Abbate, S. Circularly polarized luminescence: a review of experimental and theoretical aspects. Chirality 2016, 28, 696−707.

(6) Watanabe, K.; Iida, H.; Akagi, K. Circularly Polarized Blue Luminescent Spherulites Consisting of Hierarchically Assembled Ionic Conjugated Polymers with a Helically π-Stacked Structure. Adv. Mater. 2012, 24, 6451−6456. (7) Grell, M.; Oda, M.; Whitehead, K. S.; Asimakis, A.; Neher, D.; Bradley, D. D. C. A Compact Device for the Efficient, Electrically Driven Generation of Highly Circularly Polarized Light. Adv. Mater. 2001, 13, 577−580. (8) Oda, M.; Nothofer, H.-G.; Lieser, G.; Scherf, U.; Meskers, S. C. J.; Neher, D. Circularly Polarized Electroluminescence from LiquidCrystalline Chiral Polyfluorenes. Adv. Mater. 2000, 12, 362−365. (9) Meskers, S. C. J.; Peeters, E.; Langeveld-Voss, B. M. W.; Janssen, R. A. Circular Polarization of the Fluorescence from Films of Poly(pphenylene vinylene) and Polythiophene with Chiral Side Chains. Adv. Mater. 2000, 12, 589−594. (10) Grell, M.; Bradley, D. D. C. Polarized Luminescence from Oriented Molecular Materials. Adv. Mater. 1999, 11, 895−905. (11) Montali, A.; Bastiaansen, C.; Smith, P.; Weder, C. Polarizing Energy Transfer in Photoluminescent Materials for Display Applications. Nature 1998, 392, 261−264. (12) Peeters, E.; Christiaans, M. P. T.; Janssen, R. A. J.; Schoo, H. F. M.; Dekkers, H. P. J. M.; Meijer, E. W. Circularly Polarized Electroluminescence from a Polymer Light-Emitting Diode. J. Am. Chem. Soc. 1997, 119, 9909−9910. (13) Langeveld-Voss, B. M. W.; Janssen, R. A. J.; Christiaans, M. P. T.; Meskers, S. C. J.; Dekkers, H. P. J. M.; Meijer, E. W. Circular Dichroism and Circular Polarization of Photoluminescence of Highly Ordered Poly{3,4-di[(S)-2-methylbutoxy]thiophene}. J. Am. Chem. Soc. 1996, 118, 4908−4909. (14) Jin, Y.-J.; Kwak, G. Properties, Functions, Chemical Transformation, Nano-, and Hybrid Materials of Poly(diphenylacetylene)s toward Sensor and Actuator Applications. Polym. Rev. 2017, 57, 175− 199. (15) Lee, W.-E.; Kim, J.-W.; Oh, C.-J.; Sakaguchi, T.; Fujiki, M.; Kwak, G. Correlation of Intramolecular Excimer Emission with Lamellar Layer Distance in Liquid-Crystalline Polymers: Verification by the Film-Swelling Method. Angew. Chem., Int. Ed. 2010, 49, 1406− 1409. (16) Kwak, G.; Minakuchi, M.; Sakaguchi, T.; Masuda, T.; Fujiki, M. Alkyl Side-Chain Length Effects on Fluorescence Dynamics, Lamellar Layer Structures, and Optical Anisotropy of Poly(diphenylacetylene) Derivatives. Macromolecules 2008, 41, 2743−2746. (17) Jin, Y.-J.; Bae, J.-E.; Cho, K.-S.; Lee, W.-E.; Hwang, D.-Y.; Kwak, G. Room Temperature Fluorescent Conjugated Polymer Gums. Adv. Funct. Mater. 2014, 24, 1928−1937. (18) Lee, W.-E; Oh, C.-J.; Park, G.-T.; Kim, J.-W.; Choi, H.-J.; Sakaguchi, T.; Fujiki, M.; Nakao, A.; Shinohara, K.; Kwak, G. Substitution Position Effect on Photoluminescence Emission and Chain Conformation of Poly(diphenylacetylene) Derivatives. Chem. Commun. 2010, 46, 6491−6493. (19) Kim, H.; Seo, K.-U.; Jin, Y.-J.; Lee, C.-L.; Teraguchi, M.; Kaneko, T.; Aoki, T.; Kwak, G. Highly Emissive, Optically Active Poly(diphenylacetylene) Having a Bulky Chiral Side Group. ACS Macro Lett. 2016, 5, 622−625. (20) Lee, D.; Kim, H.; Suzuki, N.; Fujiki, M.; Lee, C.-L.; Lee, W.-E.; Kwak, G. Optically Active, Lyotropic Liquid Crystalline Poly(diphenylacetylene) Derivative: Hierarchical Chiral Ordering from Isotropic Solution to Anisotropic Solid Films. Chem. Commun. 2012, 48, 9275−9277. (21) Jim, C. K. W.; Lam, J. W. Y.; Leung, C. W. T.; Qin, A.; Mahtab, F.; Tang, B. Z. Helical and Luminescent Disubstituted Polyacetylenes: Synthesis, Helicity, and Light Emission of Poly(diphenylacetylene)s Bearing Chiral Menthyl Pendant Groups. Macromolecules 2011, 44, 2427−2437. (22) Aoki, T.; Kobayashi, Y.; Kaneko, T.; Oikawa, E.; Yamamura, Y.; Fujita, Y.; Teraguchi, M.; Nomura, R.; Masuda, T. Synthesis and Properties of Polymers from Disubstituted Acetylenes with Chiral Pinanyl Groups. Macromolecules 1999, 32, 79−85. F

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