Circularly Polarized Luminescence in Chiral Molecules and

Perspective pubs.acs.org/JPCL

Circularly Polarized Luminescence in Chiral Molecules and Supramolecular Assemblies Jatish Kumar, Takuya Nakashima,* and Tsuyoshi Kawai*

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on August 23, 2015 | http://pubs.acs.org Publication Date (Web): August 18, 2015 | doi: 10.1021/acs.jpclett.5b01452

Graduate School of Materials Science, Nara Institute of Science and Technology, NAIST, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan ABSTRACT: Circularly polarized luminescence, or CPL, is a luminescence phenomenon that provides the differential emission intensity of right and left circularly polarized light, thereby providing information on the excited state properties of the chiral molecular systems. In recent years, there has been a growing interest toward the development of organic chromophores capable of circularly polarized emission due to their potential applications in sensors, asymmetric synthesis as well as display and optical storage devices. The major drawback with organic molecules is the low dissymmetric factors exhibited by these systems. One of the recent strategies adopted for the improvement in luminescence dissymmetry of organic systems is through the controlled self-assembly of chromophores. In this Perspective, we highlight the recent experimental and theoretical developments in the field of chiral organic chromophoric systems and their self-assembly, that has produced promising results toward the enhancement of glum values in CPL.

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values are obtained for magnetic dipole-allowed and electric dipole-forbidden transitions. Due to the favorable transitions possible, lanthanide complexes often show high glum values.12 Among various chiral luminescent molecular systems investigated, Eu(III) complexes exhibit high glum values, with ∼1.3 being the highest reported until date in cesium tetrakis(3heptafluoro-butylryl-(+)-camphorato) Eu(III) complexes.13 In contrast to inorganic complexes, the advantage with organic molecules is that their emission can be readily tuned by bringing about modulations in their excited state electronic levels. The modulations in the electronic states have been achieved by processes such as self-assembly, by chemical transformations of the substituents, and by changing the environment through external stimuli.14,15 In spite of these advantages, organic systems are not the best candidates used in CPL studies due to the relatively low glum values exhibited by these systems. Recently, attempts are being made by different research groups to synthesize organic systems that possess high g lum . Herein, we highlight the recent theoretical and experimental developments in the field of chiral organic chromophoric systems and their self-assembly, that has produced promising results toward the enhancement of glum in CPL. We also try to analyze the future prospects of this field, which would help researchers design molecular systems that can be utilized effectively for the fabrication of CPL active materials. For detailed mathematical derivations as well as the instrumentation set up, readers may be referred to the extensive reviews published on CPL.6−9 First we analyze the CPL properties of organic molecules in the monomeric state.8 Some of the π-conjugated systems

ature has produced a large number of macroscopic objects, ranging from sea shells to the human DNA, that possess chiral morphologies. Transfer of chiral information on biomolecular components has facilitated the formation of macroscopic chiral shapes in living organisms.1 Various techniques are being developed in the laboratory to mimic the complex nature of chirality transfer in these systems.2,3 Chirality in molecular systems and assemblies is a state that is derived from the dissymmetry of the environment, and the fascinating chiroptical properties exhibited by such systems is still an active area of research.4 Circular dichroism (CD), which measures the difference in absorption between the left- and right-handed circularly polarized light, has been extensively used for the investigation of such properties.5 Hence, CD provides information on the ground state chiroptical properties of molecules. On the other hand, the differential emission of right and left circularly polarized light can be measured using a relatively new technique known as the circularly polarized luminescence (CPL), which is correlated with the excited state properties of the chiral systems.6−9 Hence, the CPL signatures can be used as a powerful tool for obtaining the stereochemical, conformational, and three-dimensional structural information on chiral molecules and materials in the excited state. The extent of chiral dissymmetry in fluorescence is quantified using the anisotropy factor, glum, of CPL, which is given by the equation glum = 2(IL − IR)/(IL + IR), where IL and IR are the intensities of the left- and right-handed circularly polarized emissions, respectively.6−11 The maximum possible value of glum is 2 in magnitude and the values are within the range of −2 to +2. Theoretically, glum is simply approximated by 4|m|cos θ/|μ|, where |m| and |μ| are the magnitudes of magnetic and electric transition dipole moment vectors, respectively, and θ is the angle between these vectors.6−9 Usually high anisotropic factor © XXXX American Chemical Society

Received: July 9, 2015 Accepted: August 13, 2015

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DOI: 10.1021/acs.jpclett.5b01452 J. Phys. Chem. Lett. 2015, 6, 3445−3452

The Journal of Physical Chemistry Letters

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analogous to a one-handed helix. Intense CPL with relatively large dissymmetry factors (10−3) was exhibited by the oligomers due to the planar chirality of the paracyclophane skeleton in the excited state (Figure 1c). In another report, a conformationally stable macrocycle possessing chiral propeller-shaped structure was synthesized, which gave rise to an emitting species with intense CPL and a large anisotropic factor of 1.1 × 10−2.26 In this case, the gabs and glum values showed small differences indicating only minute conformational changes between the ground and the excited states due to complete fixation by the [2.2]paracyclophane bridge methylenes. Further, a vast variety of molecules exhibiting CPL activity has been investigated, but the detailed discussion of these systems are out of the scope of this article. The CPL studies on small, nonpolymeric, and nonaggregated organic molecules were summarized in a recent review by de la Moya and co-workers.8 In that article, the authors explain the design strategy for CPL systems with enhanced fluorescence quantum yields, but the low glum value (3 × 10−2 being the highest value reported) remained the limiting factor for simple organic chiral molecules. In contrast, we focus on the approaches adopted by researchers for effectively enhancing the luminescence dissymmetry in chiral organic molecules. One of the important areas where CPL could be effectively used is to study the excited state properties in the case of excimers. An excimer or excited dimer is formed when a ground state molecule interacts with another molecule in the excited state to form a short-lived dimer. Brittain and Fendler were the first in 1980 to investigate the CPL from the excimeric state of enantiomers of pyrene derivatives.27 At low concentration, no CPL was observed, ruling out the CPL from the singlet excited state. With increasing concentration, CPL effect was observed which was found to be proportional to the extent of excimer formation. An absolute screw sense of the excimer configuration of pyrenes could be assigned from the sign of the CPL


High luminescence dissymmetry is obtained for magnetic dipoleallowed and electric dipole-suppressed transitions; unfavorable transitions in organic systems make the enhancement of glum a challenging task. wherein CPL of molecules dispersed in solution has been widely investigated include helicenes,16−19 chiral bichromophores,20−23 twisted polycyclics,24 and chiral cyclophanes.25,26 Among them, helicenes have long attracted much attention due to their π-conjugated helical structures emitting CPL. Significantly large CPL (glum ∼ − 0.030) was observed for [7]helicenes containing the fluorene or spirofluorene.17 CPL was studied from axially chiral bichromophoric systems, in which two fluorophores are arranged in a chiral fashion.20−23 Chiral effects in fluorescence in such systems are attributed to the intramolecular exciton coupling interactions between fluorophores,5 and the glum values were in the range of 0.1−0.5%.20−23 A combination of CD and CPL was used to investigate the conformational changes of chiral through space conjugated oligomers with planar-chiral [2.2]paracyclophane junctions in the ground and excited state (Figure 1a).25 Similarities in the chiroptical properties of the cyclophane derivatives observed in the ground state (constant gabs values) were attributed to the equivalent orientations of the electric transition moments of the two adjacent interacting chromophores (Figure 1b). In contrast, the chiroptical properties were found to be gradually enhanced in the excited state (glum values) with the increase in the number of stacked π-electron systems, which points to the fact that photoexcitation resulted in the folding of the oligomers into a form that is

Figure 1. (a) Molecular structure of (Sp)-2, 3 and 4 (R = n-C12H25). (b) gabs and (c) glum plots of (Sp)-2−4, and (Rp)-2−4 in chloroform (1.0 × 10−5 M). Reprinted with permission from ref 25 (Copyright 2014 Wiley-VCH). 3446




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Figure 3. (a) AFM image, (b) glum spectra of self-assembled fibers, and (c) schematic representation of the self-assembly and enhanced CPL of Cy-PBIs.

Figure 2. (a) Structure of a bichromophoric cyclohexane molecule bearing PBIs (Cy-PBI) and (b) the CPL spectrum of the molecule in chloroform (1 × 10−5 M). (c) Schematic illustration of excimer formation of [4]rotaxane in γ-CD that gives excimer CPL in a small amount of ammonia-containing H2O. Reprinted with permission from ref 29 and 31 (Copyright 2013 and 2014 Wiley-VCH).

first demonstrated that the self-assembled structures resulted in more than an order of magnitude higher CPL dissymmetry factors when compared with monomeric state of the molecule.29 Cy-PBIs (Figure 2a) self-assembled into helical fibers in methylcyclohexane (MCH), which gave a glum value of 2 × 10−2 dramatically enhanced relative to a value of 6 × 10−4 observed for the monomers dispersed in chloroform (Figure 3a-c). We then reported that the morphology of the aggregates plays a crucial role in deciding the luminescence dissymmetry.36 The one-dimensional fibrous aggregates of binaph-PBIs in MCH displayed twice the value relative to the spherical aggregates formed in chloroform37 at higher concentration (glum = 8 × 10−3) (Figure 4b−d). Moreover, the dissymmetry of the luminescence in the fibrous aggregates could be modulated depending on the length of the nanofibers which in turn could be successfully tuned by varying the enantiomeric excess; the longer the fibers, higher was the anisotropic factor (Figure 4e, f).38 In a similar but slightly different approach, CPL was observed from helical assemblies of tris(phenylisoxazolyl)benzene derivative possessing a PBI moiety.39 No CPL could be observed in the monomers whereas the assemblies exhibited positive Cotton effect with a positive glum value of 0.007. It is expected that the transition dipole moments are suppressed in the π-stacked state, which could be the reason for their quenched emission and enhanced glum values. These experiments point to the fact that chiral helical assemblies can act as efficient source of circularly polarized light. Self-assemblies of heterocyclic helicenes exhibited a luminescence dissymmetry ratio of 0.01.40 However, it was noted that an increased ordering of the aggregates also resulted in a large degree of linear polarization (P = 0.39) which can greatly affect the CPL measurement. Hence, during CPL measurements, especially for aggregated systems and solid samples, precautions must be taken to ensure the complete removal of linearly polarized emission in the direction of emission detection.7,8,39,41 In contrast to lanthanide complexes, wherein long lifetimes allows any photoselected orientational distribution to randomize in the time scale between excitation and emission, short lifetimes in organic samples make them more prone to such artifacts. CPL microscopic investigations

signal.28 Negative signal indicated an excimer configuration with a right-handed screw sense. The wavelength dependence of glum-values was assigned to the presence of several kinds of excimer configurations. Excimer-like CPL was also observed in bichromophoric systems of perylene bisimide (PBI) possessing cyclohexane as the chiral central core unit (Cy-PBI, Figure 2a).29 Both monomeric and excimer-like emission could be observed in the same CPL spectrum. The emission from the locally excited state was observed at a wavelength of 540 nm with a low glum value (6 × 10−4), whereas emission from excimer-like state was observed at 630 nm with a higher glum value of 8 × 10−3 with an inversion of sign relative to that of monomeric emission (Figure 2b). CPL was also observed from spatially restricted excimer of pyrene molecules within the γCD cavity.30,31 The strong CPL signal (glum = −1.5 × 10−2) is believed to arise from the two stacked pyrenes existing in the rotaxane in an asymmetrically twisted manner (Figure 2c). From the above discussions it is clear that creation of excimer is a suitable method to enhance the glum in organic molecular systems. The major challenge faced by researchers in the field of CPL is to enhance the anisotropic factor in luminescence. Different approaches have been adopted in this direction to improve the luminescence dissymmetry in organic molecular systems. These approaches include methods such as the formation of receptorion complexes,32 configurational changes upon binding with guest ions or molecules33−35 and the self-assembly of molecules to form chiral aggregated structures.36−46 A comprehensive analysis on the anion responsive CPL investigations was done by Maeda, in which he provides details on the anion-driven chirality induction and the changes in excited state properties therein of various π-conjugated molecules.34 We herein focus our discussion on a more important methodology that has been adopted widely for the enhancement of glum in organic systems, which is through the self-assembly of molecules. π-Conjugated dye systems have been extensively studied in this regard due to the controlled self-assembly possible in such systems.14,15 We 3447




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Figure 4. (a) Chemical structure of binaph-PBIs [R = CH-(C6H13)2]. TEM images of (b) spherical and (c) fibrous assemblies of (R)-binaph-PBI in chloroform and MCH, respectively. (d) Plots of glum as a function of concentration for R (solid lines) and S (broken lines) isomers of the molecule in chloroform (red traces) and MCH (blue traces).36 (e) SEM images and (f) CPL spectra of the coassembly of (R)- and (S)-binaph-PBIs at varying ee values in MCH. Reprinted with permission from ref 38 (Copyright 2015 Wiley-VCH).

Figure 5. Mechanism for the fibrous aggregate formation from the trimeric disk of (M)-helicene and CD and CPL spectra of the aggregates (0.40 mM) in chloroform. Reprinted with permission from ref 43 (Copyright 2011 Wiley-VCH).

on individual aggregate microstructures of a copolymer film exhibited broad distribution of CPL dissymmetry ranging from positive to negative glum values for the same isomer.42 The authors attributed this large distribution of the glum values to an optical effect arising from phase retardation along the optical path of CPL inside the sample. A phthalhydrazide-functionalized helicene forms trimeric disks through hydrogen bonding in nonpolar solvents such as toluene and chloroform, which in turn stack to screw-shaped fibrous assemblies with respect to time (Figure 5).43 The assemblies of M and P isomers exhibited mirror image CPL spectra with the glum of 0.035 at the peak maxima. Supramolecular gels formed from an achiral C3symmetric molecule produced CPL with a glum of 0.80 × 10−3 at most, where spontaneous symmetry breaking was considered to take place during the self-assembly into fibers with the chiral twists and the sign of glum being positive and negative by chance.44 The mechanical stirring and the additive of chiral molecules further enhanced the |glum| values up to 1.2 × 10−2 and 2.3 × 10−3, respectively. In another report on CPL from self-assembled aggregates, UV light was used as source of external stumuli to achieve the photoswitching of CPL in supramolecular assemblies comprising of azobenzene-linked phenylene ethynylene derivatives.45 As discussed earlier, self-assembly leads to enhancement of glum values. However, the major drawback with this approach is the significant fluorescence quenching associated with aggregation, which restricts the use of these systems as efficient

CPL active materials. Interestingly, this hurdle could be overcome by the combined effect of aggregation-induced emission (AIE) and CPL in silole derivatives possessing chiral sugar moieties (Figure 6).46 Although no CD or fluorescence emission was observed in the solution state, the aggregation of the molecule enhanced the CD and fluorescence signals. The fluorescence quantum yield increased by 136-fold in the solid state due to the AIE effects. CPL signals with surprisingly large glum values (0.08−0.32) corresponding to right-handed helical nanoribbons and superhelical ropes were observed for the assemblies under different experimental conditions (Figure 6). Similar effect of AIE and CPL was later observed in selfassembled helical nanofibers of leucine47 and valine 48 containing luminogens.

Helical aggregates formed through the self-assembly of chiral molecules can function as efficient source of circularly polarized light. Theoretical investigations have also been carried out on the molecular aggregates to understand the role of molecular packing on the luminescence dissymmetry in CPL. It was Spano’s group which extensively used various theoretical models to investigate the degree of circular polarization of 3448




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Figure 6. CPL (left) and gem (right) spectra of AIE lumonophore (chemical structure is shown) in various states together with fluorescence microscope image under UV excitation prepared by natural evaporation of DCE solution. Reprinted with permission from ref 46 (Copyright 2012 Royal Society of Chemistry).

Theoretically, CPL dissymmetry depends on a modulated sum over the excitonic couplings between the interacting chromophoric units in case of aggregated structures. luminescence from one-dimensional, helical aggregates of chromophoric molecules, namely chiral oligophenylenevinylene (MOPV, Figure 7). Initially, the coupling between the electronic excitation and a local intramolecular vibrational mode was studied. It was observed that the glum for the 0−0 vibronic band depends solely on the number of coherently coupled molecules and is independent of the relative strength of electronic coupling between chromophores and excitationvibration coupling.49 In contrast, glum was found to decrease with decreasing strength of the electronic coupling for the higher vibronic transitions. Hence, it can be concluded that for the strong electronic coupling, glum is almost constant throughout the vibronic transitions whereas for the weak coupling the disymmetry turns out to be very small for all vibronic transitions except for the 0−0 transition. In contrast to the PL spectrum, glum is extremely sensitive to long-range intermolecular interactions and it was proved in another report by the same group that truncating the excitonic coupling beyond the sixth nearest neighbor results in a 30% increase in glum even though the PL spectrum remains unchanged.50 Later, disordered helical aggregates were studied in which CPL was used to probe the exciton coherence in such systems.51 In the strong disorder limit where the exciton is localized on a single chromophore, glum at 0−0 was found to be zero. With decreasing disorder and expanding coherence function, glum at

Figure 7. (a) Assembly of left-handed MOPV chiral aggregate through H-bonded dimer intermediates. (b) Calculated CPL dissymmetry line strengths as a function of the truncation of the couplings. Reprinted from ref 52. 3449



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nanoribbons.65 The robustness and excellent optical properties of these semiconductor nanomaterials could make them a promising candidate of CPL source in combination with selfassembly and plasmonic NPs.67

0−0 transition increases more rapidly than the sideband dissymmetries, resulting in a pronounced effect near the 0−0 transition frequency. Later, the authors investigated the extreme sensitivity of CPL to long-range excitonic interactions inside a helical aggregate.52 The CPL dissymmetry, was found to depend on a modulated sum over the excitonic couplings

Chiral nanoparticles and their assemblies are possible candidates for CPL source, which could be further enhanced with plasmonic nanoparticles.


glum ∝Σn,sJn,n + s s sin(ϕs)

where Jn,n+s is the coupling between molecules separated by s lattice spacing, and φ is the pitch angle between adjacent chromophores. The equation reveals the dependence of glum on extended couplings, and hence its ability to sense long-range interactions. In terms of practical applications out of CPL active materials, light emitting polymers and liquid crystalline materials with chiral substituents offer promise.53−60 Pure CPL was obtained from films of glass-forming chiral nematic liquid crystals in which light-emitting dopants are embedded.53 This chiral nematic host material induced the selective reflection of circularly polarized light. The alignment of the luminophores was in such a way that it produced almost pure circular polarization within the wavelength band of the emitted light. CPL 53−57 and circularly polarized electroluminescence (CPEL)58 were observed from the films of π-conjugated polymers tethering chiral side-alkyl chains such as polyfluorenes,54 poly(phenylene ethynylene),55 thiophene-based copolymers,56 and poly(p-phenylenevinylene).57,58 Some of them showed very high glum values over 0.154−56 due to the macroscopic chiral helical stacking of π-conjugated units, which may enhance the circular polarization of emitting photon in a similar manner to the external effect by cholesteric liquid crystals.53 Inherent helical polymers also exhibited CPL from chiral coaggregated states with small chiral molecules59 or purely single-handed helical state in solution induced by the effect of chiral side alkyl chains.60 Light induced switching of CPL was achieved in films comprising of dithienylethene linked fluorescent π-conjugated aromatic units.61 A combination of experimental and theoretical expertise can help in improving the luminescence dissymmetry in case of chiral organic molecules. When individual chromophores come close together, their dipoles couple, and the strength of this coupling is largely dependent on the distance and angle between the interacting units. It is observed that the optical and electronic excitation of materials containing uniaxially arranged luminophores produce linearly polarized emission whereas CPL is obtained from molecules arranged in a helical fashion. The former has already been achieved and is therefore more technologically advanced. The latter being an excited state chiral property is more challenging; however this can be accomplished by designing molecular systems considering their geometries, self-assembling behavior, and optical and electronic properties. Recently, CPL has been demonstrated in semiconductor nanoparticles (NPs)62,63 as well as plasmonic NPs.64 These examples include the ligand induced CPL from CdSe NPs62 and CPL from CdS NPs synthesized inside protein cages.63 The enhanced electromagnetic field induced by localized surface plasmon resonance (LSPR) led to emphasized CPL in assemblies of porphyrin derivatives on silver NPs.64 Moreover, recent reports suggested intrinsic chiral geometries for truncated tetrahedral CdTe NPs,65 and CdSe/ZnS core/ shell NPs and nanorods.66 Circularly polarized light was utilized for inducing chirality in CdTe NPs and helically twisted

The examples presented in this Perspective are clear illustration of the fact that (i) precise molecular design, (ii) integration into higher order structures and (ii) the control over the self-assembly to form nanostructures possessing desired spectral features can pave the way for the fabrication of efficient CPL active materials. Even though, the glum values attained are quite low, the higher luminescence quantum yield and the tunability in emission make the organic systems superior to their inorganic counterparts in terms of practical applications. Moreover, controlled self-assembly allows the modulation of the glum values which is a critical factor in device applications. With the advent of CPL microscopes, the technique is gaining vast importance. CPL active materials have the potential to replace the currently used inks in anticounterfeiting technology to provide additional levels of security. These systems can function as smart materials in spectroscopic and 3D displays. They have also been explored to be used in a wide variety of applications including data storage and processing, as CPL sensors and biological probes. The results on CPL of organic systems are promising and focused research in this direction can lead to the development of CPL active systems that can function as the materials for future technology.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (T.N.). *E-mail: [email protected] (T.K.). Notes

The authors declare no competing financial interest. Biographies Jatish Kumar is a JSPS postdoctoral researcher at the Nara Institute of Science and Technology, Nara, Japan. He obtained his Ph.D. from the National Institute for Interdisciplinary Science and Technology (CSIR-NIIST), Trivandrum, India. His research interests are in the synthesis and self-assembly of organic as well as plasmonic nanomaterials for the amplification of various spectroscopic signals. Takuya Nakashima is an Associate Professor at the Nara Institute of Science and Technology. He received his Ph.D. degree from Kyushu University in 2003. His research focuses on the synthesis and selfassembly of photofunctional materials including organic compounds as well as nanoparticles. Tsuyoshi Kawai is a Professor at the Nara Institute of Science and Technology. He obtained his Ph.D. from Osaka University in 1993. His current research interests focus on the development of photoluminescent and photoreactive materials and their physicochemical properties. http://mswebs.naist.jp/LABs/kawai/english/index. html 3450



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Fluorescent Chiral Binaphtylene−Perylenebiscarboxydiimide Dimer. ChemPhysChem 2007, 8, 1465−1468. (21) Langhals, H.; Hofer, A.; Bernhard, S.; Siegel, J. S.; Mayer, P. Axially Chiral Bichromophoric Fluorescent Dyes. J. Org. Chem. 2011, 76, 990−992. (22) Nakabayashi, K.; Amako, T.; Tajima, N.; Fujiki, M.; Imai, Y. Nonclassical Dual Control of Circularly Polarized Luminescence Modes of Binaphthyl-Pyrene Organic Fluorophores in Fluidic and Glassy Media. Chem. Commun. 2014, 50, 13228−13230. (23) Amako, T.; Nakabayashi, K.; Suzuki, N.; Guo, S.; Rahim, N. A.; Harada, T.; Fujiki, M.; Imai, Y. Pyrene Magic: Chiroptical Enciphering and Deciphering 1,3-Dioxolane Bearing Two Wirepullings to Drive Two Remote Pyrenes. Chem. Commun. 2015, 51, 8237−8240. (24) Walters, R. S.; Kraml, C. M.; Byrne, N.; Ho, D. M.; Qin, Q.; Coughlin, F. J.; Bernhard, S.; Pascal, R. A. Configurationally Stable Longitudinally Twisted Polycyclic Aromatic Compounds. J. Am. Chem. Soc. 2008, 130, 16435−16441. (25) Morisaki, Y.; Inoshita, K.; Chujo, Y. Planar-Chiral ThroughSpace Conjugated Oligomers: Synthesis and Characterization of Chiroptical Properties. Chem. - Eur. J. 2014, 20, 8386−8390. (26) Morisaki, Y.; Gon, M.; Sasamori, T.; Tokitoh, N.; Chujo, Y. Planar Chiral Tetrasubstituted [2.2]Paracyclophane: Optical Resolution and Functionalization. J. Am. Chem. Soc. 2014, 136, 3350−3353. (27) Brittain, H.; Fendler, J. H. Enhanced Optical Activity Associated with Chiral 1-(1-Hydroxyhexy1)pyrene Excimer Formation. J. Am. Chem. Soc. 1980, 102, 6372−6374. (28) Sasaki, H.; Sisido, M.; Imanishi, Y. Distribution and Excimer Configurations of Pyrenyl Amphiphiles in Bicomponent Bilayer Membranes of Chiral Aromatic Amino Acid Amphiphiles. Langmuir 1991, 7, 1953−1957. (29) Kumar, J.; Nakashima, T.; Tsumatori, H.; Mori, M.; Naito, M.; Kawai, T. Circularly Polarized Luminescence in Supramolecular Assemblies of Chiral Bichromophoric Perylene Bisimides. Chem. Eur. J. 2013, 19, 14090−14097. (30) Kano, K.; Matsumoto, H.; Hashimoto, S.; Sisido, M.; Imanishi, Y. Chiral Pyrene Excimer in the Gamma-Cyclodextrin Cavity. J. Am. Chem. Soc. 1985, 107, 6117−6118. (31) Inouye, M.; Hayashi, K.; Yonenaga, Y.; Itou, T.; Fujimoto, K.; Uchida, T.; Iwamura, M.; Nozaki, K. A Doubly AlkynylpyreneThreaded [4]Rotaxane That Exhibits Strong Circularly Polarized Luminescence from the Spatially Restricted Excimer. Angew. Chem., Int. Ed. 2014, 53, 14392−14396. (32) Maeda, H.; Bando, Y.; Shimomura, K.; Yamada, I.; Naito, M.; Nobusawa, K.; Tsumatori, H.; Kawai, T. Chemical-Stimuli-Controllable Circularly Polarized Luminescence from Anion-Responsive πConjugated Molecules. J. Am. Chem. Soc. 2011, 133, 9266−9269. (33) Haketa, Y.; Bando, Y.; Takaishi, K.; Uchiyama, M.; Muranaka, A.; Naito, M.; Shibaguchi, H.; Kawai, T.; Maeda, T. Asymmetric Induction in the Preparation of Helical Receptor−Anion Complexes: Ion-Pair Formation with Chiral Cations. Angew. Chem., Int. Ed. 2012, 51, 7967−7971. (34) Maeda, H.; Bando, Y. Recent Progress in Research on StimuliResponsive Circularly Polarized Luminescence Based on π-Conjugated Molecules. Pure Appl. Chem. 2013, 85, 1967−1978. (35) Sánchez-Carnerero, E. M.; Moreno, F.; Maroto, B. L.; Agarrabeitia, A. R.; Ortiz, M. J.; Vo, B. G.; Muller, G.; de la Moya, S. Circularly Polarized Luminescence by Visible-Light Absorption in a Chiral O-BODIPY Dye: Unprecedented Design of CPL Organic Molecules from Achiral Chromophores. J. Am. Chem. Soc. 2014, 136, 3346−3349. (36) Kumar, J.; Nakashima, T.; Tsumatori, H.; Kawai, T. Circularly Polarized Luminescence in Chiral Aggregates: Dependence of Morphology on Luminescence Dissymmetry. J. Phys. Chem. Lett. 2014, 5, 316−321. (37) Tsumatori, H.; Nakashima, T.; Kawai, T. Observation of Chiral Aggregate Growth of Perylene Derivative in Opaque Solution by Circularly Polarized Luminescence. Org. Lett. 2010, 12, 2362−2365. (38) Kumar, J.; Tsumatori, H.; Yuasa, J.; Kawai, T.; Nakashima, T. Self-Discriminating Termination of Chiral Supramolecular Polymer-

ACKNOWLEDGMENTS This work was supported in part by the Grand-in-Aid for Scientific Research (No. 25248019) from JSPS. J.K. acknowledges JSPS for the postdoctoral fellowship.


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REFERENCES

(1) Addadi, L.; Weiner, S. Biomineralization: Crystals, Asymmetry and Life. Nature 2001, 411, 753−755. (2) Meldrum, F. C.; Colfen, H. Controlling Mineral Morphologies and Structures in Biological and Synthetic Systems. Chem. Rev. 2008, 108, 4332−4432. (3) Lorenzo, M. O.; Baddeley, C. J.; Muryn, C.; Raval, R. Extended Surface Chirality from Supramolecular Assemblies of Adsorbed Chiral Molecules. Nature 2000, 404, 376−379. (4) Hembury, G. A.; Borovkov, V. V.; Inoue, Y. Chirality-Sensing Supramolecular Systems. Chem. Rev. 2008, 108, 1−73. (5) Circular Dichroism: Principles and Applications; Nakanishi, K., Berova, N., Woody, R. W., Eds.; Wiley-VCH: New York, 2000. (6) Richardson, F. S.; Riehl, J. P. Circularly Polarized Luminescence Spectroscopy. Chem. Rev. 1977, 77, 773−792. (7) Riehl, J. P. Circularly Polarized Luminescence Spectroscopy. Chem. Rev. 1986, 86, 1−16. (8) Sanchez-Carnerero, E. M.; Agarrabeitia, A. R.; Moreno, F.; Maroto, B. L.; Muller, G.; Ortiz, M. J.; de la Moya, S. Circularly Polarized Luminescence from Simple Organic Molecules. Chem.−Eur. J. 2015, 21, n/a. (9) Muller, G. Circularly Polarized Luminescence. In Luminescence of Lanthanide Ions in Coordination Compounds and Nanomaterials; de Bettencourt-Dias, A., Eds.; John Wiley & Sons: Chichester, U.K., 2014; Chapter 3, pp 77− 124. (10) Blok, P. M. L.; Dekkers, H. P. J. M. Discrimination between 3 ππ* and 3nπ* States in Organic Molecules by Circular Polarization of Phosphorescence. Chem. Phys. Lett. 1989, 161, 188−194. (11) Nakanishi, T.; Naito, M.; Takeoka, Y.; Matsuura, K. Versatile Self-Assembled Hybrid Systems with Exotic Structures and Unique Functions. Curr. Opin. Colloid Interface Sci. 2011, 16, 482−490. (12) Carr, R.; Evans, N. H.; Parker, D. Lanthanide Complexes as Chiral Probes Exploiting Circularly Polarized Luminescence. Chem. Soc. Rev. 2012, 41, 7673−7686. (13) Lunkley, J. L.; Shirotani, D.; Yamanari, K.; Kaizaki, S.; Muller, G. Extraordinary Circularly Polarized Luminescence Activity Exhibited by Cesium Tetrakis(3-heptafluoro-butylryl-(+)-camphorato) Eu(III) Complexes in EtOH and CHCl3 Solutions. J. Am. Chem. Soc. 2008, 130, 13814−13815. (14) De Greef, T. F. A.; Smulders, M. M. J.; Wolffs, M.; Schenning, A. P. H. J.; Sijbesma, R. P.; Meijer, E. W. Supramolecular Polymerization. Chem. Rev. 2009, 109, 5687−5754. (15) Babu, S. S.; Kartha, K. K.; Ajayaghosh, A. Excited State Processes in Linear π-System-Based Organogels. J. Phys. Chem. Lett. 2010, 1, 3413−3424. (16) Field, J. E.; Muller, G.; Riehl, J. P.; Venkataraman, D. Circularly Polarized Luminescence from Bridged Triarylamine Helicenes. J. Am. Chem. Soc. 2003, 125, 11808−11809. (17) Sawada, Y.; Furumi, S.; Takai, A.; Takeuchi, M.; Noguchi, K.; Tanaka, K. Rhodium-Catalyzed Enantioselective Synthesis, Crystal Structures, and Photophysical Properties of Helically Chiral 1,1′Bitriphenylenes. J. Am. Chem. Soc. 2012, 134, 4080−4083. (18) Goto, K.; Yamaguchi, R.; Hiroto, S.; Ueno, H.; Kawai, T.; Shinokubo, H. Intermolecular Oxidative Annulation of 2-Aminoanthracenes to Diazaacenes and Aza[7]helicenes. Angew. Chem., Int. Ed. 2012, 51, 10333−10336. (19) Sakai, H.; Shinto, S.; Kumar, J.; Araki, Y.; Sakanoue, T.; Takenobu, T.; Wada, T.; Kawai, T.; Hasobe, T. Highly Fluorescent [7]Carbohelicene Fused by Asymmetric 1,2-Dialkyl-Substituted Quinoxaline for Circularly Polarized Luminescence and Electroluminescence. J. Phys. Chem. C 2015, 119, 13937−13947. (20) Kawai, T.; Kawamura, K.; Tsumatori, T.; Ishikawa, M.; Naito, M.; Fujiki, M.; Nakashima, T. Circularly Polarized Luminescence of a 3451




Perspective

(56) Watanabe, K.; Osaka, I.; Yorozuya, S.; Akagi, K. Helically πStacked Thiophene-Based Copolymers with Circularly Polarized Fluorescence: High Dissymmetry Factors Enhanced by Self Ordering in Chiral Nematic Liquid Crystal Phase. Chem. Mater. 2012, 24, 1011− 1024. (57) Satrijo, A.; Meskers, S. J. S.; Swager, T. M. Probing a Conjugated Polymer’s Transfer of Organization-Dependent Properties from Solutions to Films. J. Am. Chem. Soc. 2006, 128, 9030−9031. (58) 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. (59) Nakano, Y.; Ichiyanagi, F.; Naito, M.; Yang, Y.; Fujiki, M. Chiroptical Generation and Inversion during the Mirror-SymmetryBreaking Aggregation of Dialkylpolysilanes Due to Limonene Chirality. Chem. Commun. 2012, 48, 6636−6638. (60) Nagata, Y.; Nishikawa, T.; Suginome, M. Chirality-Switchable Circularly Polarized Luminescence in Solution Based on the SolventDependent Helix Inversion of Poly(Quinoxaline-2,3-Diyl)s. Chem. Commun. 2014, 50, 9951−9953. (61) Hayasaka, H.; Miyashita, T.; Tamura, K.; Akagi, K. Helically πStacked Conjugated Polymers Bearing Photoresponsive and Chiral Moieties in Side Chains: Reversible Photoisomerization-Enforced Switching Between Emission and Quenching of Circularly Polarized Fluorescence. Adv. Funct. Mater. 2010, 20, 1243−1250. (62) Tohgha, U.; Deol, K. K.; Porter, A. G.; Bartko, S. G.; Choi, J. K.; Leonard, B. M.; Varga, K.; Kubelka, J.; Muller, G.; Balaz, M. Ligand Induced Circular Dichroism and Circularly Polarized Luminescence in CdSe Quantum Dots. ACS Nano 2013, 7, 11094−11102. (63) Naito, M.; Iwahori, K.; Miura, A.; Yamane, M.; Yamashita, I. Circularly Polarized Luminescent CdS Quantum Dots Prepared in a Protein Nanocage. Angew. Chem., Int. Ed. 2010, 49, 7006−7009. (64) Harada, T.; Kajiyama, N.; Ishizaka, K.; Toyofuku, R.; Izumi, K.; Umemura, K.; Imai, Y.; Taniguchic, N.; Mishima, K. Plasmon Resonance-Enhanced Circularly Polarized Luminescence of SelfAssembled Meso-tetrakis-(4-sulfonatophenyl)porphyrin−Surfactant Complexes in Interaction with Ag Nanoparticles. Chem. Commun. 2014, 50, 11169−11172. (65) Yeom, J.; Yeom, B.; Chan, H.; Smith, K. W.; DominguezMedina, S.; Bahng, J. H.; Zhao, G.; Chang, W.-S.; Chang, S.-J.; Chuvilin, A.; et al. Chiral Templating of Self-Assembling Nanostructures by Circularly Polarized Light. Nat. Mater. 2015, 14, 66−72. (66) Mukhina, M. V.; Maslov, V. G.; Baranov, A. V.; Fedorov, A. V.; Orlova, A. O.; Purcell-Milton, F.; Govan, J.; Gun’ko, Y. K. Intrinsic Chirality of CdSe/ZnS Quantum Dots and Quantum Rods. Nano Lett. 2015, 15, 2844−2851. (67) Maoz, B. M.; Chaikin, Y.; Tesler, A. B.; Bar Elli, O.; Fan, Z.; Govorov, A. O.; Markovich, G. Amplification of Chiroptical Activity of Chiral Biomolecules by Surface Plasmons. Nano Lett. 2013, 13, 1203− 1209.

ization: Tuning the Length of Nanofibers. Angew. Chem., Int. Ed. 2015, 54, 5943−5947. (39) Ikeda, T.; Masuda, T.; Hirao, T.; Yuasa, J.; Tsumatori, H.; Kawai, T.; Haino, T. Circular Dichroism and Circularly Polarized Luminescence Triggered by Self-Assembly of Tris(phenylisoxazolyl)benzenes Possessing a Perylenebisimide Moiety. Chem. Commun. 2012, 48, 6025−6027. (40) Phillips, K. E. S.; Katz, T. J.; Jockusch, S.; Lovinger, A. J.; Turro, N. J. Synthesis and Properties of an Aggregating Heterocyclic Helicene. J. Am. Chem. Soc. 2001, 123, 11899−11907. (41) Riehl, J. P.; Richardson, F. S. Circularly Polarized Luminescence. Methods Enzymol 1993, 226, 539−553. (42) Katayama, K.; Hirata, S.; Vacha, M. Circularly Polarized Luminescence from Individual Microstructures of Conjugated Polymer Aggregates with Solvent-Induced Chirality. Phys. Chem. Chem. Phys. 2014, 16, 17983−17987. (43) Kaseyama, T.; Furumi, S.; Zhang, X.; Tanaka, K.; Takeuchi, M. Hierarchical Assembly of a Phthalhydrazide-Functionalized Helicene. Angew. Chem., Int. Ed. 2011, 50, 3684−3687. (44) Shen, Z.; Wang, T.; Shi, L.; Tang, Z.; Liu, M. Strong Circularly Polarized Luminescence from the Supramolecular Gels of an Achiral Gelator: Tunable Intensity and Handedness. Chem. Sci. 2015, 6, 4267−4272. (45) Gopal, A.; Hifsudheen, M.; Furumi, S.; Takeuchi, M.; Ajayaghosh, A. Thermally Assisted Photonic Inversion of Supramolecular Handedness. Angew. Chem., Int. Ed. 2012, 51, 10505− 10509. (46) Liu, J.; Su, H.; Meng, L.; Zhao, Y.; Deng, C.; Ng, J. C. Y.; Lu, P.; Faisal, M.; Lam, J. W. Y.; Huang, X.; et al. What Makes Efficient Circularly Polarised Luminescence in the Condensed Phase: Aggregation-Induced Circular Dichroism and Light Emission. Chem. Sci. 2012, 3, 2737−2747. (47) Li, H.; Cheng, J.; Deng, H.; Zhao, E.; Shen, B.; Lam, J. W. Y.; Wong, K. S.; Wu, H.; Li, B. S.; Tang, B. Z. Aggregation-induced chirality, circularly polarized luminescence, and helical self-assembly of a leucine-containing AIE luminogen. J. Mater. Chem. C 2015, 3, 2399− 2404. (48) Li, H.; Cheng, J.; Zhao, Y.; Lam, J. W. Y.; Wong, K. S.; Wu, H.; Li, B. S.; Tang, B. Z. L-Valine Methyl Ester-Containing Tetraphenylethene: Aggregation-Induced Emission, Aggregation-Induced Circular Dichroism, Circularly Polarized Luminescence, and Helical SelfAssembly. Mater. Horiz. 2014, 1, 518−521. (49) Spano, F. C.; Zhao, Z.; Meskers, S. C. J. Analysis of the Vibronic Fine Structure in Circularly Polarized Emission Spectra from Chiral Molecular Aggregates. J. Chem. Phys. 2004, 120, 10594−10604. (50) Spano, F. C.; Meskers, S. C. J.; Hennebicq, E.; Beljonne, D. Probing Excitation Delocalization in Supramolecular Chiral Stacks by Means of Circularly Polarized Light: Experiment and Modeling. J. Am. Chem. Soc. 2007, 129, 7044−7054. (51) Spano, F. C.; Meskers, S. C. J.; Hennebicq, E.; Beljonne, D. Using Circularly Polarized Luminescence to Probe Exciton Coherence in Disordered Helical Aggregates. J. Chem. Phys. 2008, 129, 024704− 024714. (52) Tempelaar, R.; Stradomska, A.; Knoester, J.; Spano, F. C. Circularly Polarized Luminescence as a Probe for Long-Range Interactions in Molecular Aggregates. J. Phys. Chem. B 2011, 115, 10592−10603. (53) Chen, S. H.; Katsis, D.; Schmid, A. W.; Mastrangelo, J. C.; Tsutsui, T.; Blanton, T. N. Circularly Polarized Light Generated by Photoexcitation of Luminophores in Glassy Liquid-Crystal Films. Nature 1999, 397, 506−508. (54) Geng, Y.; Trajkovska, A.; Katsis, D.; Ou, J. J.; Culligan, S. W.; Chen, S. H. Synthesis, Characterization, and Optical Properties of Monodisperse Chiral Oligofluorenes. J. Am. Chem. Soc. 2002, 124, 8337−8347. (55) Wilson, J. N.; Steffen, W.; McKenzie, T. G.; Lieser, G.; Oda, M.; Neher, D.; Bunz, U. H. F. Chiroptical Properties of Poly(pphenyleneethynylene) Copolymers in Thin Films: Large g−Values. J. Am. Chem. Soc. 2002, 124, 6830−6831. 3452


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