Recent Progress on Circularly Polarized Luminescent Materials for Organic Optoelectronic Devices

Control over the handedness of circularly polarized luminescence (CPL) in supramolecular gels is of special significance in biology and optoelectronics; however, it still remains a great challenge to precisely and efficiently regulate the chirality of CPL. Herein, a chiral phenylalanine-derived hydrogelator and achiral coumarin derivatives can co-assemble into nanofibrous hydrogels with controllable chirality, and the handedness of CPL of these hydrogels can be efficiently inverted by coumarin derivatives through noncovalent interactions, which can be further tuned at will by incorporating metal ions into the co-assembly. The hydrogen bonds, coordination interactions, and steric hindrance are proved to be the crucial factors for the CPL inversion. This study provides feasible strategies to efficiently regulate the handedness of CPL through co-assembly, and these CPL materials may have potential applications in the fields of photoelectric devices, smart chiroptical materials, and biological systems.

Inversion of Circularly Polarized Luminescence of Nanofibrous Hydrogels through Co-assembly with Achiral Coumarin Derivatives.

Circularly polarized luminescence in chiral materials

Circularly polarized luminescence (CPL) has been under intense research for future applications in high resolution 3D display, smart sensors and information technologies. Different types of CPL materials have been developed, but neither the handedness nor the asymmetrical luminescence degree can be inferred from the material composition or the components. CPL materials with switchable handedness or emission wavelength play an important role, reducing the need for repetitive bottom-up synthesis. Herein will be presented, switchable CPL behaviors towards multiple reported stimuli, including light irradiation, host-guest interaction, metal ions, pH, solvent, temperature, etc. This summary and discussion of the effective stimuli is aimed to promote rational future material exploration and boost related multidisciplinary applications.

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The Progress and Perspective of Organic Molecules With Switchable Circularly Polarized Luminescence.

9,10-Bis(phenylethynyl)anthracenes (BPEAs) are an important class of dyes in various applications including chemiluminescence emitters, materials for photon upconversion, and for optoelectronic devices. Some of these applications require control over the packing modes of the molecules within the active layer, which can be effected by bottom-up self-assembly. Studies aimed at controlling the molecular organization of BPEAs have primarily focused on bulk or liquid-crystal materials, whereas in-depth investigations of BPEA-based assemblies in solution remain elusive. In this article, the self-assembly of two new BPEA derivatives with hydrophobic side chains is reported, one of them featuring amide functional groups and the other one lacking them. Comparison of the self-assembly behavior of both systems in solution using spectroscopic (UV/Vis, fluorescence, and NMR), microscopic (AFM), and theoretical (PM6) studies reveals the crucial role of the amide groups in controlling the self-assembly. For both systems, the formation of H-type face-to-face π-stacks is proposed, whereas the interplay of π-stacking and H-bonding is responsible for driving the formation of 1D stacks and increasing the binding constant by two to three orders of magnitude. Our findings show that H-bonding is a prerequisite to create ordered BPEA assemblies in solution.

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Self‐Assembly of 9,10‐Bis(phenylethynyl) Anthracene (BPEA) Derivatives: Influence of π–π and Hydrogen‐Bonding Interactions on Aggregate Morphology and Self‐Assembly Mechanism

A new optical material based on the self-assembly of a low-molecular organogelator-linked anthracene derivative for the control of the fluorescence wavelength and polarization was developed. When the anthracene derivative was formed through self-assembly, the fluorescence wavelength was shifted by 100 nm (426 to 526 nm) and emitted circularly polarized luminescence. The control of the fluorescence wavelength and polarization was accomplished through the excimer formation of anthracene fluorophores, which can be tuned by the cooling process, temperature and solvent of the solution. Also, the fluorescence control in the solid state and the white-light emission in the gel state were accomplished by mixing the polymer matrix, and the addition of red-emitting dye, respectively. This material has possible potential for various applications such as a spectral conversion film, white light-emitting diodes and circularly polarized displays.

Yudai Yoshigashima

Papers

Tunable Stokes shift and circularly polarized luminescence by supramolecular gel