Synthesis and Properties of Optically Active X-Shaped Compounds With Electron-Withdrawing Groups Based on Planar
Hikari Harada1, Kazunori Okamoto1, Yasuhiro Morisaki1
1Department of Applied Chemistry for Environment, School of Biological and Environmental Sciences, Kwansei Gakuin University, Sanda, Hyogo, Japan.
None:
In this study, we report a systematic investigation of substituent-controlled chiroptical properties in planar chiral [2.2]paracyclophane-based X-shaped π-conjugated systems bearing CF3, CN, and NO2 groups. Despite nearly identical absorption maxima, the derivatives exhibit markedly different circular dichroism (CD) and circularly polarized luminescence (CPL) responses. The CN derivative, possessing moderate charge-transfer (CT) character, exhibits the highest |gabs| and |glum| values. In contrast, the strongly electron-withdrawing NO2 substituent substantially stabilizes the LUMO and enhances excited-state interactions, leading to reduced rotational strength and facilitated nonradiative decay. Solvent-dependent emission studies further reveal excited-state switching between locally excited (LE) and CT-dominated configurations in the NO2 derivative. Notably, the NO2 derivative exhibits crystallization-induced emission enhancement (CIEE), resulting in a marked increase in emission efficiency.
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