Three π-conjugated biphenyl/terphenyl-containing TTM-based organic radicals were synthesized. Radicals exhibit strong red luminescence even in the highly polar solvent tetrahydrofuran. Studies showed that nonlinear conjugation between substituent groups and TTM would increase the degree of hybridization between the charge transfer and ground state, thus increasing photoluminescence quantum yield. In contrast, linear conjugation enhances the photostability of radicals.

This study focuses on the impact of alternant phenyl substituents on the photophysical properties of tris-(2,4,6-trichlorophenyl)methyl (TTM)-type radicals. Most donor–acceptor-type luminescent systems show solvent-polarity sensitivity, which limits their applications. Herein, three alternate π-conjugated biphenyl/terphenyl substituents are attached to the TTM unit. Results reveal that connection modes and types of benzene ring derivatives lead to distinct charge transfer (CT) and locally excited state hybrid emitters due to the differences in conjugation degree. All three radicals exhibit polarity-insensitive red emission (626–690 nm), and their photoluminescence quantum yields (PLQYs) increase with solvent polarity. Specifically, linear-conjugated TTM-DPh has higher photostability but lower PLQY, while nonlinear-conjugated TTM-3DPh and TTM-TPh have nearly 10-fold higher PLQYs. The photophysical studies suggest that the conjugation degree and hybridization level between CT and ground states account for these properties.