Abstract:In this study, we selectively modified a single meta-position of the tris-2,4,6-trichlorophenylmethyl (TTM) radical using non-conjugated donor (N,N-dimethyl group, –N(Me)₂) and acceptor (-Br, –NO₂) groups, resulting in three new TTM-type radicals: TTM-N(Me)₂, TTM-Br, and TTM-NO₂. Our findings indicated that, after the non-conjugated acceptors (-Br, -NO₂) directly attached to meta-position of TTM, there are no significant photophsical effect for TTM-Br, while TTM-NO₂ demonstrated a onefold increase in photostability and a threefold decrease in photoluminescent quantum yield (ФPL) compared to TTM. On the other hand, introducing a non-conjugated donor (-N(Me)2) at the meta position of TTM, endowed TTM-N(Me)₂ with a remarkable 10,475 fold increase in photostability and activated proton-induced fluorescence. These unique properties could be attributed to the small energy gap between frontier orbitals and the proximity of energy levels between the singly occupied molecular orbital (SOMO) and the highest doubly occupied molecular orbital (HDMO), as revealed by quantum chemistry calculations and photophysical properties analysis. Our results offer valuable insights into meta-substituted TTM-type radicals and provide a new avenue for studying asymmetric meta-substituted TTM radicals.

Keywords: Triphenylmethyl radical , Meta-substitution , Photostability , Proton-induced turn on fluorescence

Synthesis and photophysical properties of meta-position-substituted triphenylmethyl-type radicals with non-conjugated donor accepters.pdf