Synergistic Effects of Siloxy and Silylmethoxy Moieties on Room-Temperature Phosphorescence of 1,4-Dibenzoylbenzene Luminophores

Abstract

Rare-metal-free luminophores that exhibit room-temperature phosphorescence (RTP) in the solid state and polymer film have attracted significant attention in various fields, including imaging, sensing, and optoelectronic technologies. Herein 1,4-dibenzolyl-2-siloxy-5-(silylmethoxy)benzenes are reported as novel RTP luminophores. Thermal analysis reveals that the unsymmetrical molecular structure of the benzene derivatives results in lower melting points compared to their symmetrical counterparts. Their solid-state RTP is highly dependent on the siloxy group. The choice of tert-BuPh₂SiO group is essential for achieving efficient RTP in the microcrystalline state; the quantum yields ranged from 0.40 to 0.58, unlike the choice of tert-BuMe₂SiO. Notably, poly(methyl methacrylate) films doped with the benzene derivatives emitted RTP under vacuum conditions with quantum yields ranging from 0.06 to 0.09, irrespective of the siloxy group. Theoretical calculations suggest that the RTP occurs via excitation involving intramolecular charge-transfer from the siloxy and silylmethoxy moieties to the benzoyl groups, followed by intersystem crossing from the lowest singlet excited state (S₁) to the second-lowest triplet excited state (T₂), and subsequent internal conversion to the lowest excited triplet state (T₁). Furthermore, the polymer film doped with one of the benzene derivatives is demonstrated to function as a molecular oxygen scavenger within a polymer matrix.