Single Molecular Persistent Room‐Temperature Phosphorescence and Circularly Polarized Luminescence from Binaphthol‐Decorated Optically Innocent Cyclotriphosphazenes

Abstract

Circularly polarized luminescence (CPL) features of BINOL‐decorated cyclotriphosphazenes are reported for the very first time. The luminescence dissymmetry factor (glum) of these compounds in chloroform solutions and 1 % polymethyl methacrylate (PMMA) matrix are found to be 1.0 x 10‐3, and 2.9 x 10‐3, respectively. However, no CPL signal is observed for the pristine solids. The enantiomers (R/S) show ultraviolet photoluminescence (~ 350‐360 nm) in solution and solid state. These compounds show ~ 10 times larger absolute photoluminescence quantum yield (PLQY) than the simple BINOLs in the solutions state. In solid‐state, cyclophosphazene‐(R) shows larger PLQY than binaphthol‐(R); in contrast, (S)‐enantiomer shows lower PLQY than binaphthol‐(S), which indicates that the isomer‐dependent solid‐state packing of these compounds plays a crucial role in controlling the PL. Thin films with more than 1 % doping concentration and pristine solids of these compounds do not show persistent room temperature phosphorescence (pRTP) due to concentration‐caused quenching. However, thin films (1 % PMMA) of these chiral emitters exhibit pRTP characteristics with a lifetime of ~ 159‐343 ms under vacuum. Detailed theoretical calculations reveal that the cyclophosphazene acts as an optically innocent dendritic core, and the optical features of these compounds are dictated by the pendent BINOL chromophore.