The photophysical properties of two positional isomers of dinaphthyl‐9‐phenylcarbazoles (2,7‐DNpPCz and 3,6‐DNpPCz) were systematically investigated in solution and solid states. Experimental measurements revealed a pronounced positional dependence, although both compounds exhibit fluorescence in solution and the solid state. On average, the 2,7‐isomers exhibit larger fluorescence rate values than the 3,6‐isomers, although the magnitude of this difference varies among individual compounds. To gain mechanistic insight, density function theory (DFT) and time‐dependence DFT calculations were performed at the (TD)‐B3LYP/6‐31+G(d) level. The results show that 2,7‐DNpPCz derivatives possess delocalized frontier orbitals and large oscillator strengths for the S 1 ← S 0 transition, whereas 3,6‐DNpPCz derivatives exhibit smaller oscillator strengths with mixed orbital contributions, leading to weaker transition probabilities. These combined findings demonstrate that substitution geometry critically governs radiative decay dynamics in carbazole‐based luminophores and provide valuable guidelines for the molecular design of efficient solid‐state organic emitters.
Yamaji et al. (Sun,) studied this question.