Synthesis and Photophysical Studies of Dibenzophosphole Oxides with D–A–D Triad Structures

Abstract

Five, D–A–D triad type dibenzophosphole oxide (DBPO) derivatives, 1a–e, containing electron‐donating diarylamine or carbazole moieties at their 2‐ and 8‐positions were prepared to investigate relationships that exist between their molecular structures and photophysical properties. Analysis of the crystal structure of the 2,8‐bis(diphenylamino) derivative 1a, revealed that its DBPO moiety possesses quinoid‐like bond‐alternation. In addition, DBPO 1a emits relatively high intramolecular charge transfer (ICT) type photoluminescence (PL) in nonpolar solvents. In contrast, DBPO 1b, possessing two carbazol‐9‐yl groups, has higher PL quantum yields than does 1a especially in polar solvents and the solid state. Analysis of the PL decays profiles of toluene solutions of the 6‐membered cyclic acridin‐10‐yl and phenoxazin‐10‐yl‐substituted DBPOs 1c and 1d reveal the existence of long‐lived components, which likely corresponds to thermally‐activated delayed fluorescence (TADF) at r.t. At low temperature, TADF occurs in a toluene solution of 1d with a lifetime of 188 ms. The related 9‐ethylcarbazol‐3‐yl‐substituted DBPO 1e has a higher PL quantum yield and shorter luminescent lifetime than does 1b. The findings show that the fluorescence properties of DBPOs can be readily controlled by introducing donor moieties. This serves as useful information for developing strategies to design DBPO emitters.