Heavy Atom Effect on Tn (n ≥ 2) Afterglow

Abstract

The properties of higher triplet excited states (Tn, n ≥ 2) are essential for deep understanding of excited state dynamics, but direct observation of Tn phosphorescence remains rare, let alone systematic studies of Tn behaviors based on well‐designed luminescence molecules. Recently, a serendipitous finding of Tn (n ≥ 2) afterglow (phosphorescence lifetime > 0.1 s) in benzophenone‐containing difluoroboron β‐diketonate (BPBF2) system is communicated. Here Cl/Br/I atoms are covalently incorporated into BPBF2 molecules and report the first systematic study of heavy atom effect (HAE) on Tn (n ≥ 2) afterglow. It is known that Cl/Br/I HAE has been widely reported and thoroughly studied in T1 afterglow systems, which shows that Br atom is usually the optimized selection for balancing T1 afterglow efficiency and lifetime. In contrast, the covalent linkage of Br atom to BPBF2 has been found to dramatically suppress Tn (n ≥ 2) afterglow. The experimental emission intensity(T2)/intensity(T1) ratios are positively correlated with kIC(T1−T2)/kIC(T2−T1) × kP(T2)/kP(T1), where kIC and kP refer to the rates of calculated internal conversion and phosphorescence emission. These fundamental studies would be helpful for elucidating the panorama of Perrin‐Jablonski diagram of organic systems and provide intriguing Tn (n ≥ 2) afterglow materials for future applications.