A direct observation of up-converted room-temperature phosphorescence in an anti-Kasha dopant-matrix system
Jiuyang Li, Xun Li, Guangming Wang, Xuepu Wang, Minjian Wu, Jiahui Liu, Kaka Zhang
Abstract
Abstract It is common sense that emission maxima of phosphorescence spectra ( λ P ) are longer than those of fluorescence spectra ( λ F ). Here we report a serendipitous finding of up-converted room-temperature phosphorescence (RTP) with λ P < λ F and phosphorescence lifetime > 0.1 s upon doping benzophenone-containing difluoroboron β - diketonate (BPBF 2 ) into phenyl benzoate matrices. The up-converted RTP is originated from BPBF 2 ’s T n ( n ≥ 2) states which show typical 3 n-π* characters from benzophenone moieties. Detailed studies reveal that, upon intersystem crossing from BPBF 2 ’s S 1 states of charge transfer characters, the resultant T 1 and T n states build T 1 -to-T n equilibrium. Because of their 3 n-π* characters, the T n states possess large phosphorescence rates that can strongly compete RTP(T 1 ) to directly emit RTP(T n ) which violates Kasha’s rule. The direct observation of up-converted RTP provides deep understanding of triplet excited state dynamics and opens an intriguing pathway to devise visible-light-excitable deep-blue afterglow emitters, as well as stimuli-responsive afterglow materials.