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Time-Dependent Afterglow Color in a Single-Component Organic Molecular Crystal
Jian-Xin Wang1, Ye-Guang Fang2, Chun-Xiang Li2
1Institution Key Laboratory of Radiopharmaceuticals, College of Chemistry, Beijing Normal University, Beijing, 100875, P. R. China.
Abstract:
An organic crystal of 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (pCBP) exhibits time-dependent afterglow color from blue to orange over 1 s. Both experimental and computational data confirm that the color evolution results from well-separated, long-persistent thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP) with different but comparable decay rates. TADF is enabled by a small S1 -T1 energy gap of 0.7 kcal mol-1 . The good separation of TADF and RTP is due to a 11.8 kcal mol-1 difference in the S0 energies of the S1 and T1 structures, indicating that apart from the excited-state properties, tuning the ground state is also important for luminescence properties. This afterglow color evolution of pCBP allows its applications in anticounterfeiting and data encryption with high security levels.
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