Key of Suppressed Triplet Nonradiative Transition-Dependent Chemical Backbone for Spatial Self-Tunable Afterglow

Abstract

Highly efficient persistent (lifetime > 0.1 s) room-temperature phosphorescence (<i>p</i>RTP) chromophores are important for futuristic high-resolution afterglow imaging for state-of-the-art security, analytical, and bioimaging applications. Suppression of the radiationless transition from the lowest triplet excited state (T₁) of the chromophores is a critical factor to access the high RTP yield and RTP lifetime for desirable <i>p</i>RTP. Logical explanations for factor suppression based on chemical structures have not been reported. Here we clarify a strategy to reduce the radiationless transition from T₁ based on chemical backbones and yield a simultaneous high RTP yield and high RTP lifetime. Yellow phosphorescence chromophores that contain a coronene backbone were synthesized and compared with yellow phosphorescent naphthalene. One of the designed coronene derivatives reached a RTP yield of 35%, which is the best value for chromophores with a RTP lifetime of 2 s. The optically measured rate constant of a radiationless transition from T₁ was correlated precisely with a multiplication of vibrational spin-orbit coupling (SOC) at a T₁ geometry and with the Franck-Condon chromophore factor. The agreement between the experimental and theoretical results confirmed that the extended two-dimensional fused structure in the coronene backbone contributes to a decrease in vibrational SOC and Franck-Condon factor between T₁ and the ground state to decrease the radiationless transition. A resolution-tunable afterglow that depends on excitation intensity for anticounterfeit technology was demonstrated, and the resultant chromophores with a high RTP yield and high RTP lifetime were ideal for largely changing the resolution using weak excitation light.