Tuning non-radiative decay channels via symmetric/asymmetric substituent effects on phenazine derivatives and their phototherapy switch between dynamic and thermal processes

Recently, research based on non-radiative decay processes leading to photodynamic therapy or photothermal therapy has become an attractive hotspot. Of particular importance is achieving better performance in photosensitive dye design. Herein, two comparable emitters (DEPZ-S and DEPZ-A) with the same electronic donor-acceptor segment were prepared, but their different symmetrical patterns caused different reactive oxygen species (ROS) generation capacity and photothermal conversion capacity, respectively, which indicates that their non-radiative decay channels could be switched between intersystem crossing (ISC) and thermal deactivation. Theoretical simulation exhibited coincident results, and their differentiated excited-state energy level distribution decided the non-radiative decay channels change: DEPZ-S with high intramolecular symmetry exhibited a larger spin-orbit coupling (SOC) matrix and smaller energy splitting (Delta E-ST) between singlet excited state and triplet excited state easily facilitating the ISC process, but asymmetric DEPZ-A with a narrow band gap (Delta E-S0S1) and big reorganization energy reduced the potential barrier of the thermal deactivation and increased its occurrence probability. After encapsulating two dyes with a hydrophilic polymer matrix to improve intake efficiency, both of them displayed good phototherapy treatment effect on bladder cancer cells through dynamic or thermal processes when light illuminated. This work provides a new strategy for tuning non-radiative decay channels via symmetric/asymmetric substituent effects to realize precise phototherapy.