Minimized ΔEST: drive thermally activated delayed fluorescence materials in photodynamic therapy

Abstract

The energy gap (ΔE_ST) between the singlet state (S₁) and the triplet state (T₁) and the T₁ lifetime are important factors in determining the efficiency of photodynamic therapy (PDT). Owing to intersystem crossing (ISC) between S₁ and T₁, a smaller ΔE_ST becomes a key factor in the design of photosensitizers (PSs). Attractively, thermally activated delayed fluorescence (TADF) materials exhibit a small ΔE_ST, fully utilizing photon energy and achieving simultaneous improvement in both the energy gap and lifetime. However, the applicability of TADF in complex intracellular environments remains to be explored. In this review, the ingenious design of TADF molecules is presented according to group classification, and elaborate strategies of TADF are discussed in promoting triplet energy conversion, improving the penetration depth of phototherapy, and regulating the dynamic balance of triplet excitons. This article comprehensively summarizes the development of TADF materials in PDT, which has important reference value for investigating TADF PSs.