Ring-fused BODlPY Derived Heavy-Atom-Free Triplet Photosensitizers

Abstract

Triplet photosensitizers are compounds that demonstrate strong absorption of the excitation light, high intersystem crossing (ISC) efficiency for efficient triplet state generation, and long triplet lifetimes to facilitate subsequent photochemical reactions. Among these, heavy-atom-free triplet photosensitizers have attracted particular attention due to their advantages of long-lived triplet states and low dark toxicity in comparison with those heavy-atom-containing photosensitizers. Owing to the superior photophysical and chemical characteristics, boron dipyrromethene (BODIPY) dyes have been developed as promising heavy-atom-free triplet photosensitizers through specific molecular design strategies. However, many heavy-atom-free BODIPY-based photosensitizers exhibit relatively short excitation wavelengths in the visible-light region, and their ISC efficiencies dropped significantly with the extending of π-conjugation via the Knoevenagel condensation reaction. Recently, ring-fused BODIPY skeleton provides a feasible approach for the design of long-wavelength NIR photosensitizers. This review provides a comprehensive summary of the strategies utilized for the construction of ring-fused BODIPY-based photosensitizers including the installation of a twisted π-conjugation framework, the fusion of thiophene moieties and the formulation of an aggregation-induced ISC process. Meanwhile, some important spectroscopic and photophysical properties of these photosensitizers, along with their related applications, are also described.