Synthesis of TADF photosensitizers with aggregation-induced emission properties for theranostics

Abstract

In recent years, materials featuring thermally active delayed fluorescence (TADF) have attracted significant attention, particularly in their application in organic light-emitting diodes (OLEDs). However, the potential of TADF materials for other scientific fields has been quickly recognized, most notably in biomedicine. TADF involves the upconversion of triplet excitons to the first excited singlet state from the first excited triplet state through reverse intersystem crossing (RISC). Essential for an efficient RISC process is a small singlet-triplet energy gap (ΔEST) The resulting emission therefore combines the prompt fluorescence from the initial singlet excitons and the delayed fluorescence originating from the excitons that have undergone RISC. All-organic TADF materials offer inexpensiveness, environmental friendliness, and low biotoxicity, making them promising alternatives for bioimaging and photodynamic therapy (PDT). Further, in recent studies TADF materials have been successfully applied as theranostics, combining both applications. By now, solely few examples of TADF materials have been tested in photodynamic therapy, however, with great success. However, the main challenges faced are that of dye leakage, lack of solubility in biological environment, lack of selectivity in targeting, and aggregation-caused quenching. The objective of this project is the development of small molecular donor-acceptor type TADF materials that feature aggregation induced emission (AIE) characteristics for the application in theranostics. Therefore, three acceptor molecules, AQ, BIQ, and ANP, were selected as building blocks due to their promising AIE characteristics, alongside derivatives of two well-known donor molecules, Cz-NH2, and TPA-NH2. It was found that the BIQ-Cz-NH2 emitter exhibited the most promising AIE-TADF characteristics, showing great potential for bioimaging.