Synthesis and Characterization of Zn-Salophen Complexes with Different D–A Distances: An Approach to Tuning the Intersystem-Crossing Process

A series of novel zinc-salophen (salophen = N, N′-phenylenebis(salicylimine)) complexes (Zn-1–4) with electron donor–acceptor (D–A) structure were synthesized and characterized using a triphenylamine structure as the electron donor. Zn-salophen complexes with the same substituent sites have been reported to exhibit significant CT properties. The design of the D–A structure and the increase in the number of benzene rings to increase the length of bridging groups have led to a reduction in the energy difference between charge separation singlet and triplet states, resulting in the production of reactive oxygen species (ROS) under light irradiation. The ability has been enhanced (in terms of the production of singlet oxygen (1O2), compared with Zn-salophen, Zn-4 is 1.58 times higher). This method has been reported to enhance the intersystem crossing process of compounds, thereby enabling them to reach a triple excited state, but the generation of ROS has not been studied. Although the enhancement is not very significant, it has expanded the medical application prospects of these types of complexes and has provided a new strategy to enhance the production of ROS.