A simple strategy to simultaneously improve the lifetime and activity of classical iridium complex for photocatalytic water‐splitting

Abstract Herein, we design and synthesize a series of oligomers [Ir(ppy) 2 (dabpy)‐ODPA] n (D1‐n) by copolymerization of [Ir(ppy) 2 (dabpy)][PF 6 ] (D2) with 4,4′‐Oxydiphthalic anhydride (ODPA), to resolve the problem of simultaneous improvement of stability and activity of classical iridium complex for photocatalytic water‐splitting. Fourier‐transform infrared spectroscopy, X‐ray photoelectron spectroscopy, solid‐state nuclear magnetic resonance, and gel permeation chromatography results indicate that the degree of polymerization (n) of D1‐n could be tuned by the synthesis method. The best photocatalytic performance is reached by D1‐n with n at of 2 and/or 3 (D1‐2/3), which exhibits a photocatalytic lifetime up to 676 h and a photocatalytic hydrogen evolution of 162055.1 μmol·g ‐1 . Compared with classical iridium complex D2, the photocatalytic lifetime of D1‐2/3 is about 38 times longer and the photocatalytic activity is 1.3 times higher. Further increase of n leads to a decrease in both photocatalytic lifetime and activity. According to the spectroscopic characterizations, photoelectrochemical experiments, and density functional theory calculation, the significantly enhanced photocatalytic performance of D1‐2/3 originates from the oligomeric structure. The oligomer chain of D1‐2/3 with suitable length acts as a large steric hindrance to reduce the undesired photoinduced decomposition and prolong its lifetime. The possible coupling of adjacent Ir complexes in D1‐2/3 lowers the energy gap and increases the utilization of visible light, which overcomes the adverse effect of large steric hindrance and finally improve the activity. This work first provides a simple strategy for constructing oligomeric Ir photosensitizers to simultaneously achieve long lifetime and high activity, it will lay the foundation for the design of highly efficient photosensitizers in the future.