Effect of anchoring groups on the photocatalytic performance of iridium(iii) complexes in hydrogen production and their toxicological analysis

Three iridium(iii) complexes (Ir1-Ir3) with different anchoring moieties, namely, 4,4′-dinitro-2,2′-bipyridine, tetraethyl [2,2′-bipyridine]-4,4′-diylbis(phosphonate) and diethyl [2,2′-bipyridine]-4,4′-dicarboxylate were designed, synthesised and used as photosensitisers for water-splitting hydrogen generation. The influence of these anchoring moieties on the photophysical and electrochemical characteristics of the Ir(iii) complexes was investigated via density functional theory (DFT) simulations and experimental methods. The hydrogen production efficiency of the Ir1@Pt-TiO2 system was as high as 4020.27 mol μg⁻¹ h⁻¹. Among the three anchoring moieties, tetraethyl [2,2′-bipyridine]-4,4′-diylbis(phosphonate) improved the performance of the complexes to the greatest extent. Toxicological investigation revealed that the toxicity of the Ir(iii) complexes to luminous bacteria did not differ significantly from that of TiO₂, implying that the Ir(iii) complexes synthesised in this study do not pose a significant threat to marine environments, similar to TiO₂. This finding has potential implications for the development of highly efficient Ir(iii) photosensitisers to be used in the water-splitting process required for hydrogen production.