A new family of Ir(III) complexes were synthesised and employed as light-induced hydrogen-production photosensitisers in aqueous systems, where hydrogen evolution was observed only when the PS* was reduced by the sacrificial agent, NEt3, signifying that a minimum potential difference of >0.2 V between E(PS*/PS(-)) and E(NEt3(+)/NEt3) is required for efficient hydrogen production [i.e., E(PS*/PS(-)) >1.19 V versus NHE]. The analytical method developed here is demonstrated to be useful for screening new photosensitisers for light-driven hydrogen generation.