TLD1433 is the first Ru(II) complex to be tested as a photodynamic therapy agent in a clinical trial. In this contribution we study TLD1433 in the context of structurally‐related Ru(II)‐imidozo[4,5‐f][1,10]phenanthroline (ip) complexes appended with thiophene rings to decipher the unique photophysical properties which are associated with increasing oligothiophene chain length. Substitution of the ip ligand with ter‐ or quaterthiophene changes the nature of the long‐lived triplet state from metal‐to‐ligand charge‐transfer to 3ππ* character. The addition of the third thiophene thus presents a critical juncture which not only determines the photophysics of the complex but most importantly its capacity for 1O2 generation and hence the potential of the complex to be used as a photocytotoxic agent.

A series of three Ru(II) polypyridine complexes was investigated for the selective photocatalytic oxidation of NAD(P)H to NAD(P) + in water. A combination of (timeresolved) spectroscopic studies and photocatalysis experiments revealed that ligand design can be used to control the mechanism of the photooxidation: For prototypical Ru(II) complexes a 1 O 2 pathway was found. Rudppz ([(tbbpy) 2 Ru(dppz)]Cl 2 , tbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine, dppz = dipyrido[3,2-a:2',3'-c]phenazine), instead, initiated the cofactor oxidation by electron transfer from NAD(P)H enabled by supramolecular binding between substrate and catalyst. Expulsion of the photoproduct NAD (P) + from the supramolecular binding site in Rudppz allowed very efficient turnover. Therefore, Rudppz permits repetitive selective assembly and oxidative conversion of reduced naturally occurring nicotinamides by recognizing the redox state of the cofactor under formation of H 2 O 2 as additional product. This photocatalytic process can fuel discontinuous photobiocatalysis.