It Takes Three to Tango - the length of the oligothiophene determines the nature of the long-lived excited state and the resulting photocytotoxicity of a Ru(II) photodrug.

Unlabelled: 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 ππ* 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 O generation and hence the potential of the complex to be used as a photocytotoxic agent.

Entry For The Table Of Contents: A low-lying triplet intraligand state (IL) determines the properties of the long-lived excited states in a series of Ru(II) complexes. The IL state can be accessed by increasing the length of an oligothiophene chain. The IL state is extremely efficient at generating O and thus enhances the potency of the complexes as PDT agents.