Abstract
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 (3)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 (1)O(2) 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 ((3)IL) determines the properties of the long-lived excited states in a series of Ru(II) complexes. The (3)IL state can be accessed by increasing the length of an oligothiophene chain. The (3)IL state is extremely efficient at generating (1)O(2) and thus enhances the potency of the complexes as PDT agents.