Author’s Pre-Print Version 1 A theoretical exploration of TypeI/TypeII dual photoreactivity of new promising Ru(II)-dyads for PDT approach M.E.Alberto,* a J. Pirillo, b N.Russo, b C. Adamo a,c a Chimie ParisTech, PSL Research University, CNRS, Institut de Recherche de Chimie Paris (IRCP), F-75005 Paris, France. E-mail: marta.alberto@chimie-paristech.fr b Dipartimento di Chimica e Tecnologie Chimiche, Università della Calabria, Via P. Bucci, 87036 Rende, Italy c Institut Universitaire de France, 103 Boulevard Saint Michel, F-75005 Paris, France KEYWORDS: PhotoDynamicTherapy, Singlet Oxygen, Ru(II)-dyads, α-oligothiophenes, Density Functional Theory ABSTRACT Ru(II)-dyads are a class of bioactive molecules of interest as anticancer agents obtained incorporating an organic chromophore in the light-absorbing metallic scaffold. A careful DFT and TDDFT investigation of the photophysical properties of a series of Ru(II)-polypiridyl dyads containing polythiophene chains of different lengths bound to a coordinating imidazo[4,5- f][1,10]phenantroline ligand, is herein reported. The modulation of the crucial chemical and