Theoretical Exploration of Type I/Type II Dual Photoreactivity of Promising Ru(II) Dyads for PDT Approach

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]phenanthroline ligand is herein reported. The modulation of the crucial chemical and physical properties of the photosensitizer with increasing number of thiophene units has been accurately described by investigating the UV-vis spectra and type I and type II photoreactions, also including spin orbit coupling values (SOC). Results show that the low-lying (IL)-I-3 states afforded as the number of thiophene ligands increases (n = 3, 4) are energetically high enough to ensure singlet oxygen production and can be also involved in electron transfer reaction, showing a dual type I/type II photeoreactivity.