The photophysical properties of three [M(phen)2dppz]2+ (M=Ru and Zn) derivatives for two-photon photodynamic therapy: Insights from theoretical investigations

Abstract

Density Function Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) are used to access the photophysical properties of [Ru(phen)2dppz]2+ and two designed [Zn(phen)2dppz]2+ derivatives for two-photon photodynamic therapy. The geometrical structures, electronic properties, one-photon and two photon absorption properties, spin-orbit matrix elements and energy gaps ΔES-T are calculated. The results demonstrate that the absorption wavelengths of these complexes are within the so-called phototherapeutic windows and have large two-photon absorption cross-sections to deeply permeate cancer tissue, especially for the [Zn(phen)2dppz]2+ derivatives with large π-conjugate surface. Furthermore, T1 energy of these three complexes is all higher than that required of generating singlet oxygen (0.98 eV). More importantly, the SOC constants and energy gap ΔES-T of these complexes indicating the ISC process can be effectively completed. Therefore, these three complexes all can be used as potential candidates in TP-PDT. In particular, the [Zn(phen)2dppz]2+ derivatives with large π-conjugate surface is proposed due to its low costing. Our study may help to rationalize the available experimental data and establish some guidelines for designing novel potential photosensitizers in two-photon photodynamic therapy.