One- and two-photon activity of diketopyrrolopyrrole-Zn-porphyrin conjugates: linear and quadratic density functional response theory applied to model systems

Abstract

The present work, based on linear and quadratic response theories within the framework of time-dependent density functional theory, is devoted to the solvent phase one- and two-photon (TP) absorption properties of four dikeotpyrrolopyrrole (DPP)-substituted Zn-porphyrin complexes and their possible application as photosensitizers in photodynamic cancer therapy. We have also compared our results, wherever possible, with the available experimental data. Our analysis decisively confirms that although the reference compound has very low TP activity the other substituted complexes show a very large TP activity in the tissue penetration region, activity that gradually increases with the number of DPP ligands. We have explained the results by extensive analyses of the orbital excitations as well as the different TP tensor elements involved in the TP absorption process.