Thioethyl Porphyrazines: Attractive Chromophores for Second-Order Nonlinear Optics and DSSCs

The first study on the second-order NLO properties of unconventional push-pull systems constituted by asymmetrically monoaryl-substituted thioalkyl porphyrazines, carried out by EFISH measurements and DFT calculations, is here reported. The results obtained show that the porphyrazine macrocycle behaves as a better electron donor and acceptor with respect to structurally similar porphyrin and phthalocyanine tetrapyrroles. Noteworthy, the highest quadratic hyperpolarizability (beta(1907)) values are displayed by the pyrene-substituted thioalkyl porphyrazines, both as free-base and as Pd-II complex, without the presence of either electron-withdrawing or electron-donating groups. In these cases, the pyrene moiety behaves as an electron-donating group, giving rise to charge transfer HOMO-LUMO electronic transitions. These outcomes show, for the first time, the great potential of the thioalkyl porphyrazine macrocycles for second-order NLO applications. Moreover, the hydroxyphenyl-substituted porphyrazine 2 dye has been also tested as a sensitizer in a TiO2-DSSC, representing the second example reported so far of a DSSC with thioalkyl porphyrazines.