Synthesis of axially substituted tetrapyrazinoporphyrazinato metal complexes for optical limiting and study of their photophysical properties.

The synthesis, characterization, and various photophysical properties of axially substituted tetrapyrazinotetraazaporphyrinatotitanium(IV) oxide (Pyz(4)TAPTiO) (1), tetrapyrazinotetraazaporphyrinatovanadium(IV) oxide (Pyz(4)TAPVO) (2), tetrapyrazinotetraazaporphyrinatozirconium(IV) dihydroxide [Pyz(4)TAPZr(OH)(2)] (3) are reported. Nonlinear optical (NLO) properties of Pyz(4)TAPs 1-3 have been evaluated at 532 nm with nanosecond pulses for optical limiting (OL). It is found that the introduction of nitrogen atoms in the condensed rings of the tetrapyrrolic macrocycles together with the presence of axial substituents lead to an improvement of the excited-state absorption properties in comparison to phthalocyanines (Pcs). In the linear optical regime Pyz(4)TAPs 1-3 display a blue shift (about 50-60 nm) of the main UV-vis absorption bands with respect to Pcs and exhibit orange-red fluorescence, which can be observed with the eye in the case of 1. Frontier electronic orbitals of a Pyz(4)TAP could be depicted from available experimental data and the results of density functional theory (DFT) calculations. In the solid state, Pyz(4)TAPTiO (1) displays photoconducting properties.