| Abstract
| - The multiphoton absorption properties of the tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazinato(monoacquo)-Mg(II) complex [Py8TPyzPzMg(H2O)] (1) are reported and interpreted. The nonlinear optical behavior of 1and the characterization of the excited states important for the nonlinear absorption process were studied atthe pump frequency of the second harmonic generation of a Nd:YAG laser in the nanosecond time regime.It was found that complex 1 shows a very good optical limiting performance at 532 nm, which derives fromtwo processes: (a) a reverse-saturable absorption process, which involves a triplet excited state at low intensities,and (b) a two-photon absorption process at higher intensities, which is due to the formation of the radicalmonoanion of 1, [Py8TPyzPzMg(H2O)]•-, during the photoreduction of the triplet state. The participation ofa monoanion in determining the overall nonlinear absorption behavior of 1 is found, for the first time, for atetrapyrrolic system. One can deduce that the involvement of the monoanion derives from the electron-withdrawing effect of the dipyridinopyrazino fragments externally attached to the porphyrazine core whichmake the reduced form of 1 easily accessible. These results suggest a modification of tetrapyrrolic systemswith new nonlinear absorption properties.
|
