Study of the excited state dynamics to improve the optical limiting performance of tetra tolyl porphyrins
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The last two decades have witnessed an extensive research activity in the nonlinear optical, photophysical and photochemical properties of organic materials in general and metallo-porphyrins/related compounds in particular. The interest in metallo-porphyrins is many-fold. These molecules are found to have strong nonlinearity and fast response times, the desired criteria for making useful photonic devices. Previous theoretical and experimental studies have shown that there is an enhancement in the optical nonlinearity through population of the excited state1. Here, we look at the excited state contribution to nonlinear optical properties of tetra tolyl porphyrins as a function of the input intensity, the metal ions and the axial substituents. The aim of the present study has been to incorporate structural modifications to the porphyrins for application towards optical limiting. Optical limiting devices show linear absorbance at lower intensities and limit to a threshold transmittance at higher intensities due to reverse saturation of absorption. Such a nonlinear absorption can be achieved through excited state absorption (ESA) and two-photon absorption (TPA) in porphyrins. As the porphyrins posses very strong excited state absorption from both the triplet as well as the singlet states, they serve as the one of the best optical limiting materials. Study of the nonlinearity and elucidation of the dynamics associated with excited states of such molecules is therefore important from a fundamental as well as technological point of view.
KeywordsNonlinear Absorption Excited State Absorption Lower Excited State High Excited State Excited State Dynamic
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- K.M. Kadish, Q.Y.Y. Xu, B.G. Maiya, J.-M, Barbe, R. Guilard, J. Chem. Soc. Dalton Trans., 1531, 1989Google Scholar