Nonlinear light absorption in meso-substituted tetrabenzoporphyrin and tetraarylporphyrin solutions Original Research Article

The characterization of fluence-dependent nonlinear absorption and the excited state absorption cross-sections of the zinc complexes of tetrabenzoporphyrin with meso-substituents of phenyl and thienyl (Ia and Ib), and the zinc and lead complexes of porphyrin with meso-substituent of 3,4,5-trimethoxyphenyl (IIa and IIb) are determined with the Z-scan method. The results from Ia and Ib are comparable with the literature report. The lead porphyrin of IIb gives the largest triplet excited state absorption cross-section (σexT=3.3×10−16 cm2) among these compounds, and shows very strong optical limiting power as a result. Whereas we obtain the smallest σexT=2.5×10−17 cm2 for the zinc porphyrin bearing four electron withdrawing groups of benzoquinone (compound III), which exhibits unique linear absorption property at 532 nm. This result could be due to the rapid decay of its lowest triplet state to yield both long-lived triplet biradicals and S0 states.