Two-photon absorption properties of substituted porphyrins

The two-photon absorption (TPA) properties of two newly synthesized substituted porphyrins: 5,10,15,20-tetra-(4-pyrrolidinylphenyl)porphyrin (1) and 5,10,15,20-tetra-(4-diphenyl-amino-benzoic acid phenyl) porphyrin ester (3) were measured by the femtosecond Z-scan technique at 800 nm Ti: sapphire laser and by direct nonlinear optical transmission (NLT) using nanosecond Nd: YAG laser. The substituent effects, pumped wavelength and the environment upon the molecular TPA cross-section were investigated. It is found that the TPA cross-section for 3 is enhanced under excitation of 800 nm, relative to its precursor, 5,10,15,20-tetra(4-hydroxyphenyl) porphyrin (2), due to the former possessing extension conjugation of "D-A-core-A-D" molecular architecture. Also sample 3 obtained an increased TPA cross-section in rigid film relative to that in solution, suggesting that the enhancement is facilitated by the quasi-planar structure which allows direct interbranch conjugation throughout the molecule.