The nonlinear absorption of tetraphenylporphyrin(TPP),copper tetraphenylporphyrin (CuTPP),zinc tetraphenylporphyrin(ZnTPP) and nickel tetraphenylporphyrin (NiTPP) in chloroform and pyridine at 532 nm is studied by using open aperture Z-scan.A theoretical analysis has been carried out to simulate ground state absorption cross-section, riplet state absorption cross-section and intersystem crossing time of the four samples by using five-level model.The change of solvent from chloroform to pyridine lead to a re...