The Nonlinear Optical Properties of Ferrocene-containing Metalloporphyrins Toward the Pico-second Laser

Background: The nonlinear optical properties of ferrocene-containing metalloporphyrins toward pico-second laser were studied using calculational and experimental methods, and the relationship between their structures and nonlinear absorption properties were discussed. Aims: The metal ions introduced into the porphyrin rings intensively affect the nonlinear optical properties. Methods: The nonlinear optical properties and the relationship between the property and the structure of the synthesized ferrocene-containing metalloporphyrins are studied using the calculational method and the open-aperture Z-scan technology for pico-second laser. Results: The Z-scan results show that Co-P-Fc, Zn-P-Fc and Pd-P-Fc exhibit reverse saturable absorption characteristics toward the laser with 532 nm wavelength and 21 ps pulse width, and the nonlinear absorption coefficients (β) of them were 4.1, 3.2 and 1.3 cm/GW, respectively, when the incident laser fluency at the focal point of the lens is 29 mJ/cm². In addition, the values of β decrease with the increase of the incident laser fluency. These results indicate that the nonlinear absorption characteristics of Co-P-Fc, Zn-P-Fc and Pd-P-Fc are ascribed to the excited state absorption (ESA). However, Cu-PFc, Ni-P-Fc and P-Fc show saturated absorption characteristics toward the ps laser pulse. Conclusion: To elucidate the intrinsic factors that influence the nonlinear optical properties, the electronic distribution, flow of charge density during the transition from the ground state to the excited state, and the first-order hyperpolarizability values (β) are calculated using the time-dependent density functional theory (TD-DFT). The calculated results show that the molecular polarity and the change of the molecular polarity before and after the transition from HOMO to LUMO, which is dominated by the redox potentials of the introduced metal ions, are the most important factors that affect the nonlinear optical properties of the title compounds.