The effect of metal-to-ligand charge transfer on linear and nonlinear optical properties of hexaphyrin and metallo-hexaphyrins

Charge transfer from metal to ligand has implications in various fields of chemistry, physics and biology. The manipulation of spin properties would be necessary for controlling charge transfer in spintronics and biological applications. Upon binding to the metal atoms (Ni, Cu, Au, etc.), the spin properties would be modulated in organic conjugated molecules of less intrinsic spin–orbit coupling (SOC) due to SOC coming from the heavy elements. Emission spectra calculation is necessary to validate them as suitable fluorescence quenchers. The nonlinear optical properties like first-order hyperpolarisability <i>β</i> and second-order hyperpolarisability <i>γ</i> calculations are important to find out their relation between fluorescence quenching and higher order nonlinear optical (NLO) properties. From the second-order NLO properties, we computed degenerate four-wave mixing (<i>DFWM</i>) component (γ(2)(−ω;ω,ω,−ω)) and finally quadratic nonlinear refractive indices of the expanded porphyrins (EPs). How the linear and nonlinear optical properties are dependent on the SOC coming from the heavy materials (Ni, Cu, Au), and charge transfer process is the most interesting question to be addressed for their potential uses for various optoelectronic and spintronic applications.