Theoretical studies on hyperpolarizabilities and UV-vis-IR spectra of a diamminecobalt(III) tetripeptide transition-metal complex

The second-order polarizabilities and the UV-vis-IR spectra of a transition-metal complex Co(NH3)2(L-ala–gly–gly) have been studied by using the MP2 and TDHF methods. The complex has a maximum β component in the direction from the N(alanyl) group to the N(glycyl) groups. A transparent optical spectrum region from 0.55 to 5.5 µm was found, which offers potential applications as an optical material. The alkyl substitution of the glycyl group only slightly affected the β value and retained the IR transparent region but may cause the molecules to have a favorite packing fashion in the bulk crystal that leads to larger second-order nonlinear optical coefficients.