Hyperpolarizabilities of organic molecules: Ab initio time-dependent coupled perturbed Hartree - Fock - Roothaan studies of basic heterocyclic structures

The linear polarizability, α, the first hyperpolarizability, β, and the second hyperpolarizability, γ, of three different classes of basic heterocyclic organic structures have been calculated by the ab inio time-dependent coupled Hartree - Fock - Roothaan method using a 4-31G basis set augmented by diffuse p and d functions. For the α and γ coefficients, the calculated orders thiophene > pyrrole > furan for the five-membered rings; pyridine > pyrazole > s-triazine for the aromatic bases; and benzothiazole > oxazole for the fused ring systems show a qualitative relationship with the corresponding order in Δε(HOMO-LUMO) of the respective group of molecules. The β values do not appear to show a discernible trend. The dispersion of α(-ω;ω) and those of γ(-ω;0,0,ω), γ(-ω;ω,ω,-ω), γ(-ω;0,ω,ω), and γ(-3ω;ω,ω,ω) in the case of the five-membered rings are also reported.