Further studies on the polarizabilities and hyperpolarizabilities of the substituted polyenes and polyphenyls

Abstract

The polarizabilities and first and second hyperpolarizabilities of the all-trans donor–acceptor substituted polyenes and polyphenyls, (CH3)2N—(CHCH—CHCH)n—NO2 and (CH3)2N—(C6H4)n—NO2 have been calculated for values of n= 1 to 9 at a frequency corresponding to 0.65 eV, using a modified CNDOVSB method. A basis set including the 325 singly and doubly excited π-electron configurations obtained from a group of six occupied and four unoccupied Hartree–Fock π orbitals has been used and the polarizabilities and hyperpolarizabilities calculated by the correction vector method. The results are compared with earlier work based on an expansion in terms of a large set of singly excited configurations only. In the case of n= 3 for the polyenes and n= 2 for the polyphenyls calculations have been carried out with the complete set of π–π* configurations for each molecule, using both the correction vector method and the sum-over-states expansion. The results confirm the assessment of the quadratic non-linear optical potential of these compounds made in earlier work, although the absolute values of the first hyperpolarizabilities are somewhat reduced.