FURTHER-STUDIES ON THE POLARIZABILITIES AND HYPERPOLARIZABILITIES OF THE SUBSTITUTED POLYENES AND POLYPHENYLS

The polarizabilities and first and second hyperpolarizabilities of the all-trans donor-acceptor substituted polyenes and polyphenyls, (CH3)(2)N-(CH=CH-CH=CH)(n)-NO2 and (CH3)(2)N-(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 pi-electron configurations obtained from a group of six occupied and four unoccupied Hartree-Fock pi 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 pi-pi* 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.