Semi empirical and Ab initio methods for calculation of polarizability (α) and the hyperpolarizability (β) of substituted polyacetylene chain

We report accurate Ab initio studies of dipole polarizabilities and the first static hyperpolarizabilities (beta) of polyacetylene with a number of substituents at the end part of the linear system. Geometries of all molecules were optimized at the Hartree-Fock level with the 6-311G++(d,p) basis set. The results indicate that for the NO2-Pi-Y systems we find group polarizabilities in the order N(Et)(2) > NBr2 > N(Me)(2) > NHMe > PH2 > NHNH2 > SH > Br similar to BH2 similar to CHO similar to NHOH similar to NH2 > CN similar to CH3 similar to Cl > NF2 similar to OCH3 similar to OH > H similar to F. The study reveals inverse relationship between the E-gap and first static hyperpolarizabilities. Compounds with the N(Et)(2), NHNH2, N(Me)(2), NHMe, NHOH, NH2 and OH end parts have large beta values. A poor agreement results between the Ab initio and the AM1 values which give a correlation coefficient of 0.88. (C) 2012 Production and hosting by Elsevier B.V. on behalf of King Saud University.