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 (β) 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-П-Y systems we find group polarizabilities in the order N(Et)2 > NBr2 > N(Me)2 > NHMe > PH2 > NHNH2 > SH > Br ∼ BH2 ∼ CHO ∼ NHOH ∼ NH2 > CN ∼ CH3 ∼ Cl > NF2 ∼ OCH3 ∼ OH > H ∼ F. The study reveals inverse relationship between the Egap and first static hyperpolarizabilities. Compounds with the N(Et)2, NHNH2, N(Me)2, NHMe, NHOH, NH2 and OH end parts have large β values. A poor agreement results between the Ab initio and the AM1 values which give a correlation coefficient of 0.88.