“…Conjugated polymers have large polarizabilities attributed to the delocalized nature of electronic excitations. Numerous experimental and theoreticalstudies have forged a pretty good understanding of their electronic and optical characteristics. , Pioneering theoretical investigations of NLO properties of polymers using solid-state physical concepts have been carried out by André, Champagne, and co-workers − These investigations utilized the sum over states 273 and the polarization propagator technique. , A similar study has been done by using a variational method for the time-dependent wave function. , Ab initio approach combined CPHF method has been applied to polyene oligomers of moderate sizes, , extrapolated to the infinite systems using the periodic boundary conditions, , and extended into finite frequency off-resonant regime. − It has been shown that vibrational contributions to the polarizability may be as important as their electronic counterparts. − These nuclear effects arise from geometry deformations induced by the external field π-electron delocalization and polymer nonrigid energy potential surface strongly enhances the vibrational contribution.…”