Density Functional Theory of Second-order Nonlinear Optical Properties of a Series of Organic Dendrimer Molecules with an Imidazole Chromophore

Density functional theory(DFT) B3LYP/6-31G* method was employed to optimize the structures of a series of organic dendrimer molecules containing an imidazole chromophore and second-order nonlinear optical properties. Results show that the molecules possess A-pi-D-pi-A( A: acceptor, D: donor) structures, and the dipole moment of the ground state, the polarizability, and the second-order nonlinear optical(NLO) coefficient(beta) of the molecules increase with the increase of the length of conjugate bridge of the branched chain and the conjugation effect of the chromophore. The molecule with smaller energy gap of the frontier molecular orbital shows larger values of the second-order NLO coefficient beta(tot). The calculated electronic absorption spectra of the organic dendrimer molecules exhibit the most intensive excitations in the low-lying region 247.79-419. 87 nm, which are arisen from the charge transfers from HOMO to LUMO.