Organic species with short cutoff wavelength and large second-order hyperpolarizability

In order to find short cutoff and large β materials for second-order nonlinear optics, a series of substituted aromatic carboxylate anions and esters were investigated by semiempirical molecular orbital calculation. Methyl benzoates with a weak donor or benzoate anions with a weak acceptor at para-position were found to satisfy those conditions. Among them, optical properties of methyl 4-methoxybenzoate and its oligomers were studied by both calculation and experiment. The μβ values of oligomers consisting of N monomeric units were found to become N-times larger than the sum of N isolated monomers, though the absorption cutoff of oligomers stays almost the same as that of methyl 4-methoxybenzoate.