Second-order hyperpolarizabilities of aromatic carboxylates without visible absorption

The second-order hyperpolarizabilities (I) of aromatic carboxylates were evaluated by the hyper Rayleigh scattering method at 1.064 I and semiempirical molecular orbital calculation. The I values of methyl methoxybenzo-ate and its dimer in methanol solution were measured to be 22 and 49 x 10^-30 esu, respectively, which are about 0.6 and 1.3 times that of p-nitroaniline. The calculation of I and dipole moment (I) of the methyl methoxybenzo-ate oligomers revealed an almost linear increase of these values with increasing number of repeating units up to trimers. Since the oligomers have a short cutoff wavelength of about 300 nm as well as large I and, these compounds are concluded to be promising chromophores for second-order nonlinear optics.