First-order hyperpolarizabilities (beta) of a series of p-substituted
cinnamic acids have been measured using the hyper-Rayleigh scattering
technique and compared with those of p-substituted benzoic acids. beta
in these acids increases as a function of the donor strength. It incr
eases twice with the increase in the effective chain length. Semi-empi
rical calculations also support this enhancement. Solvents effects are
dealt with at the ab initio level within the self-consistent reaction
field approach.