Effect of molecular structure on optical second-harmonic generation from organic crystals

Optical second-harmonic generation coefficients have been measured for several organic molecular crystals. Variations in coefficients for related compounds can be correlated with differences in molecular structure. Highly polarizable aromatic molecules with substituent groups arranged to produce a large static polarization are relatively efficient non-linear optical materials. Acentric alternant hydrocarbons have low coefficients, but if the alternancy property is broken down by substitution they behave normally. A method is described which will permit rapid evaluation of some non-linear coefficients for low-melting materials.