Steric Effect on the Molecular Hyperpolarizabilities of ￥a-Nitrostyrene Derivatives

摘要

The steric effect on the first order hyperpolarizability of the モ-nitrostyrene derivatives has been investigated by comparing the モ values and the dihedral angles between the aryl and nitroalkenyl groups. In general the モ value increased with the electron-donating ability of the substituent. The larger モ value for 3,4-dimethoxy-モ-nitrostyrene than that for p-methoxy-モ-nitrostyrene has been attributed to the lower charge transfer energy for the former. The most striking substituent effect was observed in the モ-methyl-モ-nitrostyrene derivatives. Thus the モ values for 3,4-dimethoxy- and p-methoxy derivatives of the latter decreased to near zero, probably because of the large distortion from planarity caused by the steric repulsion between the モ-methyl and the aryl groups. The larger モ value for p-dimethylamino-モ-methyl-モ -nitrostyrene has been interpreted with an increased electron-donating ability of the substituent and increased co-planarity.