Non-linear optical properties of organic molecules. Part 3. Effect of substituents on the calculated hyperpolarisability of monosubstituted benzenes

Abstract

The hyperpolarisabilites of a range of substituted benzenes have been calculated using a modified CNDO/2-Cl method. The values obtained have been rationalised in terms of ground- and excited-state π-charges at the aromatic ring. It is shown that the effect of electron donors and attractors is generally enhanced relative to their behaviour in the corresponding ground state. Of the substituents studied, the NMe₂ group is calculated to be the most powerful electron-donating group and that the CHO, NO_2′ and NO groups are the most effective electron attractors.