NONLINEAR-OPTICAL ACTIVITY OF AZO DYES - CONFORMATIONAL EFFECTS ON THE QUADRATIC HYPERPOLARIZABILITY OF AN AZOTHIOPHENE DYE

The molecular dipole moment and vector component of the hyperpolarisab ility of 4-[N,N-bis(2-acetoxyethyl)amino]phenyl- 1-azo-2'-(3',5'-dinit rothiophene) have been calculated using a semi-empirical approach and the results compared with experimental measurements in solution, The c alculated values are found to be highly dependent on the conformation of the bis(2-acetoxyethyl)amino group selected, though experimental re sults suggest that only certain conformations are preferred under the influence of an applied external electric field, The observed change i n the sign of the hyperpolarisability in moving from an applied held t o 0.925 to 1.17 eV is well reproduced by the calculations.