Non-linear optical activity of azo dyes. Conformational effects on the quadratic hyperpolarisability of an azothiophene dye

Abstract

The molecular dipole moment and vector component of the hyperpolarisability of 4-[N,N-bis(2-acetoxyethyl)amino]phenyl-1-azo-2′ -(3′,5′-dinitrothiophene) have been calculated using a semi-empirical approach and the results compared with experimental measurements in solution. The calculated values are found to be highly dependent on the conformation of the bis(2-acetoxyethyl)amino group selected, though experimental results suggest that only certain conformations are preferred under the influence of an applied external electric field. The observed change in the sign of the hyperpolarisability in moving from an applied field to 0.925 to 1.17 eV is well reproduced by the calculations.