Non-linear optical properties of organic molecules. Part 20. Calculation of the structure, electronic properties and hyperpolarizabilities of donor–acceptor heterocycles containing sulfur, oxygen and nitrogen

Abstract

The structures of a donor–acceptor thiophene, furan, pyrrole, thiadiazole, oxadiazole and the three ring tautomers of the corresponding triazole, have been calculated using the ab initio 3-21 G basis set to give a reasonable correlation with crystallographic data where available. The non-linear optical properties of these structures have been assessed by calculating their molecular hyperpolarizabilities using a sum-over-states semiempirical approach. The results show that the 1,3,4-thiadiazole, 1,3,4-oxadiazole and 1,3,4-triazole, exhibit much larger dipole moment changes than the corresponding thiophene, furan and pyrrole on excitation, but their calculated hyperpolarizabilities are smaller mainly because of their smaller transition moments.