Non-linear optical properties of organic molecules. Part 8. Dipole moments and hyperpolarisabilities of some substituted azulenes and aza-azulenes

Abstract

Semi-empirical and ab initio calculations are reported on the dipole moments and hyperpolarisabilities of azulenes and aza-azulenes based on structures derived either from crystallographic data or from STO-3G optimisations. A comparison between calculated and experimental dipole moments suggest that the amino group in 2-aminoazulene is tetrahedral while that in the corresponding 2-acetamido derivative is trigonal. The results show that the dipole moment of the azulene ring can be adjusted to favour possible non-centrosymmetric crystal forms by inserting nitrogen into the ring in place of carbon without markedly changing the magnitude of the large calculated hyperpolarisability.