Theoretical studies on the non-linear optical properties of some organic molecules: effect of #pi#-#sigma#-#pi# through-bond coupling on the first hyperpolarisability

摘要

First hyperpolarisabilities (#beta#) are calculated by means of semi-empirical molecular orbital methods for a series of organic molecules containing a #pi#-electron donor and a #pi#-electron acceptor separated by a saturated C-C #sigma# bond. The #pi# orbitals of the donor and the acceptor interact through the #sigma# skeleton (#pi#-#sigma#-#pi# through-bond coupling), giving rise to intramolecular charger transfer in the excited states. In the case of zwitterions (D~--#pi#-C-C-#pi#-A~+) very large hyperpolarisabilities and dipole moments are obtained. These studies suggest that this structural motif may have potential applications in the development of non-linear optical materials.