THEORETICAL-STUDIES OF THE ELECTRONIC-STRUCTURE, CONFORMATIONS, SPECTRA AND HYPERPOLARIZABILITIES OF SQUARATES AND RELATED MOLECULES

Calculations are reported on the structure and conformational energies of substituted deltates, squarates, croconates and rhodizonates at th e ab initio 3-21G level. The calculated hyperpolarisabilities of these structures using both the coupled Hartree-Fock and sum-over-states me thods increase with increasing ring size. Both dimethyl croconate and dimethyl rhodizonate give values which are comparable to N,N-dimethyl- 4-nitroaniline. These molecules are predicted to absorb in the ultravi olet region of the spectrum and have potential applications as second harmonic generators.