AB-INITIO STUDIES OF THE DIPOLE POLARIZABILITIES OF CONJUGATED MOLECULES .4. THE DIPOLE POLARIZABILITY AND 1ST HYPERPOLARIZABILITY OF O-BENZYNE AND RELATED MOLECULES

We report ab initio SCF and Moller-Plesset MP2 calculations of the static dipole polarizability and SCF calculations of the first hyperpolarizability tensors of o-benzyne. The standard STO/6-31G basis set was augmented with s and p diffuse functions and multiple d polarization functions on the carbon atoms. Further p functions were also added on the hydrogen atomic centres. We compare the results for this molecule with those for ethyne, allene and s-cis-butadiene, for which we also report new polarizability tensor calculations. Comparison is made with experiment where possible. Using the largest basis set STO/6-31 + G(3d,3p) at the SCF level of theory, the alpha tensor components for o-benzyne were alpha(xx) = 41.80 u, alpha(yy) = 70.37 u and alpha(zz) = 82.8 u. The corresponding components of beta were 146.2, 36.3 and 9.7 u respectively. The MP2 procedure gives negligible improvements on the SCF average dipole polarizability predictions by using the STO/6-31 + G(d,p) basis set. We show that o-benzyne should be considered as a potential reagent for the design and synthesis of new non-linear optical materials. Our results could also be useful for the identification of this transient molecule in non-linear optical experiments.