Asymmetrization effects on structures and populations of the ground state of dipolar donor-acceptor-substituted molecular organic NLO materials

Asymmetric donor]acceptor-substituted p-conjugated systems with low dipole moments and structural components that favor parallel alignment of neighboring molecules are potential molecular organic materials with nonlinear optical properties for which near prefect dipole parallel alignment is possible. The asymmetrical 4-methoxysubstituted acetophenone azines with Ž . Ž . Ž . Ž . Ž . the substituents fluorine 1 , chlorine 2 , bromine 3 , cyano 4 , and nitro 5 in the 4-position have been studied in this context, and for 2 and 3 the dipole parallel alignment has indeed been accomplished in crystals of the pure material. In the present study, the effects of asymmetrization on the structure and the electronic structures of the ground states of 1]5 have been explored at the RHFr6-31G level. The properties of the optimized structures of the azines 1]5, a comparative analysis of asymmetrical and symmetrical azines, and natural population analyses, all show no significant evidence for conjugation over the azine bridge. The concept of azine spacers as ‘‘conjugation stoppers’’ is useful and the dipole moments of asymmetrical azines are relatively small. The analysis suggests that the charge transfer between the donor and acceptor contributes to the dipole moment much less than is generally assumed. Q 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1130]1140, 1998 Dedicated to Prof. N. L. Allinger Correspondence to: R. Glaser; e-mail: [email protected] Contractragent sponsors: Research Board of the University of Missouri, National Science Foundation, the State of New York; Advanced Research Projects Agency; National Center for Research Resources at the NIH; IBM Corporation; Corporate Research Institute ( ) Journal of Computational Chemistry, Vol. 19, No. 10, 1130]114