STILBENOID MOLECULES - AN EXPERIMENTAL AND THEORETICAL-STUDY OF TRANS-1-(2-PYRIDYL)-2-(4-PYRIDYL)-ETHYLENE AND THE PARENT MOLECULE

Free-jet absorption millimeter-wave spectroscopy and gradient-correcte d density-functional calculations are combined to study trans-1-(2-pyr idyl)-2-(it-pyridyl)-ethylene, 2,4-DPE, a stilbenelike molecule. The i nterplay between experiments and computational theory backed by the la rge amount of data and modeling already available for stilbene allows us to establish the parameters of the two-dimensional potential of the pyridyl torsions which well reproduce the experimental defect of iner tia (-1.295 u Angstrom(2)). The large difference between the defects o f inertia of 2,4-DPE and stilbene (approximate to-15 u Angstrom(2)) an d further computer simulations suggest that the latter may warrant a r einvestigation. The effect of introducing a weakly binding N ... H int eraction in the stilbene frame is discussed and a very simple model ba sed on the ab initio calculations is found to rationalize the energeti cs and structural differences of the two conformers of 2,4-DPE. (C) 19 97 American Institute of Physics.