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-corrected density-functional calculations are combined to study trans-1-(2-pyridyl)-2-(it-pyridyl)-ethylene, 2,4-DPE, a stilbenelike molecule. The interplay between experiments and computational theory backed by the large 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 inertia (-1.295 u Angstrom(2)). The large difference between the defects of inertia of 2,4-DPE and stilbene (approximate to-15 u Angstrom(2)) and further computer simulations suggest that the latter may warrant a reinvestigation. The effect of introducing a weakly binding N ... H interaction in the stilbene frame is discussed and a very simple model based on the ab initio calculations is found to rationalize the energetics and structural differences of the two conformers of 2,4-DPE. (C) 1997 American Institute of Physics.