1,2-Diphenylcycloalkenes: Electronic and Geometric Structures in the Gas Phase, Solution, and Solid State

Article abstract of DOI:10.1021/ja00222a001

The geometric and electronic structures of several 1,2-diphenylcycloalkenes have been investigated by ultraviolet photoelectron spectroscopy(UPS), optical spectroscopy, X-ray crystal analysis, and theoretical calculations.The 1,2-diphenylcycloalkenes can be viewed as model cis-stilbenes in which cis-trans isomerization is not possible or at least is strongly hindered.In contrast to the unsubstituted cycloalkenes and the monophenylcycloalkenes, the first ionization potential of the diphenylcycloalkenes increases with increasing ring size.Optical spectra show an increasing blue shift of the first absorption band and an increasing Stokes shift with increasing ring size.These results have been compared to model calculations and to X-ray crystal structural data which allow us to establish connections between the changes in geometry and changes in the electronic structure of these systems.These results can only by explained by an increasing loss of planarity (decreasing conjugation) as the ring size increases in the 1,2-diphenylcycloalkene series.