Conformations and barriers to internal rotation in trans-diarylethylenes: Theoretical investigation using a new INDO-type method (C-INDO)

C-INDO, a new INDO-based technique specially devised for conformational studies of conjugated systems, is used to investigate conformational equilibria in ground state trans-diarylethylenes, as revealed by a number of emission spectroscopic observations (both steady-state and time resolved). Conformations, ΔE and barriers to internal rotation are provided for all the possible rotamers of 1-StN (1-styrilnaphthalene), 2-StN, 2,2′-DNE (2,2′-dinaphthylethylene) and 1,2′-DNE. Energetic parameters are used to predict the relative abundances of the distinct rotameric species at equilibrium as well as to estimate the rate at which equilibria are established (at different T). The results prove to be a consistent basis on which experimentally observed behaviour can be rationalized.