Bridge effect in charge transfer absorption bands. para-substituted benzylideneacetones

Abstract

The electronic absorption charge transfer bands in a series of para-substituted benzalketones are analyzed in order to stablish the role of the electron-donor substituent as well as the electronic properties of the molecular structure of the π-conduction channel. Absorption bands assignment of the π-π* electronic transitions in the near ultraviolet spectral region is carry out from an experimental and theoretical point of view. The photo-induced charge transfer spectral bands in these aromatic compounds follow the same spectral pattern than the para-substituted benzaldehydes and acetophenones and the electronic transition takes place in the π,π*(1La) excited state However, our semiempirical M.O calculations show that this charge transfer process involve the electron-acceptor carbonyl group and the olefinic bond bridge as a second electron-acceptor group.