Bridge Effect in Charge Transfer Absorption Bands. Para-substituted Benzylideneacetones

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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 substkuent 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.