BRIDGE EFFECT IN CHARGE-TRANSFER ABSORPTION-BANDS - PARASUBSTITUTED BENZYLIDENEACETONES

The electronic absorption charge transfer bands in a series of para-su bstituted 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 pi-conduction channel. Absorption band s assignment of the pi-pi electronic transitions in the near ultravio let spectral region is carry out from an experimental and theoretical point of view. The photo-induced charge transfer spectral bands in the se aromatic compounds follow the same spectral pattern than the para-s ubstituted benzaldehydes and acetophenones and the electronic transiti on takes place in the pi,pi((1)L(a)) excited state. However, our semi empirical M.O. calculations show that this charge transfer process inv olve the electron-acceptor carbonyl group and the olefinic bond bridge as a second electron-acceptor group.