Charge‐Transfer Interactions in 4‐Donor 4′‐Acceptor Substituted 1,1‐Diphenylethenes

AbstractTwo 1,1‐diphenylethenes bearing either a 4‐dimethylamino or 4‐methoxy group as electron donor and a 4′‐cyano group as electron acceptor, as well as compounds containing only a donor or acceptor functionality, were synthesized. The observation of strong fluorescence solvatochromism (originating from a biradicaloid twisted intramolecular charge‐transfer state) of the donor‐acceptor compounds reveals that photoinduced charge separation through the cross‐conjugated 1,1‐diphenylethene spacer occurs. The presence of weak charge‐transfer absorption bands in the UV spectra reflects modest ground state donor‐acceptor coupling. These results show that charge transport through a branched conjugation path is possible. 1‐[4‐(Dimethylamino)phenyl]‐1‐phenylethene was found to fluoresce from two different states. In nonpolar solvents the source is a local aniline‐like state, whereas in polar solvents the fluorescence originates from a twisted intramolecular charge‐transfer state. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)