Effect of the nature of aryl and heteroaryl groups on the excited state properties of asymmetric 1,4-diarylbutadienes

The excited state properties of a series of asymmetric 1-Ar,4-phenylbutadie nes (Ar = naphthyl, phenanthryl, anthryl, pyrenyl, pyridyl and thienyl) hav e been investigated by stationary and pulsed techniques with the main aim o f assessing the effect of the nature and size of the Ar group on the photop hysical and photochemical behaviour. The comparison of the present results with those of previous studies on the corresponding 1,2-diarylethenes shows how the extension of the unsaturated chain affects the excited state prope rties and opens alternative adiabatic and "one photon-two bonds" isomerizat ion mechanisms. The role of the relative position of the L, and Lb states o f Ar with respect to the olefinic B, state on the photobehaviour is discuss ed. (C) 2001 Published by Elsevier Science B.V.