PHOTODIMERIZATION OF HETEROARYLENE-VINYLENES

Various furanic and thiophenic compounds bearing conjugated structures , based on the bridging of heterocycles with alkenyl moieties, were ex cited in the near-UV in the solid state and in solution. E-Z isomeriza tion, leading to thermodynamic composition, was the dominant photochem ical pathway in dilute solution, whereas [pi 2 + pi 2] cyclodimerizati on through external unsaturation occurred in concentrated media and, m ore efficiently, with crystalline morphologies. Compounds containing t wo independent chromophores dimerized giving the corresponding cycloph ane-type macrocycles. (C) 1997 Elsevier Science S.A.