SYNTHESIS AND FLUORESCENCE OF A CONFIGURATIONALLY LOCKED Z-HEXATRIENE- 1,2-DIVINYLCYCLOPENTENE

The syntheses of the configurationally locked Z-hexatriene, 1,2-diviny lcyclopentene, and its terminally tetradeuterated isotopomer are descr ibed, and some photochemical and photophysical properties are reported . The trienes turn out to be photostable under oxygen-free conditions. In contrast to ''unlocked'' hexatrienes, both compounds fluoresce (ro om temperature, methanol). The fluorescence is structured and is the n early perfect mirror image of the absorption band, with a small Stokes shift. Therefore the emission might originate in the 1 1B1 state. Thi s is the first observation of fluorescence of simple hexatrienes in so lution. Apparently torsional motion around the central (originally dou ble) bond in the excited singlet state is an important radiationless d eactivation pathway in ''unlocked'' hexatrienes; if it is obstructed f luorescence becomes a passable deactivation pathway.