SOLUBILIZATION AND PHOTOREACTIVITY OF E-ETHYL CINNAMATE IN SMECTIC-B MESOPHASES .7. PHOTOREACTIONS IN LIQUID-CRYSTALS

The relative quantum yields of (2 + 2) photocycloaddition for E-ethyl 4-methoxycinnamate 1 have been estimated in smectic and nematic phases as well as in isotropic melts of trans, trans-4'-n-butyl- and trans, trans-4'-ethylbicyclohexyl-4-carbonitrile (CCH-4 and CCH-2). The quantum yield is significantly higher in smectic B phases compared to the values in the isotropic and nematic range. The existence of a second smectic phase, S2, of CCH-4 has been shown. The photoreaction does not occur in this mesophase. The solubilization behaviour of deuteriated E-ethyl 4-methoxycinnamate has been studied by means of H-2, H-1, and C-13 NMR as well as DSC and thermal microscopy. The cinnamate has a very low solubility in SB phases (< 0.5 wt %) in contrast to the S2 and nematic phases. The results indicate that phase separation occurs to cinnamate-rich nematic or isotropic regions below the bulk smectic B-nematic transition temperature. Thus, the high quantum yields are due to compartmentalization of the cinnamate in nematic or isotropic spheres of the biphasic smectic B-nematic or smectic B-isotropic systems.