Abstract
Phenyl benzoates and phenyl- trans-cyclohexane-1-carboxylates react to rearrangement and fragmentation products on UV irradiation (photo-Fries reaction). Quantum yields for the formation of o-hydroxyphenones via the photo-Fries reaction of rod-like liquid crystalline esters were measured as a function of temperature in different liquid crystalline ordered solvents as well as in neat mesophases of esters. The quantum yields of the o-photo-Fries product increase generally with temperature and are influenced by the ordered matrix of liquid crystals. They are lower in smectic than in nematic mesophases and these are lower than those in isotropic melt or in solution. The activation energies for the ortho product formation are in paraffin 5.1, in the isotropic melt 5.2, in the nematic phase 24.6, and in the smectic mesophases 48.4 kJ mol −1. The density or better the packing of molecules in mesophases influences the quantum yield of the o-photo-Fries product formation in the photolysis of rod-like molecules.
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