PHOTORACEMIZATION OF OPTICALLY-ACTIVE 1,1'-BINAPHTHYL DERIVATIVES - LIGHT-INITIATED CONVERSION OF CHOLESTERIC TO COMPENSATED NEMATIC LIQUID-CRYSTALS

The photochemistry and photophysics of a series of optically active 1,1'-binaphthyl derivatives was examined in fluid solution and in liquid crystalline media. The mechanism for the photoracemization of these compounds was examined by time-resolved laser spectroscopy. It was found that photoracemization occurs in the triplet state by atropisomerism. The efficiency of photoracemization is controlled primarily by the efficiency of intersystem crossing and the magnitude of the activation barrier for atropisomerism. The latter value is perturbable by the specific nature of the binaphthyl derivative. Attempts to partially photoresolve these binaphthyl derivatives in fluid solution and in liquid crystals were unsuccessful. However, their photoracemization induces a cholesteric to compensated nematic transition in doped liquid crystalline K-15.