The application of time resolved EPR to the study of photoreactive molecules in solid and liquid crystalline environments

The use of transient EPR spectroscopy for the study of photoreactions in solid and liquid crystalline is demonstrated. The method is applied to an intramolecular photoreaction in 2-(4-methylpentyl)-7-nonanoylfluorene (MPNOF) and to an intermolecular photoreaction in 4-cyano-4′-octylbiphenyl (8CB) doped with phenazine. It is shown that both MPNOF and phenazine undergo photoreactions via their first excited triplet state. Orientational ordering in the solid and liquid crystalline phase is studied via the excited triplet powder spectrum. Spectra of precursor and products can be identified and separated by their kinetics. The possible nature of the products of reaction is discussed.