Photochemistry and photophysics of a polycyclic azoalkane: solvent and temperature effects

Abstract

Direct photochemical excitation of the polycyclic azoalkane 1 yields a mixture of (CH)₆ isomers as major products at room temperature and the 1,2-diaza-cyclooctatetraene 2 as the major product at - 78°C. The ratio of (CH)₆ isomers to 2 is strongly dependent on solvent. For example, at room temperature the ratio (CH)₆/2 is 92/8 in pentane and 38/62 in dimethyl sulfoxide. Triplet photosensitized excitation of 1 yields 2 as the major product. The triplet reaction is insensitive to temperature and solvent. These results are consistent with reaction of S₁(1) to yield predominately (CH)₆ isomers via a thermally activated nitrogen extrusion, whereas T₁(1) yields predominantly 2 via a temperature and solvent independent rearrangement. Quantitative measurement of photochemical and photoluminescence parameters reveals that the solvent effect on the product distribution in the direct photolysis of 1 is due to a combination of the influence of solvent on the rate of reaction from S₁ and the rate of intersystem crossing from S₁.