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The mechanisms of the photochemical rearrangements of isoxazoles, 2-cyanophenol, pyrazoles, and anthranilonitriles have been investigated using low-temperature techniques. Isonitrile 14 was detected by ir (2130 cm-1) and uv in the photoconversion of indoxazene (2) to benzoxazole (3). Compound 14 was further identified by independent synthesis and hydrolysis to the formanilide 15 in acid. 2-Cyanophenol (1) is also formed on photolysis of 2; however, no intermediate could be detected in this conversion. Quenching and sensitization studies suggest that the formation of 3 proceeds from the singlet and 1 from the triplet excited states. The solvent dependence of the reaction suggests that 3 is formed from an initial , * excitation and 1 is formed from an n,ir* excitation. The photoconversion of 1 to 3 may also proceed by 14 as shown by the uv spectrum of the reaction mixture after irradiation at -77°. No intermediates were identified in the photochemical conversion of indazoles to benzimidazoles and anthranilonitriles using the above techniques. Emission measurements of the singlet and triplet energies of all the compounds used in this study are reported.

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The development of tunable organic dye lasers is proving to be a significant advancement in the field of photochemistry.1 •2 A major difficulty of organic dye laser systems is that quenching of stimulated emission may occur when the singlet state undergoes intersystem crossing to a triplet state. The triplet state of dye molecules is