Photosensitive Monolayers. Photochemistry of Long-Chain Diazo and Azide Compounds at the Air-Water Interface

Article abstract of DOI:10.1021/ja00328a038

The photochemistry of a number of surface-active diazo and azide compounds was investigated in monolayers at the air-water boundary.Irradiation of long-chain α-diazo ketones with ultraviolet light leads to rapid loss of nitrogen.The resulting ketenes react with the subphase to generate carboxylic acids (photochemical Arndt-Eistert reaction) and dimerize to give β-lactones as side-products.A long-chain diester of 2-diazopropanedioic acid loses nitrogen and adds water, yielding the diester of 2-hydroxypropanedioic acid. α-Azido ketones split off nitrogen and the resulting isocyanates react with water (photoche mical Curtius reaction) and undergo further degradation to give complex product mixtures.These reactions lead to pronounced changes in the spreading behavior of the monolayers.Depending on functional group, chain length, substrate pH, and temperature it is possible to achieve changes in compressibility and collapse pressure, disappearance of expanded phases, collapse of monolayers to give oily films, or disappearance of monolayers by dissolution in the subphase.