Synthesis and Reactivity of 3-Diazo-4-oxocoumarins for Photolithographic Applications

3-Diazo-4-oxocoumarins absorb in the deep ultraviolet (DUV) and upon photolysis undergo a Wolff rearrangement in aqueous environments to afford carboxylic acid photoproducts that are transparent in the DUV. Because this photochemical reaction transforms a base insoluble chromophore into a base soluble one, it may be exploited for the design of photolithographic materials. Examples of 5-, 6-, and 7-substituted 3-diazo-4-oxocoumarins have been synthesized and the reactivity of the corresponding photogenerated ketenes has been studied. For most chromophores, the rate of ketene hydrolysis was found to correlate with the calculated charge on the ketenyl carbon. 3-Diazo-4-oxocoumarins bearing electron-donating substituents in these positions demonstrate the lowest reactivity and therefore show the most promise for lithographic materials.