A Novel Photometric Method for the Determination of Photoacid Generation Efficiencies Using Benzothiazole and Xanthene Dyes as Acid Sensors

We report here on a new photometric method for acid quantification in nonaqueous media which has been developed to facilitate quantification for photoacid generators (PAGs) employed in resist compositions for microlithography, but may find application in other fields. The method employs laser excitation of the PAG and is based on the acid-induced bathochromic shift in the absorption spectra of a selected organic dye such as rhodamine B (RB), fluorescein (Fl), coumarin 6 (C6), and 2-[4-(3,4-dimethoxyphenyl)-1,3-butadienyl]benzothiazole (DB). The differences in signal intensity of the protonated form of the sensor are used to evaluate the differences in acid generation efficiencies of the PAGs by relative actinometry. To test this methodology, we have determined the photoacid generation efficiencies of 2-methyl- (1), 2-(2‘-furyl ethylidene)- (2), and 2-(4‘-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine (3) in acetonitrile by laser flash photolysis, using direct 308 nm laser excitation for 2 and 3 an...