Aromatic Monoazines as Fluorescent Sensors for Photoacid Generation in Thin Polymer Films

This paper reports a novel approach to monitor photoinduced acid generation in polymer films of the type used in microlithography. We have employed fluorescent acid-sensitive sensors to monitor the progress of photoacid generation in solution and in thin polymer films. We have studied the effect of p -toluenesulfonic acid on the spectral properties of 2-phenylpyridine, 2-phenylquinoline, and acridine in diglyme solution and in poly(methyl methacrylate) (PMMA) films using absorption and fluorescence spectroscopy. In both cases a bathochromic spectral shift and an increase in fluorescence quantum yield are observed upon protonation. In samples containing a photoacid generator, the acid production upon irradiation could be monitored by observing the increase in fluorescence intensity with proceeding irradiation time in both solution and PMMA films. This new acid-monitoring method may find application in the study of diffusional processes in polymer films.