Laser photolytic studies on sensitizers for negative photoresists: 4,4′-diazido-3,3′-dimethoxybiphenyl in poly(methyl methacrylate) films
The time evolution of the transient absorption spectra of 4,4′-diazido-3,3′-dimethoxybiphenyl (DADMB)(N3—R—N3), a sensitizers for negative photoresists, under laser irradiation with low and high fluences has been investigated in poly(methyl methacrylate)(PMMA) films and in cyclohexane solution. The spectra were measured in the time region 20 ns–1200 s. The results from a DADMB–cyclohexane solution containing diethylamine indicated that the triplet azido nitrene (N3—R—N:) was predominantly generated even at room temperature, not didehydroazepine derivatives. The formation of the triplet azido nitrene in solution and in PMMA films was complete within the duration of the laser pulse. The triplet azido nitrene underwent dimerization in solution within 1 ms, producing an azo compound (N3—R—NN—R—N3). In contrast, a reaction related to the formation of azide nitrene in PMMA films continued up to 1200s. Laser irradiation with a high fluence gave the dinitrene (:N—R—N:). The dinitrene in solution underwent dimerization and/or further polymerization. The results for PMMA films heavily doped with DADMB suggested that DADMB molecules form aggregates in PMMA films: A photoreaction with a high fluence was complete within 300 s.