Laser Flash Photolysis Study of Two Aromatic N-Oxyimidosulfonate Photoacid Generators

In this paper we study the photophysical and photochemical behavior of two aromatic N -oxyimidosulfonate photoacid generators (PAGs), N -trifluoromethylsulfonyloxy-phthalimide (PIT) and N -trifluoromethylsulfonyloxy-1,8-naphthalimide (NIT), by means of absorption and emission stationary techniques and nanosecond and picosecond laser flash photolysis. Triplet states have been detected for both compounds; lifetimes of 12 μs and 43 μs (acetonitrile solution) and 2 μs and 28 μs, (benzene solution), were measured for PIT and NIT, respectively. Photoacid generation quantum yields have also been measured (Φ = 0.28 in acetonitrile, Φ = 0.21 in benzene for PIT; Φ = 0.17 in acetonitrile, Φ = 0.09 in benzene for NIT), using Rhodamine B Base as an acid sensor and 2-methyl-4,6-bis(trichloromethyl)-1,3,5-triazine as a suitable actinometer with 308-nm laser excitation. Evidence that photoacid generation occurs through an ionic mechanism from the singlet state was obtained.