Laser Flash Photolysis Mechanism of Anthraquinone-2-Sodium Sulfonate in Pyridine Ionic Liquid/Water Mixed System

Abstract

The photochemical reaction process of anthraquinone-2-sodium sulfonate (AQS) in the mixture of water (H2O) and N-butylpyridinium tetrafluoroborate ([BPy][BF4]) was studied using the laser flash photolysis technique. Experimental results show that the excited triplet of AQS (3AQS*) could react rapidly with H2O and the transient absorption spectra greatly changed by increasing the volume fraction of the ionic liquid (VIL) in [BPy][BF4]/H2O mixtures. The absorbance at 510 nm increased gradually with increasing VIL when 0<VIL<0.1. By contrast, the absorbance decreased gradually when VIL>0.1. Otherwise, the absorbance of the band near 380 nm steadily increased. The apparent kinetic parameters of transient species B and 3AQS* are obtained approximately. 3AQS* abstracting hydrogen from [BPy]+ was also explored. It was deduced that the 350–420 nm band was the superposition of the peaks of 3AQS* and AQSH·. The two reactions of 3AQS* with [BPy][BF4] and H2O are a pair of competitive reactions. We also concluded that the entire reaction processes slow down in the case of high [BPy][BF4] concentrations.