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

The photochemical reaction process of anthraquinone-2-sodium sulfonate (AQS) in the mixture of water (H₂O) and N-butylpyridinium tetrafluoroborate (BPyBF₄) 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 (V_IL) in BPyBF₄/H₂O mixtures. The absorbance at 510 nm increased gradually with increasing V_IL when 0< V_IL< 0.1. By contrast, the absorbance decreased gradually when V_IL>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 BPyBF₄ and H₂O are a pair of competitive reactions. We also concluded that the entire reaction processes slow down in the case of high BPyBF₄ concentrations.