Effects of room temperature ionic liquids on fluorescence properties of bisphenol A in β-cyclodextrin

Abstract

Bisphenol A can form 1:1 supramolecular inclusion complexes with β-cyclodextrin, resulting in a prominent increase in fluorescence intensity. When room temperature ionic liquids (RTILs) were added to the bisphenol A-β-cyclodextrin system, the fluorescence intensity of bisphenol A-β-cyclodextrin markedly decreased, suggesting a fluorescence-quenching effect of RTILs on the inclusion complex. The longer the carbon chain length of RTILs, the weaker the fluorescence intensity of bisphenol A-β-cyclodextrin. However, there were no significant differences in Ksv values of bisphenol A-β-cyclodextrin among RTILs with three different anions (BF4−, PF6− and Cl−). The ΔF1=Fbisphenol A-β-cyclodextrin−Fbisphenol A-β-cyclodextrin-RTIL was about 3-fold larger than ΔF2=Fbisphenol A−Fbisphenol A-RTIL at 0.01mM of RTILs, demonstrating a significant sensitizing effect of β-cyclodextrin on the bisphenol A-RTIL quenching system. The ΔF1 values gradually increased with increasing RTIL concentration. Under optimum conditions, the linear regression equation was determined to be: ΔF=19.87+10.59c (mM), and the linear range was 1.0×10−3–1.0×10−1mM. The detection limit (S/N=3) was 9.6×10−5mM and RSD was 1.2% (n=5, c=3×10−3mM). The quenching mode was concluded to be a static quenching mechanism based on assessment for Ksv of fluorescence intensity (>1.0×103Lmol−1) and τ0/τ1 (1.014–1.066, close to 1) for fluorescence lifetime.