Optimization of the room-temperature phosphorescence of the 6-bromo-2-naphthol-alpha-cyclodextrin system in aqueous solution

The influence of different factors on the room-temperature phosphorescence (RTP) emission from the inclusion complex between alpha-cyclodextrin (alpha-CD) and 6-bromo-2-naphthol (BN) was analyzed. Although RTP signals are detected even in aerated solutions, an efficient enhancement of the phosphorescence emission (about 13 times) is obtained when the solutions of the complex are deaerated with nitrogen bubbling, while quenching is produced when sodium sulfite is used for deoxygenation. Association constants of the 1:1 and 2:1 alpha-CD-BN complexes have been evaluated by molecular absorption and fluorimetric methods. Exciting at 287 nm, the RTP phosphorescence emission showed two maxima located at 500 and 535 nm and a shoulder at 577 nm. The RTP emission increases with the irradiation time of the sample by the xenon lamp of the fluorimeter, until it achieves a constant value after around 10 min of irradiation. The addition of organic molecules such as alcohols and bromoalcohols as a third component of the system produces an enhancement of the RTP emission smaller than that obtained in the absence of them. The calibration graph for BN was linear for the range of concentrations between 0.4 and 2.0 mug ml(-1) with a detection limit of 0.26 mug ml(-1), with relative standard deviation (RSD) (n=6) of 4%, for 1.6 mug ml(-1). The solution was transparent, and there was no precipitation.