MECHANISM OF FLUORESCENCE QUENCHING OF PYRENE WITH PURINES IN POLAR MEDIA - FORMATION OF THE PYRENE TRIPLET-STATE VIA EXCIPLEX FORMATION

The kinetics and the mechanism of fluorescence quenching of pyrene by a number of purines, including their deprotonated anionic forms, were investigated in aqueous and acetonitrile solutions. In aqueous solution, the kinetics of the quenching was both dynamic and static, where there is appreciable formation of a ground-state complex between pyrene and purine. Only dynamic quenching was observed in acetonitrile. The quenching mechanism was shown to occur via exciplex formation due to a weak electron-transfer interaction from purines to pyrene. This leads to enhanced formation of the pyrene triplet state, as the pyrene triplet state was observed as the only transient product, and there was little formation of ionic species.