Spectrochemical evaluation of pyridinium chloride as a possible selective fluorescence quenching agent of polycyclic aromatic hydrocarbons in water and neat acetonitrile

Pyridinium chloride (PC) is examined as a selective, fluorescence quenching agent for alternant as opposed to nonalternant polycyclic aromatic hydroca rbons (PAHs) in two polar solvents - water and acetonitrile. Nine alternant and 13 nonalternant PAI-Is were dissolved in water and acetonitrile and a total of 0.2 M of pyridinium chloride was added. The resulting change in fl uorescence intensity was observed and reported as the Stern-Volmer quenchin g constant. Results show that PC is a selective quencher in both polar solv ents. It selectively quenches the fluorescence emission intensity of altern ant PAHs while leaving the nonalternant PAH fluorescence emission virtually unchanged. These results agree with the selective quenching behavior seen for PC surfactant analogs, cetylpyridinium chloride (CPC) and dodecylpyridi nium chloride (DDPC). Furthermore, these results illustrate that the presen ce of a surfactant or micelle is not a requirement for selective quenching. The selective quencher PC is applicable to situations where a surfactant i s not desirable or soluble. (C) 2000 Elsevier Science B.V. All rights reser ved.