Fluorescence Intensities and Lifetimes of Aromatic Hydrocarbons in Cyclohexane Solution: Evidence of Contact Charge-Transfer Interactions with Oxygen

The fluorescence lifetimes and intensities of naphthalene, phenanthrene, chrysene, and pyrene were measured as a function of oxygen concentration in cyclohexane solution. Stern-Volmer plots of intensities and lifetimes versus oxygen concentrations revealed smaller Stern-Volmer quenching coefficients for lifetimes than for intensities. Analysis of the data in terms of static quenching models suggests that the Stern-Volmer slope differences result from a charge-transfer interaction between the aromatic and oxygen molecules in the cases of naphthalene and pyrene. A method of estimating dissolved oxygen concentration using the cyclohexane-oxygen charge-transfer band is also reported.