Quenching of alkanone fluorescence by alkyl halides in cyclohexane solution

Abstract

Alkyl halides were found to quench the fluorescence of both acetone and butan-2-one in cyclohexane solution. The fluorescence quenching rate constant (k_Q) did not correlate with either the spin–orbital coupling constant of the halogen atom or the ionization potential of the alkyl halide quencher. Substituted benzyl halides were also effective quenchers for butan-2-one fluorescence and the results obtained indicated that iodo-compounds acted as electron donors and chloro-compounds as electron acceptors in the fluorescence quenching mechanism. The results implied an excited state complex formed between alkanone singlets and the alkyl halide quencher which was stabilized by charge transfer interactions. The carbon–halogen bond provided a convenient vibrational energy sink which enabled the complex to decay via radiationless decay processes.