Quenching of the singlet and triplet state of benzene in condensed phase

Quenching of the fluorescence of benzene by halocarbons in methanol, ethanol, acetonitrile, and cyclohexane has been investigated. It proceeds via a reversible exciplex intermediate formed between excited singlet benzene and ground state halocarbon. Quenching is controlled by the polarity of the medium. Excited singlet benzene interacts with acetonitrile solvent and a longer wavelength emission due to this complex is observed.The effect of CCl4, CH3CN, CHCl3, and CH3CCl3 on the triplet and singlet excited states of benzene in a methylcyclohexane–isopentane mixture at 77 K has been examined. Carbon tetrachloride and acetonitrile are far more effective quenchers than either CHCl3 or CH3CCl3. In the case of the latter pair enhanced intersystem crossover competes with complex formation.