SELECTIVE FLUORESCENCE QUENCHING TO DISCRIMINATE BETWEEN ALTERNANT AND NONALTERNANT POLYCYCLIC AROMATIC-HYDROCARBONS - ACEPHENANTHRYLENE DERIVATIVES AS EXCEPTIONS TO THE NITROMETHANE QUENCHING RULE

Nitromethane selectively quenches the fluorescence emission of alterna nt polycyclic aromatic hydrocarbons (PAHs) via an electron transfer me chanism. Emission intensities of nonalternant PAHs, for the most part, are unaffected. Results of previous measurements show that nitrometha ne does quench the fluorescence emission of the nine acenaphthylene so lutes studied, which is completely contrary to what would be expected based on the fact that ail nine solutes are nonalternant PAHs. To inve stigate this phenomenon further, the fluorescence behaviour of 1-, 3-, 4-, 5-, 6-, 7-, 8-, 9- and 10-methylacephenanthrylene dissolved in ne at acetonitrile, acetonitrile-ethyl acetate and acetonitrile-toluene s olvents was measured at different nitromethane concentrations. Experim ental results support the notion that the double bond in the five-memb ered ring is fixed; therefore, the solutes act as alternant rather tha n non-alternant PAHs.