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 alternant polycyclic aromatic hydrocarbons (PAHs) via an electron transfer mechanism. Emission intensities of nonalternant PAHs, for the most part, are unaffected. Results of previous measurements show that nitromethane does quench the fluorescence emission of the nine acenaphthylene solutes studied, which is completely contrary to what would be expected based on the fact that ail nine solutes are nonalternant PAHs. To investigate this phenomenon further, the fluorescence behaviour of 1-, 3-, 4-, 5-, 6-, 7-, 8-, 9- and 10-methylacephenanthrylene dissolved in neat acetonitrile, acetonitrile-ethyl acetate and acetonitrile-toluene solvents was measured at different nitromethane concentrations. Experimental results support the notion that the double bond in the five-membered ring is fixed; therefore, the solutes act as alternant rather than non-alternant PAHs.