Effect that Various Electron Donating and Electron Withdrawing Functional Groups have Regarding Nitromethane's Ability to Selectively Quench Fluorescence Emission of Alternant Polycyclic Aromatic Hydrocarbons

Abstract

Nitromethane selectively quenches fluorescence emission of alternant polycyclic aromatic hydrocarbons (PAHs) via an electron transfer mechanism. Emission intensities of nonalternant PAHs, for the most part, are unaffected. To better understand the quenching mechanism, the fluorescence behavior of 1-methylpyrene, 2-methylpyrene, 4-methylpyrene, 1,5-dimethylpyrene, 1-butylpyrene, 1-decylpyrene, 1-pyrenebutanoic acid, 1-chloropyrene, 1-aminopyrene, 3,4,5-trihydrobenzo[cd]pyrene, 1-pyrenecarboxaldehyde, 1,3-pyrenedicar-boxaldehyde, 3,6-dicyanobenzo[e]pyrene, 5,6,7,8,9,10-hexahydrobenzo[ghi]perylene, 4H-benzo[e]cyclopenta [1]pyrene, 3,4-dihydrobenzo[ghi]perylene, 4,5,6,7-tetrahydro-4,7-methanodibenzo[fg,op] naphthacene, 8b,9,10,11,12,12a-hexahydro-9,12-methanobenzo[e]pyrene, 5-methyldibenzo[b,def]chrysene, 5-methyl-chrysene, 4-methylchrysene, 2-methylanthracene, 9,9′-bianthracene-10-carboxaldehyde, 3-perylenecar-boxaldehyde, and 1-acetylcoronene dissolved in neat acetonitrile, toluene-acetonitrile and ethyl acetateacetonitrile solvents was measured at different nitromethane concentrations. Experimental results show that strongly deactivating, electron withdrawing substituents can favorably alter the molecular orbital energies and/or reduction potentials so as to prevent electron transfer from the substituted alternant PAH molecule to nitromethane, which acts as the electron acceptor in the presumed quenching mechanism. Also included is a discussion of the fluorescence behavior of select pyrene derivatives in organic nonelectrolyte solvents of varying polarity.