Nitromethane is examined as a selective quenching agent for discriminating between "alternant" versus "nonalternant" polycyclic aromatic hydrocarbons in unknown mixtures. Of the 36 benzenoid solutes studied, only dibenzo[hi,wx]heptaphene failed to obey the selective quenching rule. Also reported are new experimental fluorescence probe studies for dibenzo [de,st]
Fluorescence emission spectra are reported for naphth[2',l',8',7':4,10,51anthra [1,9,8cdeflcinnoline, benzo[lmnl[3,81phenanthroline naphth[2',l',8',7':4,10,51anthra[1,9,8cdeflcinnoline exhibits some signs of probe character as evidenced by changing emission intensity ratios; however, numerical values did not vary systematically with solvent polarity. The effect of nitromethane and 1,2,4-trimethoxybenzene as selective quenching agents on both the unprotonated and protonated PANHs was also examined. Nitromethane was found to quench fluorescence emission of roughly two-thirds of the alternant unprotonated PANHs studied to date. Emission intensities of the protonated PANHs remained essentially constant and were not affected by nitromethane. 1,2,4-Trimethoxybenzene, on the other hand, quenched the fluorescence emission of several unprotonated and all protonated PANHs examined.
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