Examination of the nitromethane selective quenching rule in micellar anionic sodium dodecylbenzenesulfonate and micellar cationic dodecylethyldimethylammonium bromide solvent media

Abstract

Abstract. Applicability of the nitromethane selective quenching rule for discriminating between alternant versus nonalternant polycyclic aromatic hydrocarbons (PHAs) is examined for 38 representative PAH solutes dissolved in micellar sodium dodecylbenzenesulfonate (SDBS) and in micellar dodecylethyldimethylammonium bromide (DEDAB) solvent media. Experimental results show that nitromethane quenched fluorescence of only the 20 alternant PAHs in the cationic DEDAB surfactant solvent media as expected. Emission intensities of nonalternant PAHs, except for the few borderline cases noted in previous work, were unaffected by nitromethane addition. Unexpected quenching behavior was observed, however, in the case of nonalternant PAHs dissolved in micellar sodium dodecylbenzenesulfonate solvent media. Nitromethane quenched fluorescence emission of all 18 nonalternant PAHs studied in the SDBS solvent media, which is contrary to the selective quenching rule.Key words: fluorescence quenching, micellar solvent media, nitromethane selective quenching rule, anionic surfactants, cationic surfactants.This study continues a systematic examination of the effect that solvent media and substituent functional group has on the ability of nitromethane to selectively quench fluorescence emission of altemant polycyclic aromatic hydrocarbons (PAHs). Emission intensities * To whom correspondence should be addressed More recent measurements [9,10] revealed that nitromethane quenched fluorescence emission of all eighteen acenaphthylene-and acephenanthrylenederivatives studied thus far which is completely contrary to what would be expected based upon the fact that the solutes are listed as "textbook" examples of nonalternant PAH molecules. Solutes are classified as alternant PAHs if every alternant carbon atom in the aromatic ring system can be "starred". Nonalternant PAHs, on the other hand, would have at least one pair of adjacent starred atoms [11,12]. The unusual fluorescence quenching behavior of the acenaphthylene-and acephenanthrylene-derivatives results from the molecules' fixed double bond in the five-membered ring. The double bond is alkenic in nature, rather than aromatic as one might believe and should not be included as part of the aromatic ring system when determining whether the compound is an alternant versus nonalternant PAH. This observation is confirmed by independent NMR coupling measurements [13][14][15][16]. Moreover, for cyclopent[fg]acenaphthylene, where movement of the double bonds in the two cyclopenta-rings leads presumably to a valid fourth resonance structure, Freiermuth et al. [17]

Smart Shell‐by‐Shell Nanoparticles with Tunable Perylene Fluorescence in the Organic Interlayer

“…Reason for that phenomenon is an electronic communication between the pyridinium and the perylene unit. Pyridinium quenches the fluorescence of the perylene through a photo‐induced electron‐transfer (PET) from the excited state of the perylene, that was formed during excitation with light of 408 nm, towards the nitrogen atom of the pyridinium, that has a lowered LUMO energy level compared to that of the perylene [6a,b,d,e, 19] …”

Fluorescence Quenching of Polycyclic Aromatic Hydrocarbons by Nitromethane within Ionic Liquid Added Aqueous Anionic Micellar Solution

“…k q , on the other hand, follows a trend similar to K D and, in the absence of [bmim][BF 4 ], reaches close to diffusion-controlled value. This is expected for favorable quenching of alternant PAHs by nitromethane within aqueous anionic micellar SDS media. ,,,, …”

“…In order to identify, separate, and detect alternant and nonalternant PAHs, fluorescence spectroscopy offers high sensitivity and selectivity because the quantum yield of most PAHs is quite significant. Zander, − Acree, − and McGuffin − groups have shown that nitromethane selectively quenches the fluorescence of alternant PAHs as opposed to the fluorescence of nonalternant PAHs. In a series of publications, Acree and co-workers using several alternant and nonalternant PAHs have amply established the nitromethane selective quenching rule. − , …”

“…Zander, − Acree, − and McGuffin − groups have shown that nitromethane selectively quenches the fluorescence of alternant PAHs as opposed to the fluorescence of nonalternant PAHs. In a series of publications, Acree and co-workers using several alternant and nonalternant PAHs have amply established the nitromethane selective quenching rule. − , …”

Spectrochemical Evaluation of Diisopropylamine as a Selective Fluorescence Quenching Agent of Polycyclic Aromatic Hydrocarbons in Acetonitrile

“…Therefore, primary inner filter artifacts can become problematic in the detection of these compounds. Also, nitromethane selective quenching is lost when the PAHs are in the presence of anionic surfactants above their critical micelle concentration (31)(32)(33). It is interesting to note that the selective quenching ability of nitromethane is retained in anionic, carboxylate terminated poly(amido) amine dendrimers, which are referred to as unimolecular micelles (30).…”