Date of Award

2013

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

William B. Euler

Abstract

Explosive analytes and their decomposition products are of great interest to the scientific community, in large part due to events of international terrorism and warfare, but also as environmental pollutants. Chapter 1 of this dissertation shows for the first time that the hydroxide adducts of trinitrobenzene (TNB) and trinitrotoluene (TNT), TNB-OH– and TNT-OH–, are emissive while TNT– is not. This has great impact on pre-existing sensors, which may be affected negatively by an increase in emission competing with the observation of a quench. Additionally, we described a competing reaction with the solvent, N,N-dimethylformamide (DMF), which is also capable of nucleophilic attack upon TNT and observable due to its overwhelming quantity.

Chapter 2 of this dissertation shows the similarities of TNT products formed by OH– exposure and amine exposure, covering a wide variety of amines. 1H NMR and rapid absorbance measurements showed formation of TNT– or TNT adducts, the relative rates of which are observed to be strongly dependent on solvation. Intrinsic rate constants in methanol implied that all amine reactions were forming the same adduct (TNT-OCH3–). The credibility of amine adduct formation was further explored in Chapter 3 through computational approaches. High level ab initio calculations were performed to obtain models of reactants and products of the investigated reactions, and their relative energies and thermodynamic quantities were computed. The data showed a striking disparity in the calculated thermodynamics, with OH– and OCH3–adduct formation being much more favorable than amine adduct formation. Charge

transfer (CT) complexes between TNT and the explored amines were converged and also found to be of higher energy than alkoxide adducts.

In Chapter 4, a sensing array based on highly fluorescent reporter molecules in DMF solution is described. Eight xanthene-based fluorophores were chosen based on their high quantum yields, and their interactions with twelve relevant explosive analytes were interpreted through absorbance and emission data. The resulting array showed promise in observing an identifying "fingerprint" response to each class of analyte, with the largest responses coming from the formation of TNB and TNT products. In addition, these products were observed to be involved in an electron transfer (ET) mechanism where they donated energy to cationic fluorophores, enhancing the fluorophores' emission.

The findings of this dissertation indicate the need for caution in TNT sensor development, as trace water provides OH– and common solvents are capable of competing for TNT reactivity. Trace water should be monitored and minimized for appropriate sensor testing and subsequent use, and solution based sensors require an understanding of solvent competition. Amines are not capable of direct deprotonation of TNT, and do not compete significantly with OH– or alkoxides in forming a sigma adduct with TNT. Rather, the formation of colorful complexes that has been attributed to a TNT-NR3 adduct in the literature is due to the deprotonation of ambient water or solvent molecules, which in turn react with TNT. Finally, xanthene-based fluorophores may selectively interact with explosive analytes, with trinitroaromatic products capable of electron transfer to fluorescent reporters leading to emission enhancement.

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