Date of Award
Doctor of Philosophy (PhD)
Fluorinated functional groups have attracted great interest in various aspects of chemistry applications including pharmaceuticals, organic electronics, and polymers. The aim of this study is to explore the impact of fluorinated functional groups on 1) optimization of crystal structures and electronic properties of organic semiconductor molecules, 2) electrochemical polymerization of fluorinated aromatics, 3) photochemical reactivity of carbonyl compounds, and 4) generating new nucleophilic fluorination reagents. Our initial work demonstrates that long fluoroalkyl side chains on planar aromatic systems give rise to fluorine-fluorine (F---F) attractive interactions, assisting formation of lamellar packing motif in the solid state. Surprisingly, introducing shorter perfluoroalkyl side chains, including trifluoromethyl and pentafluoroethyl, onto planar phenazine molecules could also result in modulating crystal packing motifs, yet fine tuning electronic parameters associated with charge transfer. Significant differences in crystal packing of small to large planar fused aromatic molecules were observed by combined effect of perfluoroalkyl side chains with mild electron donating functional groups. The role of fluorine on crystal structure of planar aromatics was also assessed by determining crystal structures of unsubstituted and corresponding n-alkyl substituted molecules. Perfluoroalkyl side chains also enabled electrochemical polymerization of these phenazine derivatives likely caused by its initial reductive defluorination after electrochemical reduction. Fluorinated functional groups also imparted enhanced photochemical reactivity of phenanthrenequinone (PQ), where fluorinated PQ derivatives formed diphenic anhydrides in presence of light and air. Electron deficient fluoroaromatic compounds was explored for generating of anhydrous fluoride in-situ that could effectively conduct room temperature nucleophilic fluorination. This is achieved by nucleophilic attack of a dimethylaminopyridine (DMAP) nucleophile on tetrafluorophthalonitrile (TFPN), resulting in generation of anhydrous fluoride in association with pyridinium organic counter ion. Efficient halogen exchange for both aliphatic and aromatic halides were observed with this new fluorinating reagent. Preliminary experiments showed that this new anhydrous fluoride salt is also capable of driving deoxyfluorination of alcohols when extra TFPN is presented. Further study is under way in our laboratory to explore the reaction mechanism and substrate scope.
Electrochemical polymerization, Fluorinated functional materials, Nucleophilic fluorination reagent, Organic semiconductors, Perfluoroalkylation, Photochemistry
Number of Pages
University of South Dakota
Gairhe, Shankar, "CHEMISTRY OF FLUORINATED FUNCTIONAL GROUPS: IMPACT ON MOLECULAR PACKING, OPTOELECTRONIC PROPERTIES, ELECTROCHEMICAL POLYMERIZATION, PHOTOCHEMISTRY, AND REAGENT DEVELOPMENT" (2023). Dissertations and Theses. 179.
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