Year of Publication

2012

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Arts and Sciences

Department

Chemistry

First Advisor

Dr. Arthur Cammers

Abstract

This dissertation focuses on the design and study of charged aromatic molecules where weak π-π interactions synergize with electrostatic interactions to enhance the overall interaction between aromatic moieties. Each chapter investigates some aspect of this hypothetical synergy between electrostatics and π-face aromatic cohesion.

The first chapter unveiled the importance of electrostatics in the intramolecular stacking of flexible aromatic molecular templates 1-2Br and 2a. While our previous studies found dicationic molecular template 1-2Br to have intramolecular π-stacking between electron poor pyridinium and electron rich xylylene moieties, no such stacking interaction was observed in the neutral analog 2a.

Chapter two systematically explored the stacking pattern of electron poor aromatics in the form of oxygen- and / or nitrogen- substituted triangulenium cations, [1(NR)3]+ and [1(O)3(OH)3]+. As indicated in the chemical literature, triazatriangulenium cations [1(NR)3]+ with N- ethyl (and longer alkyl chains) chains were found to pack as face-to-face dimers. This study found the formation of columnar, face-to-face, n-meric association between aromatic cations in the structures with decreased steric interactions of the side chains in the stacking planes ([1(NMe)3]+ and [1(O)3(OH)3]+). Similar iso-structural triangulene based aromatic anions, (2)- and (3)2- didn’t indicate any facial interactions in the solid states.

The possible synergy between unit charge electrostatics and π-face aromatic interactions was explored in aromatic ion pairs 1•2 of triangulene based aromatic cations and aromatic anions. This charge-assisted π-π stacking seems to be the novel way of getting strong π-system interactions where the strongest non-covalent force and the weakest non-covalent force: ionic bonding and π-stacking respectively synergize together. The π-π interaction between ionic aromatics in the solid state was investigated by means of single crystal x-ray diffraction and powder x-ray diffraction (PXRD). The interaction in the solution state was examined by UV-Vis spectroscopy, electrospray ionization mass spectroscopy (ESI-MS) and electrochemical studies. Studies found that optimal synergy was possible only in the ion pairs with no steric interactions of alkyl (or aryl) side chains in the stacking planes (1(O)32 & 1(NMe)32) and the interaction was found to be comparable with the strongest radical-assisted π-stacking described in the chemical literature.

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