Publication Date

2014-11-26

Availability

Embargoed

Embargo Period

2016-11-25

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Chemistry (Arts and Sciences)

Date of Defense

2014-11-20

First Committee Member

V. Ramamurthy

Second Committee Member

Francisco Raymo

Third Committee Member

Burjor Captain

Fourth Committee Member

Linda S. Shimizu

Abstract

The research presented in this thesis reports various uses of supramolecules in steering photochemical and photophysical properties of small organic guest molecules. Crystals possess long range periodic arrangement of highly ordered building units and are considered as supramolecular systems. The first part of the thesis reports the use of crystals as a confined media (solid state) in directing photochemical reactions. In particular, olefins (trans 4-stilbazoles) have been directed to undergo selective [2+2] cycloaddtion in solid state. Selective photoproduct in crystals is controlled by various weak interactions in crystal lattice, which bring (pack) the reactive C=C bonds within 4.2 Å. Photoreaction is achieved by irradiating solid samples with UV light (>320 nm); products are analyzed by 1H NMR and crystal structure analysis. Although, trans 4- stilbazole molecules are photo inert, they have been directed to yield selective photoproduct (anti head-tail dimer) by forming 4-stilbazole. HCl. Crystal structure analysis of seven trans 4-stilbazole. HCl derivatives undoubtedly confirm that H2O molecules and Cl− plays an important role in packing the trans 4-stilbazole. HCl derivatives within reactive distance (Chapter 2). Our curiosity to understand the role of H2O molecules in the packing, drived us to study the photoreaction of anhydrous trans 4- stilbazole. HCl salts. The anhydrous stilbazole.HCl salts were either found to be photo inert or slow reacting compared to the H2O containing crystals and crystal structure analysis of the anhydrous crystals provided evidence of observed photoinertness or slow reaction. To investigate cis –trans isomerization in crystals we studied the photoreaction of cis 4-stilbazole. HCl in solid state (Chapter 3). cis –trans isomerization in crystals requiring ample molecular motion was achieved by irradiating solid samples of cis 4-stilbazole. HCl salts. 1H NMR studies of irradiated samples provide evidence of cis to trans isomerization and upon prolonged irradiation produce anti head-tail dimer. The second part of this thesis reports use of water-soluble supramolecular host molecules in solution (H2O). Our interest in exploring interaction between an excited organic molecule and gold atoms required us to synthesize water-soluble gold nanoparticles stabilized by water soluble hosts molecules (Chapter 4). Water soluble hosts known as octa acids (OA, ROA), each containing eight acid groups were effective in stabilizing water soluble gold-nanoparticles (~10 nm sized). Gold nanoparticles were characterized using UV-Vis, DLS, TEM, TGA, IR, and 1H NMR analysis. Guest inclusion within cavitand-functionalized nanoparticles resulted in quenching of excited singlet and triplet state due to the influence of gold via energy and electron transfer process. Although water soluble host molecules are already known to control and direct reactivity of small guest molecules, when encapsulated within the host cavity, its potential to act as electron donor/acceptor is not well explored (Chapter 5). We investigated the water-soluble host molecules OA and ROA and established their usefulness as an electron donor to positively charged electron acceptors (external guests) and also established their potential as a triplet sensitizer. Chapter 6 establishes that water-soluble gold-glutathione clusters (< 1nm size) can act as a good electron donor. Unlike gold nanoparticles, small sized gold clusters are emissive and low toxicity, ultra small size, and good biocompatibility, makes them ideal as imaging probes. Glutathione protected Au-clusters (~1 nm) are water soluble, has a strong emission around 600 nm and is established to be a good electron donor in the research discussed in Chapter 6.

Keywords

Cycloaddition, crystals as confined media, cis- trans isomerization, gold nanoparticles, gold nanoclusters

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