Publication Date

2015-04-30

Availability

Embargoed

Embargo Period

2017-04-28

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Chemistry (Arts and Sciences)

Date of Defense

2015-04-20

First Committee Member

V. Ramamurthy

Second Committee Member

Burjor Captain

Third Committee Member

James N. Wilson

Fourth Committee Member

Abraham Joy

Abstract

The research work presented in this thesis is a consolidated report of experiments carried out to emphasize the superiority of supramolecular host systems in controlling the photochemical and photophysical properties of organic guest molecules. A well explored supramolecular host in our group called by its trivial name “octa acid” (OA) has been utilized in major part of this work. OA is a water soluble deep cavity cavitand having benzene like inner cavity. The ability of two OA molecules to self assemble in the presence of hydrophobic guest to form a capsule has been exploited to carry out photoreactions of various neutral organic guest molecules inside its confined space. We have synthesized two new water soluble deep cavity cavitands having same skeleton of OA. These new cavitands were found to have very similar features as that of OA in terms of their influence in controlling the photochemical and photophysical properties of various guest molecules. Our attempt to carry out triplet sensitized photoisomerization of para-substituted stilbenes within the OA capsule using water soluble triplet sensitizers of different kind has turned out to be useful in understanding the control exerted by OA in this process. The information obtained from this study also gives some insight into the triplet energy transfer mechanism that occurs between an incarcerated acceptor and free donor. Irradiation of OA complexes of benzonorbornadiene and dibenzobarrelene yielded only triplet products which confirm the triplet sensitizing ability of OA. Results presented in this thesis highlight the role of light in the OA capsular disassembly process by using appropriate phototriggers. In this study, a photochemical β-cleavage process centered on the p-substituted phenacyl group was exploited to release the acid of interest from OA capsule. The efficiency and nature of the photoproducts obtained can be altered by just changing the functional groups on the phenacyl part of the guest. Photolysis of nitrene precursors inside OA capsule produced highly reactive nitrenes and due to their restricted mobility, these nitrenes took selective path to obtain selective products. Our attempts to form host-guest complexes between hosts iTATA and TATP in their neutral form with various guests on an inert surface like SiO2 were found successful in the presence of water. NMR, TEM and UV-Vis experiments on OA functionalized gold nanoparticles gave some useful information about their nature and stability.

Keywords

Supramolecules; Photochemistry; gold nanoparticles; host-guest; capsules; excited state

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