Understanding the Interior Characteristics of a Deep Cavity Cavitand and Its Role in Modulating Photophysical Processes of Organic Molecules

The central tenet of this thesis is to explore the use of a deep cavity cavitand known by the trivial name octa acid as a reaction cavity for manipulating photochemical and photophysical properties of organic molecules. The micropolarity of the interior of the cavitand was monitored by recording the fluorescence of different polarity probes. They all indicated that the interior of octa acid capsuleplex (2:1, host/guest complex) is nonpolar and does not contain water molecules despite the complex being present in water. Photophysical and NMR experiments suggested that the structure of the host/guest complex depends on the size and hydrophobicity of the guest molecule. We also probed the dynamics of guest molecules included within octa acid with the help of 1H NMR and EPR techniques. We have studied the photoinduced electron transfer from the donor incarcerated within octa acid nanocapsule to the acceptor free in solution. Comparison to the electron transfer in free solution showed significantly accelerated dynamics and essentially no solvent relaxation when the donor was encapsulated into the host molecule. In that context we were able to bind a dye molecule encapsulated within OA capsule to the semiconductor (TiO2) and hence monitor electron transfer from the dye to the semiconductor. The molecular communication between two molecules, one confined and excited (triplet or singlet) and one free and paramagnetic was studied through quenching of fluorescence and/or phosphorescence by nitroxides as paramagnetic radical species. Results presented in this thesis highlight the role of the lifetime of the encounter complex in electron-electron spin communication when the direct orbital overlap between the two molecules was prevented by the intermediary wall. In a separate work, we have shown that the high-energy axial conformer of propyloxy-substituted piperidine gets stabilized within octa acid capsule, which highlights the value of confined spaces in physical organic chemistry. This work also spans disciplines to understand the complexation patterns between nitroxides and cucurbiturils. One of the key findings of this work was that a selective triangular geometry of the supramolecular aggregate ([nitroxide@cucurbit[8]urils]3) leaded to spin exchange between the three radical centers. The use of supramolecular architectures to control the spatially dependent spin exchange between two/three covalently linked radical centers (biradicals/triradical respectively) has been explored