Abstract
Work presented in this thesis is the consolidation of our experiments aimed at controlling photochemistry of organic molecules using water soluble hosts, namely cucurbiturils and bile salts. The well defined cavities of cucurbituril macrocycles and the hydrophobic pockets of bile salt aggregates were utilized to control the outcome of photochemical reactions of a variety of molecules. Nanospaces provided by the host molecules were exploited to achieve selectivity with both unimolecular and bimolecular photochemical processes.Chapter 1 provides a brief overview of the origin, development and importance of supramolecular organic chemistry. The impact of this new area of research on other fields and its applicability is discussed with some examples. Research projects undertaken in our group that led us to investigate cucurbiturils and bile salt micelles to control photochemistry are presented here.Chapter 2 presents the results of photodimerization reactions of cationic organic olefins conducted within cucurbit[8]uril (CB[8]). The known ability of the cavity to complex to two cationic olefinic molecules was exploited to facilitate photodimerization reactions in aqueous phase. High dimer yields were achieved and selectivity in favor of a single photodimer over the others was observed. The chapter discusses the factors influencing the formation of a single dimer.Chapter 3 is the extension of the templating ability of CB[8] to orient and facilitate dimerization of neutral olefins. Complexation of cucurbiturils to neutral molecules is a less ventured aspect of the host family. Our experiments suggest that CB[8] is capable of including and orienting neutral trans cinnamic acids at dilute concentrations as observed by the high yields of photodimers. High selectivities were achieved in favor of a single dimer. Analysis of the obtained results in terms of cavity size of host, monomer orientations within the cavity and dimensions of the dimer with respect to that of the host sheds light on the origin of selectivity observed with cinnamic acid photodimerization reactions.Chapter 4 presents our attempt to control photochemistry of unimolecular reactions by employing physiologically important ampiphilic bile salts. The hydrophobic pockets were explored for their ability to contain photocleaved fragments (radicals) of short lived singlet and long lived triplet specks. Product distributions of the photochemical reactions conducted suggest that the bile salts are capable of restricting singlet radical pair but fail to control the long lived triplet radical pair processes. We propose that the size of bile salt aggregates and the rate of equilibrium of the monomer bile salt with the aggregates is probably the deciding factor for the observed selectivity.