Supramolecular control during triplet sensitized geometric isomerization of stilbenes encapsulated in a water soluble organic capsule

Triplet sensitized photoisomerization of several stilbenes included within a water-soluble organic capsule has been investigated. In this study octa acid that self assembles in the presence of hydrophobic guest molecules to form a host-guest complex is utilized to solubilize hydrophobic stilbenes and triplet sensitizers in water, and to provide confinement during the geometric isomerization of included olefins. By monitoring the steady state and time resolved room temperature phosphorescence from 4,4'-dimethylbenzil in the presence of acceptor stilbenes and their nitrogen analogues (stilbazole and bispyridyl ethylene) we have been able to establish that triplet-triplet energy transfer occurs between encapsulated donors and encapsulated (or free) acceptors. The mechanism of the energy transfer process is yet to be fully understood although a similar phenomenon has been reported earlier in the literature with Cram's hemicarcerand as the host. The photostationary state composition of cis and trans isomers within the OA capsule is dependent on the relative binding strength of the two isomers with the OA capsule. Further investigation is needed to fully exploit the interesting observations made here to steer the photoisomerization towards a single isomer.