Our research group view the photon as a reagent for initiating photoreactions and as a product of the deactivation of electronically excited molecules. Photons as reagents possess some outstanding properties, e.g., they may be used to selectively excite specific groups of atoms in a single molecule or specific molecules in a mixture, because the absorption of light depends on specific electron energy gaps which are unique to groups of atoms in a molecule or to specific molecules. This selectivity of photon absorption may be controlled and varied at will by use of lasers or a monochrometer. The concentration of photons may be varied at will by controlling the light intensity. Photons can even be made optically active by the use of polarizers! Finally, by use of pulsed lasers, high concentrations of photons can be injected into a system to trigger reactions in times as short as a trillionth of a second (a picosecond).

We employ photons to study the structure and dynamics of a range of reactive intermediates such as carbenes, radical pairs, singlet oxygen, and biradicals. These species are produced by photochemical excitation and their chemistry is investigated by a range of time resolved techniques (such as laser flash photolysis and TR-ESR). These techniques are employed to determine the chemistry of these reactive intermediates when they are confined to the restricted reaction spaces of micelles (aggregates formed from the association of detergent molecules in aqueous solution), zeolites (crystalline porous solids), starburst dendrimers (giant molecules having micellarlike properties) and biological molecules such as DNA.

Our group is developing a novel field termed "supramolecular" photochemistry, or photochemistry beyond the conventional intellectual and scientific constraints implied by the term "molecule". In supramolecular processes non-covalent bonds between molecules play a role analogous to that of covalent bonds between atoms. Supramolecular photochemistry of reactive intermediate has proven to be a very rich area for the discovery of novel effects for which very small amounts of materials or very small amounts of energy can produce very significant and novel chemical effects. For example, when ketones are photolyzed in the restricted spaces of micelles or zeolites, significant magnetic field effects are observed. Even a magnetic stirrer bar can dramatically influence chemistry under these conditions, and 13-C, a magnetic nucleus, can direct reactions which 12-C, a non-magnetic nucleus, cannot! As another example, photoinduced electron transfer between metal complexes associated with DNA has been found to occur over very large distances (> 40 Angstroms). These results suggest that the DNA structure itself can serve as a "wire" to conduct electrons between an electron donor and an electron acceptor. Such processes have important potential applications and implications for processes in biology.

As a final example, radical pairs produced in zeolite cavities containing a chiral guest causes the pair to recombine in an enantiomeric selective manner, opening a novel means of producing optically active molecules.