The binding dynamics with bile salt aggregates for a series of naphthalene derivatives of different polarities was studied using fluorescence and laser flash photolysis. Fluorescence was employed to determine the nature of the binding site for each guest and the accessibility of the bound guest to quenchers. Laser flash photolysis was employed to study the mobility of the triplet states of the naphthalenes between the sodium cholate aggregates and the aqueous phase. Primary aggregates, which provide an environment protected from quenchers in the aqueous phase, bind 1- and 2-ethylnaphthalene as guests. The complexation dynamics with this type of aggregate is slow. 1- and 2-Naphthyl-1-ethanol, and 1- and 2-acetonaphthone bind to the secondary aggregates, which provide moderate protection from quenching and faster binding dynamics. The addition of salts lowered the cholate concentration at which primary aggregates were formed, but did not influence the formation of secondary aggregates.

The reactivity of excited benzophenone (Bp) and 4,4‘-dimethylbenzophenone (DMBp) in the presence of sodium cholate (NACh) aggregates was studied by following the kinetics of the excited triplet states and the ketyl radicals of both ketones. At low NACh concentrations only primary aggregates are present in solution. The ketyl radicals were formed from the reaction of the triplet ketones bound to the primary sites. The decay of the ketyl radicals occurred primarily by the reaction of these radicals in water. Some long-lived triplets included in the primary aggregate were also observed. A different reactivity was observed at higher NACh concentrations where secondary aggregates are present. The binding process associated with the secondary binding sites is much faster than for the primary site. The hydrogen abstraction reaction in the secondary binding site is too slow to compete with the exit process, but self-quenching competes efficiently, leading to a shortening of the triplet lifetimes for both ketones. From the dynamic results it was concluded that only a small number of NACh molecules (8−13) are needed to define the primary and secondary binding sites.

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The photochemistry and photophysics of several psoralens and coumarins have been examined in human serum albumin (HSA) complexes and dimyristoylphosphatidylcholine (DMPC) vesicles. Fluorescence spectroscopy indicates that there are multiple binding sites with polarities that are intermediate between those of acetonitrile and water for the substrates complexed to HSA. In the case of the 6,7-dimethoxycoumarin-HSA complex, laser flash photolysis experiments provide evidence for the formation of radical cation in addition to triplet. Radical cations are not detected for other coumarin-HSA complexes, either due to a lower yield of formation or to rapid reaction of an initial radical cation with adjacent amino acids. Fluorescence spectra for coumarins indicate that they are primarily solubilized in the polar headgroup region in DMPC vesicles. Consistent with this, radical cations generated by photoionization are detected in transient experiments. For dimethoxycoumarins the radical cation is long-lived, indicating rapid exit from the vesicle and decay in the aqueous phase. However, 4,5',8-trimethylpsoralen and 7-ethoxy-4-hexadecylcoumarin radical cations are much shorter-lived, presumably due to rapid decay by electron recombination in the vesicle. The results for both HSA complexes and vesicles indicate that radical ions may play a role in psoralen and coumarin photochemistry in a cellular environment.