Caged molecules, molecules deactivated by photoremovable “protecting groups”, have served many useful purposes in chemistry, in biology and more recently in medicine. The major focus for applications has been to develop a chromophore that is readily appended to a reactive agent. The assembly is then directed to a desired destination where the chromophore is readily removed by light. Lost in the search for “ideal” caging chromophores has been attention to the complex series of events which the chromophore must pass through during and after the release event. We have examined important influences on not only the activation processes (solvent, pH, O2, one or two photon excitation, and supermolecular enclosure), but also effects of environment on the chemical fate of the chromophore. While this has been of minor interest or neglected in most studies, especially where the release of the substrate is robust, it has become apparent that the presence of complex biological hosts and chemically sensitive reagents may react with the chromophore shrapnel resulting in unwanted reactions and byproducts. In our studies on the mechanisms of the photorelease of substrates from several cages, i.e., p-hydroxyphenacyl (pHP) and p-methoxyphenacyl (pMeOP), 7-methoxycoumar-4-methyl (MCH), and 7-diethylaminocoumaryl-4-methyl (DEACM), we have discovered that the spent chromophore is not always a benign spectator. Careful investigations of byproducts of the chromophore reveal a diverse series of pathways emerge depending on the environment, the presence or absence of O2, and even the released substrate. Key examples of our studies will be detailed.

Interrogating the photochemistry of caged functional groups: Hidden mechanistic variations

255th National Meeting (2018)

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