Choose your leaving group: selective photodeprotection in a mixture of pHP-caged compounds by VIPER excitation

Photocages are light-triggerable molecular moieties that can locally release a pre-determined leaving group (LG). Finding a suitable photocage for a particular application may be challenging, as the choice may be limited by for instance the optical or physicochemical properties of the system. Using more than one photocage to release different LGs in a reaction mixture may even be more difficult. In this work an experimental strategy is presented that allows us to hand-pick the release of different LGs, and to do so in any order. This is achieved by using isotopologue photocage-LG mixtures in combination with ultrafast VIbrationally Promoted Electronic Resonance (VIPER) excitation. The latter provides the required molecular selectivity simply by tuning the wavenumber of the used IR pulses to the resonance of a specific photocage isotopologue, as is demonstrated here for the para-hydroxyphenacyl (pHP) photocage. For spectroscopic convenience, we use isotopologues of the infrared (IR) spectroscopic marker -SCN as different LGs. Especially for applications where fast LG release is required, pHP is found to be an excellent candidate, as free LG formation is observed to occur with a 10 ps lifetime. The devised strategy may open up new complex uncaging applications, where multiple LGs can be formed locally on a short time scale and in any sequence.