Ultrafast time-resolved spectroscopy and time-resolved resonance Raman spectroscopy experimental results in the picoseocond timescales are reported for selected p-hydroxyphenacyl (pHP) ester phototrigger compounds. The results better elucidate the photodeprotection and rearrangement reactions of these important phototriggers and an overall mechanism is proposed for these reactions based on the time-resolved spectroscopy data presented here. This work indicates that site-specific, concerted solvation of the hydroxy proton and phosphate-leaving anion group through their respective intermolecular H-bonding with solvent water molecules promotes the photodeprotection reaction.