The externally controlled cleavage of covalently linked prodrugs, proteins, or solid-phase formulation vehicles offers potential advantages for controlled drug or gene delivery. A series of o-nitrobenzyl ester compounds (1–8) were synthesized to allow a systematic study of photolability. The o-nitrobenzyl ester was strictly required for photolability, while imido esters were not photolabile. The degradation kinetics of 1-o-phenylethyl ester was an order of magnitude faster than that of o-nitrobenzyl ester. Tosylate, phosphate, and benzoate derivatives of 1-o-nitrophenylethyl displayed similar photolability (>80% decomposition within 10min at 3.5mW/cm 2 at 365nm). O-o-Nitrobenzyl O′,O″-diethyl phosphate displayed the fastest decomposition at photoirradiation condition (3.5mW/cm 2 , 365nm) suitable for biological systems. We report the synthesis and photo-decomposition of 1-o-nitrophenylethyl derivatives amenable for the creation of photolabile prodrugs or formulation particles for drug depots, DNA condensation, or tissue engineering applications.