PHOTOGENERATION OF ORGANIC-BASES FROM ORTHO-NITROBENZYL-DERIVED CARBAMATES

The design of novel photoprecursors of organic bases and the steric and electronic factors that control their quantum-efficient transformation into free amines or diamines have been investigated. The basic design involves the protection of amines with photolabile [(o-nitrobenzyl)oxy]carbonyl groups or alpha-substituted analogues. The resulting protected amines owe their light sensitivity to the classical o-nitrobenzyl photorearrangement and cleanly liberate free amine in both the solid state and in solution upon irradiation with UV light below 400 nm. Several designs were explored in which the structure of the photoactive center was varied systematically to investigate the influence of various steric and electronic effects. In all cases, the practical potential of these photoactive carbamates as organic sources of photogenerated base was evaluated by product analysis of solution photolysates, by determination of their solid-state quantum efficiencies, and by measurement of their thermal properties. For example, the quantum efficiency of various carbamates for cyclohexylamine photogeneration at 254 nm ranged from 0.11 to 0.62 depending on both alpha-substituent and o-nitro substitution patterns, confirming the importance of both steric and electronic considerations. Similar results were obtained with other base photoprecursors and all showed good thermal stabilities.