Investigations on 2,7-diamino-9-fluorenol photochemistry

Photoremovable protecting groups have been long known as useful synthetic tools. They are commonly linked to a substrate of interest to make them unable to react, forming in this manner a “caged compound”. Upon irradiation the protecting group undergoes a photochemical reaction that results in release of the substrate and restores its activity. The main goal of this work was that of identifying a system that would efficiently release alcohol, as this could be readily applied in biology. The idea was based on the photochemistry of 9fluorenol which is well established and known. 2,7-diamino-9-fluorenol was efficiently synthesized and LFP investigations were carried out to clarify the reaction mechanism in different solvents. Transients in the infrared area were observed in the solvents TFE and HFIP but their character remains unclear. We suspect their cationic character, and their formation either via singlet or a very fast triplet state. Our mechanistic studies provided rate constants of formation and decay of the transients in three different solvents (TFE, methanol and water). Two derivatives of 2,7-diamino-9-fluorenol (X = C6H5 and COCH3) were synthesized using a four-step synthetic route. The photorelease of these derivatives was elucidated by employing irradiation experiments and product analysis. The results indicate that 2,7diamino-9-fluorenyl acetate liberates acetic acid efficiently whereas the efficiency rate of release of 2,7-diamino-9-fluorenyl phenyl ether is low.