Development of New Photoacid Generators and Photoremovable Protecting Groups.
The goal of this research is to develop both a reversible and an irreversible photoacid generator (PAG). The reversible PAG will increase acidity when photolyzed, but in the dark it will revert back to the starting material. The irreversible PAG on the other hand will release the acid irreversibly when photolyzed. The irreversible PAGs will be further developed into a photoremovable protecting group (PRPG).
PAGs and PRPGs will use light as a catalyst for affecting a pH change, or introduction of small molecules that can be used in many applications (e.g. polymer synthesis and photolithography). The proposed reversible PAG, 2’-(2-acetyl-phenyl)-ethanone derivative 1 (fig. 1), irreversible PAG 2a and 2b will be photolyzed by 5 ns laser pulses from an Nd:YAG laser (266 nm), and the quantity and kinetics of acid released will be measured by determining the absorbance of Rhodamine B base at 550 nm or methyl red at 500 nm.
For irreversible PAGs, a 350 W Hg lamp will be used to release the acid, while the detection strategies would be the same. Isolation of the side product (expected to be 2-acylstyrene derivatives) will help establish the mechanism of the acid release. The irreversible PAG also has the potential to be a good PRPG (2b and 2c). Various carboxylic acids, alcohols, and amines will be protected by this group and their photorelease will be attempted. The mechanism and rate of release will be followed by transient spectroscopy.
REPRESENTATIVE PUBLICATIONS
Atemnkeng, W. N.; Louisiana, L. D.; Yong, P. K.; Vottero, B.; Banerjee, A. “1-[2-(2-Hydroxyalkyl)phenyl]ethanone: A New Photoremovable Protecting Group for Carboxylic Acids.” Organic Letters , 2003 , 5(23) , 4469-4471.
