Title

Investigating the Photochemistry of Azobenzene and Nitrobenzyl Compounds

Date of Completion

January 2011

Keywords

Chemistry, Organic

Degree

Ph.D.

Abstract

Azobenzene undergoes reversible cis trans photoisomerization upon irradiation. Substituents often change the isomerization behavior of azobenzene, but not always in a predictive manner. We have synthesized several (aminomethylpyridine)azobenzene (AzoAMP) derivatives with unusual optical properties. These AzoAMPs exhibit minimal trans cis photoisomerization, extremely rapid cistrans thermal recovery and enhanced fluorescence emission. Computational and x-ray crystallographic data indicate intramolecular hydrogen bonding and electronic effects of substituents are responsible for the unusual behavior of AzoAMPs. Confirmation that AzoAMPs retain excited state photochemistry analogous to azobenzene was provided by ultrafast transient absorption spectroscopy. Photoactivity of AzoAMPs can be restored by chemical modification of functional groups and substituents. Our findings indicate the preferred mechanism for isomerization of AzoAMPs to be concerted-inversion. ^ Caged complexes are metal ion chelators that release analytes when exposed to light of a specific wavelength. We are interested in designing and synthesizing cages for Zn2+ that fragments upon photolysis. The general uncaging strategy involves integrating a nitrobenzyl group on the backbone of a ligand so that a carbon-heteroatom bond is cleaved following illumination. Several caged complexes (ZinCleavs) were obtained using a new synthetic strategy involving a Strecker synthesis to prepare a key aldehyde intermediate. The ability of ZinCleavs to increase free [Zn2+] was demonstrated practically by using fluorescent sensors to image the liberated Zn 2+. Dissociation constant and quantum yield measurements indicate ZinCleavs are capable of perturbing zinc homeostasis in live cells under experimental conditions. Free Zn2+ may function as a neurotransmitter and have a role in the pathology of several neurological diseases. Studying these physiological functions remains challenging because Zn2+ is silent to most common spectroscopic techniques. ZinCleavs are the first cages reported for Zn2+ and will facilitate biological investigations. ^