Reactivity of radical ions and radicals; electron transfer; molecular
electronic devices; synthesis of theoretically interesting molecules;
design of molecular catalysts.
Physical Organic Chemistry
primary research interests of this group are in the chemistry of
open-shell species, particularly radical ions. Studies are directed
toward deeper understanding of the influence of unpaired spin on
reactivity patterns. The group is interested in the development of
basic principles of interaction of an unpaired spin with paired
electrons in the same molecule, as well as in intramolecular
electron-transfer reactions. An understanding of elementary chemical
processes involving odd electron species, such as unimolecular
dissociation or electron transfer, is important not only for its
intrinsic value but also because it is applicable in numerous other
fields (e.g., organic synthesis, biological electron transfer,
catalysis, light-energy conversion, and electronic molecular devices).
The major goal of this investigation is to quantify
the relation between thermodynamics and kinetics of unimolecular
fragmentation reactions of radical ions (mesolytic cleavages, Figure 1).
This study includes probing ion pairing and solvent effects, as well as
a search for an inverted region for highly exergonic processes. The
data obtained provide a starting point for a unifying theoretical
treatment of unimolecular dissociation reactions in solution. This
research is currently being expanded to include other types of organic
reactions. The kinetic and thermodynamic contributions to
nucleophilicity and solvation effects are dissected.
In a related area, charge-transfer interactions are
investigated in the context of the generation of radical ions. In this
project the light energy is used to overcome the thermodynamic barrier
associated with electron removal or attachment. Investigations in this
area aim at an understanding of elementary reactions involved in such
ET processes, with emphasis on the dynamics of ion pairs produced in
these reactions. The specific goal is to explore factors controlling
overall efficiency of photo-driven mesolytic reactions, including the
effects of energetics of back electron transfer (BET) and bond
scission, and the spin and solvation status of produced ions. The
charge-transfer interactions are also used as a tool to probe
intermolecular interactions contributing to molecular recognition. Such
studies are currently being extended to include aqueous environment.
Another project concentrates on delocalization of electrons in three-dimensional networks of spiroconjugated compounds (Figure 2).
These studies include synthesis of new spiroconjugated systems with
novel electronic properties (three-dimensional donors and acceptors),
interesting optical properties (intramolecular charge-transfer dyes),
and magnetic properties (high-spin spiroconjugated diradicals). The
emphasis of this research is on preparation on new materials capable of
Other studies are concerned with near
diffusion-limited reactions of reactive intermediates. The solvent-cage
effects are probed by simple techniques based on competition
experiments. For example, one project involves investigation of
phosphoryl nitrenes as potential photoaffinity labeling reagents for
use in studies of receptors and binding sites of bioactive molecules.