This award in the Inorganic, Bioinorganic and Organometallic Chemistry program supports research by Professor Thomas G. Gray at Case Western Reserve University that emphasizes the organometallic chemistry and excited-state properties of gold(I). The leading objective is emplacement of gold(I) centers onto fluorescent organic molecules. The heavy-atom effect of gold opens access to the fluorophores' triplet-state photochemistry and photophysics. Gold can be introduced in sensitive, conjugated molecules that absorb at preordained wavelengths. Two new synthetic methods are demonstrated where gold(I) fragments are attached to aromatic skeletons through carbon-gold sigma bonds. The first of these, base-promoted transmetallation, binds gold to the peripheries of aromatic molecules and is broadly general and functionally tolerant. The second is a [3 + 2] cycloaddition reaction of gold(I) azides with terminal alkynes that yields gold(I) triazolato moieties. Photophysical studies, which include static and time- resolved emission measurements, demonstrate triplet-state luminescence from aromatics functionalized with gold. The synthesis concepts that underlie these activities permit measurement of both internal heavy-atom effects (through direct carbon-gold attachment) and of external effects, where gold is suspended above an emitting moiety upon a photoinert spacer.
A variety of day-to-day applications call for materials that are robust, tunable triplet-state emitters. Among these are light-emitting diode technology, photosensitization, and biological labeling. This research will also contribute to chemical pedagogy through the development of an undergraduate laboratory exercise in the synthesis and characterization of group 11 complexes of azadipyrromethene chromophores. This research is also training undergraduate and graduate students for scientific careers in industry, government, the military, and academia.
This award in Inorganic, Bioinorganic, and Organometallic Chemistry supported research in the chemistry of gold and the training of scientific professionals. Gold is too precious to be hoarded in bank vaults. This element is essential to electronics, catalysis, and organic synthesis. Gold is long used to alleviate rheumatoid arthritis and is drawing attention in the treatment of tropical diseases and cancer. Recent work shows that gold mediates chemical reactions that store solar energy. When bound to gold, molecules that had been fluorescent become phosphorescent, and gain long-lived excited states. Photochemical reactivity results. Intellectual Merits. NSF support has brought concepts in gold chemistry to fruition in the laboratory. Chemical reactions have been developed that attach gold to organic compounds in a pre-defined manner. The new processes are high-yielding. Stoichiometric and catalytic reactions were discovered that bind multiple gold atoms to the same carbon framework. The sensitive parts of intricate molecules survive intact when gold binds. Reliable reactions that form carbon-gold and nitrogen-gold bonds have been established. The light-emitting properties of gold organometallics, including excited-state lifetimes, have been measured. Rate constants of ultrafast processes in gold-bearing pyrenes have been reported. The first gold(I) complex of a porphyrin ligand was achieved; porphyrins are pigments that are important to light capture and essential to mammalian life. This unique gold(I) porphyrin complex was characterized by optical spectroscopy, and its solid-state structure was proven by X-ray crystallography. The new chemistry that led to this molecule extends to a variety of targets having gold-nitrogen bonds. Broader Impacts. NSF support has created a corpus of organometallic reactions that have easy applicability and wide use. Gold chemistry is now readily practiced by students, including undergraduates beginning their training. This project has sustained the professional formation of graduate and undergraduate students. It has supported Gray’s efforts to inaugurate a Bioinorganic Chemistry course that includes medicinal applications of gold compounds. Gray is a frequent lecturer in gold chemistry around the United States.
