Department of Chemistry

• Awards & Honors
  • Visiting Scientist at Los Alamos National Laboratory, 1983-84, 1995-96, 2009

Photochemistry and Photophysics of Transition Metal Complexes

Molecules excited by light lose energy by emission of light, transfer of energy or an electron to other molecules, photochemistry, and non-destructive radiationless processes. Solar energy conversion, chemical analysis, and light intensity measurements require information from the study of these processes. The processes can be highly sensitive to environmental factors such as solvent and interactions with organized media such as micelles, cyclodextrins, membranes, proteins, and DNAs. In addition, luminescence properties are very sensitive to the environment in polymer-supported sensors. We are elucidating the nature of these processes, correlating properties with molecular structure and environment, and developing new chemical, instrumental, and mathematical tools for studying these processes.

Our work includes:

• Design, synthesis and characterization of highly luminescent Os, Ir, Re, and Ru complexes.
• Evaluating photochemical properties, excited state ordering, and paths of energy loss.
• Fundamental and applied studies of interactions of photosensitizers with polymers, micelles, membranes and other organized media.
• Developing new luminescence-based sensors (e.g., oxygen, pH, metal ion).
• Design and utilization of metal complexes as probes of the structure and dynamics of organized media such as DNAs and membranes.
• Instrumental and theoretical developments in ultrasensitive, multicomponent fluorometric analyses.

An example of an analytical sensor is shown in the figure.

The photoluminescence of a tris(4,7-diphenyl-1,10-phenanthroline)ruthenium (II) complex in a polymer film is shown while the film is being breathed over. The luminescence is quite sensitive to deactivation by oxygen, and the luminescence intensity is a direct measure of the oxygen in the subject’s breath. Less oxygen yields more luminescence. The region immediately after the subject held his breath is revealing.

Recent Publications

Error propagation made easy – or at least easier. Gardenier GH, Gui F, Demas JN. J. Chem. Ed. 88, 916-20 (2011).

Luminescence oxygen sensor based on a ruthenium(II) star polymer complex. Payne SJ, Fiore GL, Fraser CL, Demas JN. Anal Chem. 82:917-21 (2010).

Abnormal behavior in Stern-Volmer luminescence quenching measurements via apparent lifetime methods. Payne SJ, Demas JN, Degraff BA. Appl Spectrosc. 63, 437-41 (2009).

Measuring proton diffusion in pH sensor films by lifetimes of luminescent complexes measured in the frequency domain. Bowyer WJ, Xu W, Demas JN. Anal. Chem. 81, 378-84 (2009).

Luminescence lifetime standards for the nanosecond to microsecond range and oxygen quenching of ruthenium (II) complexes. Morris K, Roach M, Xu W, Demas JN, DeGraff BA.  Anal. Chem. 79, 9310-14.

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