Faculty & Research > Faculty > James N. Demas

demas

James N. Demas

Professor of Chemistry

jnd@virginia.edu
Room 144, Chemistry Building (434) 924-3343

Demas Group Website

B.S. University of New Mexico, 1964

Ph.D. University of New Mexico, 1970

National Science Foundation Postdoctoral Fellow,
University of Southern California, 1970-71

Photochemistry and Photophysics of Transition Metal Complexes

Professor Demas is not currently accepting graduate students.

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.demas-graph

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

Aromatic difluoroboron β-diketonate complexes: effects of π-conjugation and media on optical properties. Xu S, Evans RE, Liu T, Zhang G, Demas JN, Trindle CO, Fraser CL. Inorg Chem. 52:3597-610 (2013).

Viscosity and temperature effects on the rate of oxygen quenching of tris-(2,2′-bipyridine)ruthenium(II). Reynolds EW, Demas JN, DeGraff BA. J Fluoresc. 23:237-41 (2013).

Environmental sensitivity of Ru(II) complexes: the role of the accessory ligands. Dixon EN, Snow MZ, Bon JL, Whitehurst AM, DeGraff BA, Trindle C, Demas JN. Inorg Chem. 51:3355-65 (2012).

Photophysical and analyte sensing properties of cyclometalated Ir(III) complexes. Leavens BB, Trindle CO, Sabat M, Altun Z, Demas JN, DeGraff BA. J Fluoresc. 22:163-74 (2012).

Laser phosphoroscope and applications to room-temperature phosphorescence. Payne SJ, Zhang G, Demas JN, Fraser CL, Degraff BA. Appl Spectrosc. 65:1321-4 (2011).

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