List of Faculty
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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:
(1) Design, synthesis and characterization of highly luminescent Os, Ir,
Re, and Ru complexes.
(2) Evaluating photochemical properties, excited state ordering, and paths
of energy loss.
(3) Fundamental and applied studies of interactions of photosensitizers with
polymers, micelles, membranes and other organized media.
(4) Developing new luminescence-based sensors (e.g., oxygen, pH, metal ion).
(5) Design and utilization of metal complexes as probes of the structure
and dynamics of organized media such as DNAs and membranes.
(6) 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. The emission is brightest on the first exhalation because of the extended exchange time in the lungs with a resultant reduction in the oxygen concentration. The equilibration of the lungs with continued breathing is clear. The initial irregularity is a consequence of the high carbon dioxide concentration in the blood stream.
We are also developing a number of sensing systems for pH, carbon dioxide, and metal ions. These systems are being applied to biomedical, industrial, and environmental monitoring.
Our methodologies include high sensitivity visible near infrared luminescence, nanosecond decay time measurements, flash photolysis, and time-resolved emission spectroscopy. In collaboration with the Keck Cellular Imaging Center, we are pioneering the use of fluorescence microscopy (conventional, two photon, and confocal) for understanding the interactions of polymers with sensor molecules. Under development are new ultra sensitive phase resolved luminescence methods for organic, biochemical, and inorganic analyses (e.g. uranium) and for the reduction of interferences.
Representative Publications
Potassium Ions Induced Changes of Crystal Structure and Luminescent Properties of a Fluorescent Crown Ether, Qiu-Xian Ren, Vincent Douglass, III, Wenying Xu, Michal Sabat. A. Periasamy, J. N. Demas, B. A. DeGraff, J. Fluor., 2005, in press.
Luminescence-Based Oxygen Sensors, B. A. DeGraff, J. N. Demas, Reviews in Fluorescence 2005, Volume 2, Eds. C. Geddes and J. R. Lakowicz, Springer Science, 125-151.
Luminescent Transition Metal Complexes as Sensors, Structural Effects on pH Response, Beradette Higgins, B. A. DeGraff, J. N. Demas, Inorg. Chem., 2005, 44, 6662-6669.
Determining Oxygen Diffusion Coefficients in Polymer Films by Lifetimes of Luminescent Complexes Measured in the Frequency Domain, Walter J. Bowyer, Wenying Xu, and J. N. Demas, Anal. Chem., 2004, 76, 4374-4378.
pH-Dependent Photophysical Behavior of Rhenium Complexes Containing Hydroxypyridine Ligands. William D. Bare, Nathan H. Mack, J. N. Demas, Appl. Spect., 2004, 58, 1093-1100.
Self-Referencing Intensity Measurements Based on Square Wave Gated Phase-Modulation Fluorimetry. H.M. Rowe, S.P. Chan, J.N. Demas, and B.A. DeGraff. Appl. Spect. 2003, 57, 532-537.
Photostability of Luminescent Ruthenium(II) Complexes in Polymers and in Solution. Z.J. Fuller, W.D. Bare, K.A. Kneas, J.N. Demas, and B.A. DeGraff. Anal. Chem. 2003. 75, 2670-2677.
Conventional, Confocal, and Two-Photon Fluorescence Microscopy Investigations of Polymer-Supported Oxygen Sensors. R.D. Bowman, K.A. Kneas, J.N. Demas, A. Periasamy. Microscopy and Microanalysis. 2002. 211, 112-120.
Multicomponent Lifetime-Based pH Sensors Utilizing Constant-Lifetime Probes. W.D. Bare, N.H. Mack, W. Xu, J.N. Demas, and B.A. DeGraff. Anal. Chem. 2002. 74, 2198-2209.
Simple Method for Measuring Oxygen Diffusion Coefficients of Polymer Films by Luminescence Quenching. K.A. Kneas, J.N. Demas, B. Nguyen, A. Lockhart, W. Xu, and B.A. DeGraff. Anal. Chem. 2002. 74, 1111-1118.
Single and Multiple Binding of β-Cyclodextrin and Polymeric β-Cyclodextrins to Luminescent Ruthenium(II) α-Diimine Complexes. W. Xu, A. Jain, B. A. Betts. J. Phys. Chem. A. 2002. 106: 251-257.
Applications of Luminescent Transition Platinum Group Metal Complexes to Sensor Technology and Molecular Probes. J.N. Demas, B.A. DeGraff. Coord. Chem. Rev. 2001. 211, 317-351.
Optimized Gating Scheme for Rapid Single Exponential Luminescence Lifetime Determinations. S.P. Chan, Z.J. Fuller, J.N. Demas, and B.A. DeGraff. Anal. Chem. 2001. 7, 4486-4490.
Lifetime Based pH Sensor System Based on a Polymer Supported Ruthenium(II) Complex. Y. Clark, W. Xu, J.N. Demas, B.A. DeGraff. Anal. Chem. 2000. 72, 3468-3475.
Fluorescence Microscopy Study of Heterogeneity in Polymer Supported, Luminescence Based Oxygen Sensors. K.K. Kneas, J.N. Demas, B.A. DeGraff, A. Periasamy. Microscopy and Microanalysis. 2000. 6, 551-561.
Oxygen Sensors Based on Luminescence Quenching. J.N. Demas, B.A. DeGraff, and P. Coleman. Anal. Chem. 1999. 71, 793A-800A.
Applications of Luminescent Transition Metal Complexes to Sensor Technology and Molecular Probes. J.N. Demas, B.A. DeGraff. J. Chem. Ed. 1997. 74, 690-695.
Oxygen Sensors Based on Luminescence Quenching, Interactions of Pyrene with the Polymer Supports. W. Xu, R. Schmidt, M. Whaley, J. N. Demas, B.A. DeGraff, E.K. Karikari, and B.L. Famer. Anal. Chem. 1995. 67, 3172-3180.
Long Lived, Highly Luminescent Rhenium(I) Complexes as Molecular Probes, Intra- and Intermolecular Excited State Interactions. L. Sacksteder, M. Lee, J.N. Demas, and B.A. DeGraff. J. Am. Chem. Soc. 1993. 115, 8230-8238.
Photophysics and Photochemistry of Oxygen Sensors Based on Luminescent Transition Metal Complexes. E.R. Carraway and J.N. Demas, B.A. DeGraff, and J.R. Bacon. Anal. Chem. 1991. 63, 337-342.
Design and Applications of Highly Luminescent Transition Metal Complexes. J.N. Demas and B.A. DeGraff. Anal. Chem. 1991. 63, 829A-837A.