NEWS OF THE WEEK PHOTONICS
MULTICOLORED INK POLYCHROMIC Photonic crystal device was developed by (from left) Ozin, graduate student Andre C. Arsenault, visiting physics professor Hernan MigueZp postdoc Vladimir Kitaev, and Manners.
Color of nanocomposite colloidal crystal is solvent and redox tunable
A
REDOX-ACTIVE
SILICA-
polymer composite material may herald the development of a new kind of digital display technology, according to scientists at the University of Toronto.
The material, dubbed photonic ink or p-ink, consists of planar arrays of silica microspheres—an opal film—embedded in a matrix of cross-linked polyferrocenylsilane (PFS). The composite is a colloidal crystal that swells and shrinks reversibly in response to a solvent or redox change. It was prepared by chemistry professors Geoffrey A. Ozin and Ian Man-
JOURNAL
ners and coworkers {Adv. Mater., 15,503(2003)]. "The ultimate idea is to put the film of the material and a solvent onto an electrode and deliver different amounts of charge to the matrix so that the polymer will expand or contract accordingly," Manners tells C & E N . "With electrodes, it should be possible to pixelate and change the color of individual pixels." Ozin says the idea is "founded upon a specially designed metallopolymer-silica colloidal crystal nanocomposite film whose lattice dimensions are tunable by the application of a solvent or by a charge change to the film. Light incident on the film is optically Bragg diffracted at a wavelength related to the lattice dimensions of the film and is, in principle, continuously tunable across the entire visible spectral range." The optical response of the film to a change in solvent is exceptionally fast, according to the authors. It switches from the dry shrunken state to a fully swollen
state in less than half a second. Each repeat unit of PFS contains a redox-active ferrocene group. In a solvent, the PFS-opal composite gel contracts on oxidation since the polymer-solvent interactions are less favorable when the iron centers are oxidized. As a result, the Bragg diffraction shifts to a shorter wavelength. According to chemistry professor Thomas E. Mallouk at Pennsylvania State University, University Park, the electrochemical stop-band tuning reported in the paper is a clever piece of new science. Stop bands are photon band gaps that stop the passage of light only in certain crystal directions. "The dimensional and refractive index changes induced by redox cycling of the ferrocene polymer cause the stop band to be tunable between about 700 and 820 nm," he says. "Presumably, by using smaller spheres, the same kind of change could be made to happen in the visible." The team is now working to develop an electrochemical cell using the system. The aim is to incorporate the cell into prototype devices such as visible-light pixelated displays and near-infrared optical telecommunication switches and attenuators.— MICHAEL FREEMANTLE
PUBLISHING
Gordon Amidon Will Edit New ACS Journal, Molecular Pharmaceutics
T
he American Chemical Society announced this week that it will intro duce its 32nd journal, Molecular Pharmaceutics, early in 2004. Gordon L. Amidon, who is Charles R. Walgreen Jr. Professor of Pharmacy and professor of pharmaceutical sciences at the University of Michigan, Ann Arbor, will serve as editor of the new bimonthly. Amidon says the journal will concentrate on "the rapidly advancing molecular and mechanistic research in the pharma-
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ceutical and biopharmaceutical fields. The journal will have a distinct molecular and mechanistic focus emphasizing the chemistry of drug delivery." Possible subjects include drug and delivery system properties, drug transport and metabolism processes, and enzyme and transporter targets for drug delivery and targeting. John P. Ochs, director of new product development for ACS's Publications Division, says Amidon "has worked broadly in the chemical and chemical biological sciences in
drug delivery and has an extensive research background in molecular aspects of pharmaceutics and biopharmaceutics." Amidon earned a Ph.D. in pharmaceutical chemistry in 1971 from the University of Michigan. He was president of the American Association of Pharmaceutical Scientists in 1998 and is a fellow of the American Association for the Advancement of Science. He has served on editorial boards of numerous pharmaceutical journals. Amidon is chairman of drug delivery company PORT Systems and chairman and chief scientific officer of pharmaceutical product development firm TSRL—SOPHIE WILKINSON
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