J. Brooks, Florida State University, NSF DMR Making “plastics” do new things: Designer molecular crystals can: 2) be metals even without “doping” electrons into them. 1) switch from insulators to metals to insulators in very high magnetic fields. 3) conduct and store electrical charge when illuminated with light. e+e+ e-e- At low temperatures, very high magnetic fields induce dramatic electronic transitions in Perylene - based materials. High magnetic fields reveal the quantum motion of electrons and holes in strategically engineered single component molecular materials. Photons create electron- hole pairs in functionalized pentacene crystals – charges remain stable and mobile at low temperatures.

The purpose of the project "Electronic, Magnetic, and Thermodynamic Properties of Molecular Solids” is to use and to build upon our present understanding of the process by which electronic charge and spin can be introduced into non-conducting organic molecular crystals. The strategy, shown sequentially in items 1,2, and 3 above is to begin with molecular crystals where charge and/or spin is introduced through a normal donor-acceptor formula, but where the materials are at the frontier of this process. And from there, proceed to single component molecular systems where other charge and spin injection mechanisms are considered. The perylene system described in #1 is considered to be an almost perfect one dimensional conductor, but high magnetic fields show that there is an underlying exciting and very complex behavior. (D. Graf et al., Phys. Rev. Lett., in press 8/04) A second example in #2 above involves packing, through chemistry, insulating molecules so tightly that they are electrical conductors – high magnetic fields reveal their intrinsic metallic character through the observation of quantum oscillations of the conduction electrons. (H. Tanaka et al., JACS, in press 8/04) In #3 above pentacene functionalized with silyl side groups can be made to conduct current at low temperatures by inducing electron-hole states that are persistent, and can provide a conduction path as long as the sample is maintained at low temperatures (J.S. Brooks et al., J. Appl. Phys., in press 8/04). The solar cell on the next slide is an example of where fundamental research in this area can lead. Some other areas, not shown above include field induced superconductivity and field induced metal insulating states in two other magnetically-functionalized and highly engineered molecular systems (lambda-BETS2FeCl4 and tau-phase structures respectively). Another stated mission of the proposal is to explore these molecular systems on a reduced micro and nano-scale, where either light, magnetic field, or electric fields can change their physical properties, and results from this next stage of the proposal will soon be forthcoming.

REU Student David Lehr has successfully fabricated his first organic solar cell based on a functionalized pentacene/TCNQ thin film device. Lincoln High School Externs Kathy Goodman, Kelly Deuerlin, and Ryan Phelps watch the maiden voyage of their prototype magneto- hydrodynamic powered boat. Jeri Martin Amber Matthews Farrell Rogers RET’s use “jelly roll” capacitor to light an LED. REU student Charles Bosse makes the first pulsed field SdH measurement ever at the Tallahassee Lab. E D U C A T I O N A L OUTREACH