Synthesis and Characterization of Fluorescent Acenequinones as Dyes for Guest-Host Liquid Crystal Displays Timothy M. Swager, Massachusetts Institute of Technology, DMR The synthesis of dichroic dyes is crucial for the development of fluorescent guest-host liquid crystal displays (GH-LCDs). We have prepared a series of linear para acenequinones, which demonstrated excellent alignment in the nematic liquid crystal host, with dichroic ratios of 8~10. The LC/dye mixtures also exhibited realignment under electric fields. hv strong emission weak emission liquid crystal dye Acenequinone Dye

2-D Shape Persistent Ladder Polymers: Synthesis and Contra- Aspect Ratio Alignment Timothy M. Swager, Massachusetts Institute of Technology, DMR A new class of polymeric materials produced that were shown by light scattering to exhibit a shape persistent 2-D disc structure. The structures are intrinsically non-compliant and the disc structures are effectively porous with high degrees of free volume. Conventional flexible polymers such as polyvinylchloride (PVC) thread through the pores and when stretched we demonstrate that the 2-D polymers align perpendicular to the direction of extension (Thomas, S. W.; Long, T. M.; Pate, B. D.; Kline, S. R.; Thomas, E. L.; Swager, T. M. J. Am. Chem. Soc. 2005, 127, ). This novel form of organization effectively results in a macromolecular object being aligned perpendicular to its aspect ratio. No other polymer systems have ever displayed this behavior and we hope to extend this to produce novel mechanical properties and effectively produce molecularly knitted structures. Electronic 0,0 Transition Is Short Axis Polarized Polarized Fluorescence from the Polyiptycene (M n =44K) Endgroups Show it to Align Normal to the Direction of PVC Alignment

Conjugated Polymers in an Arene Sandwich: Reducing Thin Film Sensitivity to Photobleaching Timothy M. Swager, Massachusetts Institute of Technology, DMR Our group has developed chemical and biological sensors based on fluorescent conjugated polymer thin films. For example, Nomadics, Inc. has commercialized one of our polymers for the sensitive detection of trinitrotoluene (TNT), a common explosive used in landmines. These sensors utilize an analyte-induced quenching of the polymer film’s fluorescence as a signal. A current major limitation is that the exposure to light induces an irreversible photobleaching of the polymer films, reducing both the fluorescence and sensitivity. Although the photobleaching mechanism is poorly understood, it is believed to be a bimolecular reaction between the photo-excited polymer and oxygen. Therefore, we have designed and synthesized polymers with a protective shell to limit O 2 access to the polymer backbone and thereby reduce the extent of photobleaching. Although we have successfully decreased the rate of photobleaching, further improvements are necessary and are currently in progress. New Polymers P1P2P3 Light Permanently Damages Films. Backbone Protection Photobleaching Rate Fluorescence Time (min) P3 P2 P1