1. Organic Semiconductor Nanowires: 1D Enhanced Optoelectronic Properties & Applications in Vapor Sensing Ling Zang, USTAR Prof. Department of Materials Science and Engineering Director, Utah Center of Trace Explosives Detection (UCTED) www.eng.utah.edu/~lzang

2. 1D self-assembly through solution or surface processing Zang et al. Accounts of Chemical Research, 2008, Special Issue on Nanoscience, vol. 41, pp1596-1608.

4. Easy to modify: chemical interactions.

5. Flexible for processing: vapor, liquid/solution, solid.

6. Adaptable to various substrate.

7. Cheap for manufacturing, processing, packaging.

9. Integrated for multi-target detection

10. Linearly polarized emission : single-nanobelt study by NSOM J. Phys. Chem. B, 110 (2006), 12327-12332

11. Waveguide:just another 1D confinement Chem. Mater. 21(2009) 2930-34.

12. Waveguide:just another 1D confinement Chem. Mater. 21(2009) 2930-34.

13. Self-waveguide emission: dominated by exciton migration at elevated temperature 300 K 4 K Lupton, Zang, et al. Nano. Lett. 11 (2011) 488-492.

14. Thermo-enhanced exciton diffusion Waveguiding dominated Lupton, Zang, et al. Nano. Lett. 11 (2011) 488-492.

15. Fluorescence emission illumination X Fluorescence emission Fluorescence emission illumination illumination TNT * * * * * Charge transfer occurs between the Excited state (exciton) and TNT Nanofiber: enhanced fluorescence sensing Long-range exciton migration enables amplification of fluorescence quenching: locally formed excited state can be quenched by an explosive molecule randomly adsorbed on surface.

17. Continuous porosity  expedient diffusion of gaseous molecules;

18. Large surface area  increased adsorption.Zang et al. Accounts of Chemical Research, 2008, Special Issue on Nanoscience, invited.

19. Efficient fluorescence quenching upon exposure to TNT vapor 5 ppb detection limit, < 10 ppt J. Am. Chem. Soc.129 (2007) 6978-6979

20. Quenching efficiency independent on film thickness--- easy for manufacturing Long-range exciton migration + Cross-film diffusion of explosives Thickness independence J. Am. Chem. Soc.129 (2007) 6978-6979

21. Efficient fluorescence sensing of amines vapor amine Nano Lett.,8 (2008) 2219-2223

22. Maximal adsorption produces maximal sensing sensitivity

23. expedient diffusion of guest molecules fast sensing response: milliseconds continuous porosity Nano Lett.,8 (2008) 2219-2223

24. Tubular fibrils for enhanced vapor sampling and trapping

25. Emission intensity of tubular fibrils in response to TNT Emission quenching data from NRL vapor generator

26. Emission intensity of tubular fibrils in response to RDX Emission quenching data from NRL vapor generator

27. 1D enhancement of electrical conductivity via cofacial p-electronic delocalization of doped charges  Leading to a sensor for reducing reagents. J. Am. Chem. Soc.129 (2007) 6354-6355 and 129 (2007) 7234-7235.

28. Bare nanowire The conductivity estimated: 1.310-3 S m-1, about 1 order of magnitude higher than that measured from polymer nanowires, e.g., polythiophene, F8T2. The conductivity estimated: ca. 1.0 S m-1, about 3 order of magnitude higher than that of undoped silicon, 1.610-3 S m-1. Current enhancement upon exposure to hydrazine vapor e- amine J. Am. Chem. Soc.129 (2007) 6354-6355

29. Low conductivity for pristine organic semiconductor: neutral molecules, zero doping Long axis of nanowire zero charge carriers Photo-doping via D-A charge separation to enhance the conductivity J. Am. Chem. Soc. 132 (2010) 5743-5750.

30. Photo-doping of n-type nanowires via D-A charge separation Photoinduced ET Photoinduced ET electrons No ET Too fast Just right High conductivity: balance between intra- and inter-molecular ET. J. Am. Chem. Soc. 132 (2010) 5743-5750.

31. High 1D photo-conductivity 0.3 mW/mm2 0.03 On/off ratio > 1,000 @ low irradiation 0.4 mW/mm2 J. Am. Chem. Soc. 132 (2010) 5743-5750.

32. Vapor sensing through charge-carrier depletion Photoinduced ET electrons explosives Suited for sensing weak-oxidizing reagents that are difficult to detect by fluorescent sensors. J. Am. Chem. Soc. 132 (2010) 5743-5750.

33. Enhanced electrical vapor sensing via photo-doping Fast blowing of nitro-methane vapor volatile, weak-oxidizing, difficult to detect …

34. Ideal sensor for vapor detection High sensitivity or low detection limit: stand-off detection (> 50 m, ideally 100 m), trace TNT (40 ppt) over buried landmines. Fast response:seconds, porous structure and continuous channel both enhancing the penetration of gaseous molecules into the film, strong chemical interaction (sticking) at interface improving the accumulation of target molecules within the film. Stability: thermal damage, photobleaching, thick film desired for improved stability, sustainability, reliability and reproducibility. Selectivity: against environment interferences. Cost effective: cheap for materials and processing, flexible for materials modification and improvement, adaptable to various substrates for device fabrication --- all can be satisfied with organic materials. Easy to use, minimal maintenance, …

35. Thinner Fibers for Enhanced Vapor Sensing amine diameter 350 nm 40 nm ChemComm. 2009, p5106.

36. Enhanced Vapor Sensing of Aniline by shrinking down the size of fibers 40 nm nanofiber 350 nm nanofiber Detection limit down to a few ppt

38. TNT

39. TNT