Polythiophene Nanoparticles

Molecular self-organization in solution depends critically on molecular structural features and on concentration. Molecular self-organization or aggregation in solution occurs at the critical saturation concentration when the solvency of the medium is reduced. This can be achieved by solvent evaporation, reduced temperature, addition of a nonsolvent, or a combination of all these factors. Solvato-chromism and thermochromism of conjugated polymers such as regioregular polythiophenes are two illustrative examples, respectively, of solubility and temperature effects [43-45]. It should therefore be possible to use these solution phenomena to pre-establish desirable molecular organization in the semiconductor materials before deposition. Our studies of the molecular self-assembly behavior of PQT-12, which leads to the preparation of structurally ordered semiconductor nanopartides [46], will be described. These PQT-12 nanopartides have consistently provided excellent FETcharacteristics for solution-processed OTFTs, irrespective of deposition methods. 

In hot, dilute dichlorobenzene solutions ( 50 °C) broad absorption at Amax 480 nm is apparent in the UV-visible spectrum of PQT-12 (Fig. 4.8a), but the absorption is slightly red-shifted with the concomitant appearance of weak absorption at A max 610 nm (Fig. 4.8b) when the solution is cooled to room temperature. This is obviously because of the migration of PQT-12 molecules from the twisted disordered conformation in hot solution to an ordered coplanar conformation at lower temperatures. Because the HOMO level of PQT-12 in the solid state, esti- 

Upon annealing at 145 °C, the NanoPQT thin film gives an XRD diffraction pattern (Fig. 4.9d) which is similar to that from an annealed thin film from the hot solution (Fig. 4.6d). The interchain distance tightens to 17.2 A (28 = 5.T), accompanied by the disappearance of 28 = 7.4° and 22.1° diffraction peaks associated with the side-chain interlayer and n-n stacking respectively. The disappearance of these diffraction peaks is indicative of the preferential orientation of PQT-12 lamellar structures with their (100) axes normal to the substrate - a result of the interaction of PQT-12 dodecyl side-chains with the octyl chains of the OTS-8 modified surface induced and facilitated by thermal annealing. 

NanoPQT dispersion, with n-n stacking reflection (d) XRD of annealed PQT-12 film, with reflections for interchain ordering only at 26= 5.1°, 10.1°, 15.2° (e) electron micrograph of annealed film showing n-n stack reflection and (f) schematic representation of PQT-12 lamellar n-n stacking structure [46]. 

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Ong, B.S. et al.. Structurally ordered polythiophene nanoparticles for high-performance organic thin-fihn transistors, Adv. Mater. 17, 1141, 2005. 

Keywords Thermoelectric power, Seebeck coefficient, thermal conductivity electrical conductivity power factor, figure of merit, intrinsically conducting polymers, polyaniline, polypyrrole, polythiophene, nanoparticles, graphene, carbon nanotubes (CNTs), hybrids, nanocomposites... 

Gnanakan, S. R. R Murugananthem, N. Subramania, A. Organic acid doped polythiophene nanoparticles as electrode material for redox supercapacitors. Polymer Adv. Tech. 2011,22,788-793. 

Guan H, Zhou P, Zho X, He Z (2008) Sensitive and selective detection of aspartic acid and glutamic acid based on polythiophene-gold nanoparticles composite. Talanta 77 319-324... 

Polythiophenes and MEH-PPV have been used as hole-transporting layers to replace the electrolyte in cells with TiC>2 electrodes (Gratzel cells). Bulk hetero-junction devices have been made by the hydrolysis in air of titanium(IV) wopropoxide, co-deposited in MDMO-PPV spin-coated films, to form TiC>2 nanoparticles (van Hal et al., 2003). While reasonable peak performance under monochromatic illumination has been reported, the performance as a solar cell does not match that of the photo-electrochemical cells. 

Different electron-conducting polymers (polyaniline, polypyrrole, polythiophene) are considered as convenient substrates for the electrodeposition of highly dispersed metal electrocatalysts. The preparation and the characterization of electronconducting polymers modified by noble metal nanoparticles are first discussed. Then, their catalytic activities are presented for many important electrochemical reactions related to fuel cells oxygen reduction, hydrogen oxidation, oxidation of Cl molecules (formic acid, formaldehyde, methanol, carbon monoxide), and electrooxidation of alcohols and polyols. 

V. Selvaraj and M. Alagar, Ethylene glycol oxidation on Pt and Pt-Ru nanoparticle decorated polythiophene/multiwaUed carbon nanotube composites for fuel cell applications. Nanotechnology, 19, 045504 (2008). 

L. Zhai and R. D. McCullough, Regioregular polythiophene/gold nanoparticle hybrid materials. J. Mat Chem., 14, 141-143 (2004). 

Figure 12.20 TEM image of coie-sheU particle. TiOj nanoparticle with polythiophene shell. The transition from the crystalline TiOj to the amorphous polythiophene is shown. Shell thickness is 4 nm.

W. Beek, M. Wienk, and R. Janssen, Hybrid solar cells from regioregular polythiophene and ZnO nanoparticles. Advanced Functional Materials,... 

R. C. Advincula, Hybrid organic-inorganic nanomaterials based on polythiophene dendronized nanoparticles, Dalton Trans., 2778-2784 (2006). 

Zotti G, Vercelli B, Berlin A (2008) Gold nanoparticle linking to polypyirole and polythiophene monolayers and multilayers. Chem Mater 20 6509-6516... 

Wang S, Li C, Chen F, Shi G (2007) Layer-by-layer deposited multilayer films of water soluble polythiophene derivative and gold nanoparticles exhibiting photoresponsive properties. Nanotechnology 18 185707(1)-185707(6)... 

Panda BR, Chattopadhyay AJ (2007) A water-soluble polythiophene-Au nanoparticle composite for pH sensing. Colloid Interf Sci 316 962-967... 

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