This paper presents a comprehensive review of the literature on one-dimensional (1D) nanostructures (nanowires, nanoribbons, nanotubes, nanobelts, and nanofibers) of π-conjugated small molecules, oligomers, and polymers. The diverse methods used in assembling the molecular building blocks into 1D functional nanostructures and nanodevices are discussed, including hard and soft template-assisted synthesis, electrospinning, nanolithography, self-assembly in solution and at interfaces, physical vapor transport, and other strategies. Optical, charge transport, electronic, and photoconductive properties of nanowires and nanotubes of selected classes of π-conjugated molecular systems are discussed next, highlighting unique features of the 1D nanostructures compared to 2D thin films. Overview of applications of these 1D organic nanostructures ranging from nanoscale light-emitting diodes, field-emission devices, organic photovoltaics, sensors/biosensors, spin-electronics, and nanophotonics to nanoelectronics is then given. The final section provides our brief concluding comments on the status of the field and on areas of outstanding challenges and opportunities for future work. We believe that the emerging confluence of nanoscience and organic semiconductors will greatly enrich both fields while leading to enhanced performance in organic electronics and affordable nanotechnologies.

New electron-acceptor materials are long sought to overcome the small photovoltage, high-cost, poor photochemical stability, and other limitations of fullerene-based organic photovoltaics. However, all known nonfullerene acceptors have so far shown inferior photovoltaic properties compared to fullerene benchmark [6,6]-phenyl-C60-butyric acid methyl ester (PC60BM), and there are as yet no established design principles for realizing improved materials. Herein we report a design strategy that has produced a novel multichromophoric, large size, nonplanar three-dimensional (3D) organic molecule, DBFI-T, whose π-conjugated framework occupies space comparable to an aggregate of 9 [C60]-fullerene molecules. Comparative studies of DBFI-T with its planar monomeric analogue (BFI-P2) and PC60BM in bulk heterojunction (BHJ) solar cells, by using a common thiazolothiazole-dithienosilole copolymer donor (PSEHTT), showed that DBFI-T has superior charge photogeneration and photovoltaic properties; PSEHTT:DBFI-T solar cells combined a high short-circuit current (10.14 mA/cm(2)) with a high open-circuit voltage (0.86 V) to give a power conversion efficiency of 5.0%. The external quantum efficiency spectrum of PSEHTT:DBFI-T devices had peaks of 60-65% in the 380-620 nm range, demonstrating that both hole transfer from photoexcited DBFI-T to PSEHTT and electron transfer from photoexcited PSEHTT to DBFI-T contribute substantially to charge photogeneration. The superior charge photogeneration and electron-accepting properties of DBFI-T were further confirmed by independent Xenon-flash time-resolved microwave conductivity measurements, which correctly predict the relative magnitudes of the conversion efficiencies of the BHJ solar cells: PSEHTT:DBFI-T > PSEHTT:PC60BM > PSEHTT:BFI-P2. The results demonstrate that the large size, multichromophoric, nonplanar 3D molecular design is a promising approach to more efficient organic photovoltaic materials.

Conjugated polymer systems, including homopolymers, 1 alternating/random copolymers, 2 blends, 3 and block copolymers, 4,5 as semiconductors for electronic and optoelectronic applications are of continuing great interest. 6,7 In general, multicomponent conjugated polymer systems such as blends and block copolymers offer the opportunity to optimize and tailor electronic and optical properties while also having the potential to observe novel phenomena (e.g., energy transfer, charge transfer) not feasible in homopolymers and random/alternating copolymers.5 Compared to blends, 3 block copolymers are of special interest because of their superior self-assembly features and the improved control of the nanoscale domain sizes of their assembled structures. Indeed, the synthesis, self-assembly, and properties of rod-coil block copolymers, having a π-conjugated (rodlike) block and a coillike nonconjugated block, have been extensively studied. 4 Although experimental examples of allconjugated block copolymers have been known since 1996, 5a their synthesis, solution-phase self-assembly, melt-phase selfassembly, and properties remain to be fully investigated. 5,8 Recently, block copolythiophenes with crystalline-amorphous diblock architecture incorporating a crystalline poly(3-hexylthiophene) (P3HT) block were successfully synthesized by quasiliving chain growth polymerization, including poly{3-[2-(2-methoxyethoxy)ethoxy]methylthiophene}, 8b poly[3-(2-ethylhexylthiophene)], 8c or poly(3-phenoxymethylthiophene) 8d as the amorphous segment. The thin-film morphology of these crystalline-amorphous diblock copolythiophenes was shown by atomic force microscopy (AFM) to be microphase-separated into crystalline and amorphous domains. For many electronic and optoelectronic applications such as field-effect transistors and photovoltaic devices, where high carrier mobilities and high absorption coefficients are important, 6,7 amorphous domains are undesirable. We report herein the synthesis and self-assembly of crystalline-crystalline diblock copoly(3-alkylthiophene)s. Two compositions of the new regioregular poly(3-butylthiophene)-b-poly(3-octylthiophene) (P3BT-b-P3OT) were found to self-assemble into crystalline nanowires in solution and shown by wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS) to be microphase-separated from the melt phase into two distinct crystalline domains with a lamellar structure.The synthesis of the diblock copoly(3-alkylthiophene)s was carried out by a modified Grignard metathesis method (GRIM), 1b,8 as illustrated in Scheme 1. The P3OT block was first synthesized by polymerization of 2,5-dibromo-3-octylthiophene, followed by the addition of activated 2,5-dibromo-3-butylthiophene monomer solution, giving the diblock copolymer system, poly(3-butylthiophene)-b-poly(3-octylthiophene). Two compositions, denoted BO50 and BO76, were synthesized by using the feed ratios of 2,5-dibromo-3-octylthiophene to 2,5-dibromo-3-butylthiophene of 1:1 and 1:2, respectively. The actual compositions...

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We report the synthesis, characterization, solution-phase assembly of nanowires, field-effect charge transport, and photovoltaic properties of regioregular poly(3-pentylthiophene) (P3PT), the first regioregular poly(3-alkylthiophene) with an odd-numbered alkyl side chain length to be so investigated. Two samples of P3PT with weight-average molecular weights of 61 800 and 77 000 and 1.4−1.5 polydispersity index have comparable solubility and processability in organic solvents as regioregular poly(3-hexylthiophene) (P3HT) but have a higher melting transition at 259 °C. X-ray diffraction of P3PT films revealed a lamellar structure with an interlayer d 100 spacing of 1.51 nm and a π-stacking d 010 spacing of 0.374 nm, both smaller than in P3HT. Crystalline nanowires of 16−17 nm width and aspect ratios as high as 465 were assembled from P3PT solution. Field-effect transistors fabricated from P3PT thin films showed a mobility of holes of up to 0.10 cm2/(V s), and the carrier mobility increased with molecular weight. Bulk heterojunction solar cells based on P3PT/fullerene (PC71BM) blend thin films had a power conversion efficiency of 3.70% under 100 mW/cm2 AM1.5 solar illumination in air and a maximum external quantum efficiency of 69%. Similarly illuminated solar cells based on nanocomposites of P3PT nanowires/PC71BM had a 3.33% power conversion efficiency. These results demonstrate that P3PT is an attractive polymer semiconductor suitable for applications in thin-film and nanowire-based field-effect transistors and bulk heterojunction solar cells.