No abstract

Stille coupling of regioisomerically pure dibromonaphthalene bisimides (NBI) with various stannylated thiophene-based monomers yields (very) high molecular weight donor-acceptor conjugated polymers. Electrochemical and optical absorption measurements reveal that LUMO energies are essentially invariant and dictated by the NBI units, while HOMO energies are dictated by the thienyl comonomers. Optical energy gaps ranging from 1.7 to 1.1 eV are thus obtained. The polymers are also characterized by differential scanning calorimetry and fiber WAXD.

Conjugated polymer actuators developed over the last decade have now reached the early stages of commercialization, particularly for use in biomedical devices, such as the blood vessel connector shown in the Figure. This article reviews the motivation for using this class of actuator, the types of devices that have been fabricated, and some of the biomedical applications that are being developed. Recommendations are also presented for future work. CommunicationsSubstituted hexabenzocoronenes (HBCs) form films with supramolecularly ordered columnar stacks that are uniaxially oriented onto poly(tetrafluoroethylene) alignment layers (see Figure). In field-effect transistor (FET) tests, mobilities of up to 10 ±3 cm 2 V ±1 s ±1and high on±off ratios of more than 10 4 were derived for these aligned HBC films, characteristics superior to FETs prepared from isotropic HBC layers.

The synthesis and characterization of two new thiophene copolymers with backbone phthalimide units is reported. Thin-film optical and wide-angle X-ray diffraction measurements indicate extended electronic conjugation and close intermolecular pi-stacking for both polymers. Ambient carrier mobility of thin-film transistors prepared from these polymers is as high as 0.28 cm(2)/(V s) with an on/off ratio greater than 10(5).

No abstract

A series of nine alternating donor–acceptor copolymer semiconductors based on naphthalene diimide (NDI) acceptor and seven different thiophene moieties with varied electron-donating strength and conformations has been synthesized, characterized, and used in n-channel and ambipolar organic field-effect transistors (OFETs). The NDI copolymers had moderate to high molecular weights, and most of them exhibited moderate crystallinity in thin films and fibers. The LUMO energy levels of the NDI copolymers, at −3.9 to −3.8 eV, were constant as the donor moiety was varied. However, the HOMO energy levels could be tuned over a wide range from −5.3 eV in P8 to −5.9 eV in P1 and P3. As semiconductors in n-channel OFETs with gold source/drain electrodes, the NDI copolymers exhibited good electron transport with maximum electron mobility of 0.07 cm2/(V s) in P5. Although head-to-head (HH) linkage induced backbone torsion, polymer P4 showed substantial electron mobility of 0.012 cm2/(V s) in bottom-gate/top-contact device geometry. Some of the copolymers with high-lying HOMO levels (P7 and P8) exhibited ambipolar charge transport in OFETs with high electron mobilities (0.006–0.02 cm2/(V s)) and significant hole mobilities (>10–3 cm2/(V s)). Varying the device geometry from top-contact to bottom-contact leads to the appearance or enhancement of hole transport in P4, P6, P7, and P8. Copolymers with smaller alkyl side chains on the imide group of NDI have enhanced carrier mobilities than those with bulkier alkyl side chains. These results show underlying structure–property relationships in NDI-based copolymer semiconductors while demonstrating their promise in n-channel and ambipolar transistors.

Uniaxially aligned, thin films of a discotic columnar thermotropic liquid crystalline material can be prepared by a simple solution zone-casting method, without the need for modified surfaces or traditional alignment techniques. Atomic force microscopy together with X-ray diffraction reveals single-crystalline-like order over several square centimeters, far exceeding the requirements for application of such films in organic molecular electronic devices such as field-effect transistors.

No abstract