Observation of magneto-electric rectification at non-relativistic intensities.

The subject of electromagnetism has often been called electrodynamics to emphasize the dominance of the electric field in dynamic light-matter interactions that take place under non-relativistic conditions. Here we show experimentally that the often neglected optical magnetic field can nevertheless play an important role in a class of optical nonlinearities driven by both the electric and magnetic components of light at modest (non-relativistic) intensities. We specifically report the observation of magneto-electric rectification, a previously unexplored nonlinearity at the molecular level which has important potential for energy conversion, ultrafast switching, nano-photonics, and nonlinear optics. Our experiments were carried out in nanocrystalline pentacene thin films possessing spatial inversion symmetry that prohibited second-order, all-electric nonlinearities but allowed magneto-electric rectification.

Alignment of Lyotropic Liquid Crystalline Conjugated Polymers in Floating Films.

Directed alignment of polymer chains plays an indispensable role in charge transport properties. We focus not only on a specific method to induce the alignment but also on the design of a liquid crystalline (LC) conjugated polymer to take advantage of an intrinsic self-assembly characteristic. We synthesized a lyotropic LC conjugated polymer, CP1-P, having o-nitrobenzyl (ONB) esters as photocleavable side chains and adopted a floating film transfer method to induce the polymer chain alignment through a lyotropic LC phase transition. An optimum amount of a high boiling point solvent (1,2-dichlorobenzene) in chloroform turned out to be an important factor to maximize the polymer chain alignment. The hole transport mobility along the polymer chain alignment direction was 13-14 times higher than that in the direction perpendicular to the alignment. In addition, the removal of side chains resulted in the solvent resistivity while maintaining the alignment feature in organic thin-film transistors.

A Novel Mechanism for Chemical Sensing Based on Solvent-Fluorophore-Substrate Interaction: Highly Selective Alcohol and Water Sensor with Large Fluorescence Signal Contrast.

Differentiation of solvents having similar physicochemical properties, such as ethanol and methanol, is an important issue of interest. However, without performing chemical analyses, discrimination between methanol and ethanol is highly challenging due to their similarity in chemical structure as well as properties. Here, we present a novel type of alcohol and water sensor based on the subtle differences in interaction among solvent analytes, fluorescent organic molecules, and a mesoporous silica gel substrate. A gradual change in the chemical structure of the fluorescent diketopyrrolopyrrole (DPP) derivatives alters their interaction with the substrate and solvent analyte, which creates a distinct intermolecular aggregation of the DPP derivatives on the silica gel substrate depending on the solvent environment and produces a change in the fluorescence color and intensity as a sensory signal. The devised sensor device, which is fabricated with simple drop-casting of the DPP derivative solutions onto a silica gel substrate, exhibited a completely reversible fluorescence signal change with large fluorescence signal contrast, which allows selective solvent detection by simple optical observation with the naked eye under UV light. Superior selectivity of the alcohol and water sensor system, which can clearly distinguish among ethanol, methanol, ethylene glycol, and water, is demonstrated.

High-Performing Thin-Film Transistors in Large Spherulites of Conjugated Polymer Formed by Epitaxial Growth on Removable Organic Crystalline Templates.

Diketopyrrolopyrrole (DPP)-based conjugated polymer PDTDPPQT was synthesized and was used to perform epitaxial polymer crystal growth on removable 1,3,5-trichlorobenzene crystallite templates. A thin-film transistor (TFT) was successfully fabricated in well-grown large spherulites of PDTDPPQT. The charge carrier mobility along the radial direction of the spherulites was measured to be 5.46-12.04 cm(2) V(-1) s(-1), which is significantly higher than that in the direction perpendicular to the radial direction. The dynamic response of charge transport was also investigated by applying a pulsed bias to TFTs loaded with a resistor (∼20 MΩ). The charge-transport behaviors along the radial direction and perpendicular to the radial direction were investigated by static and dynamic experiments through a resistor-loaded (RL) inverter. The RL inverter made of PDTDPPQT-based TFT operates well, maintaining a fairly high switching voltage ratio (Vout(ON)/Vout(OFF)) at a relatively high frequency when the source-drain electrodes are aligned parallel to the radial direction.

High aspect ratio conjugated polymer nanowires for high performance field-effect transistors and phototransistors.

We synthesized a highly crystalline DPP-based polymer, DPPBTSPE, which contained 1,2-bis(5-(thiophen-2-yl)selenophen-2-yl)ethene as a planar and rigid electron donating group. High- and low-molecular weight (MW) DPPBTSPE fractions were collected by Soxhlet extraction and were employed to investigate their unique charge transport properties in macroscopic films and single crystalline polymer nanowire (SC-PNW), respectively. The low-MW polymer could provide well-isolated and high aspect ratio SC-PNWs, in which the direction of π-π stacking was perpendicular to the wire growing axis. The field effect transistors made of SC-PNWs exhibited remarkably high carrier mobility of 24 cm(2) V(-1) s(-1). In addition, phototransistors (PTs) made of SC-PNW showed very high performance in terms of photoresponsivity (R) and photoswitching ratio (P). The average R of the SC PNW-based PTs were in the range of 160-170 A W(-1) and the maximum R was measured at 1920 A W(-1), which is almost three orders higher than that of thin film-based PT device.

Diketopyrrolopyrrole-bitellurophene containing a conjugated polymer and its high performance thin-film transistor sensor for bromine detection.

A new bitellurophene-based π-conjugated polymer (PDPPBTe) was synthesized and its semiconducting property was utilized for detecting Br2. The PDPPBTe polymer exhibited a highly sensitive response to Br2, which was indicated by a significant variation of the drain current in thin-film transistors.

Novel polymer nanowire crystals of diketopyrrolopyrrole-based copolymer with excellent charge transport properties.

The first demonstration of polymer nanowire (PNW) crystals based on a diketopyrrolopyrrole-based copolymer (i.e., PDTTDPP), and their application to field-effect transistors (FETs) is reported. Remarkably, transmission electron microscopy and selected area electron diffraction analyses of the PNW reveal its single-crystalline (SC) nature. FETs fabricated of a SC PNW exhibit a maximal charge carrier mobility of ≈7.00 cm(2) V(-1) s(-1) , which is almost one order of magnitude higher than that of the thin-film transistors made of the same polymer (PDTTDPP).

A novel tellurophene-containing conjugated polymer with a dithiophenyl diketopyrrolopyrrole unit for use in organic thin film transistors.

A new tellurophene-based π-conjugated polymer, PDTDPPTe, was synthesized. PDTDPPTe exhibits a smaller optical band gap (E(g)(opt) = 1.25 eV) than thiophene-based PDTDPPT (E(g)(opt) = 1.30 eV). Thin-film transistors comprising PDTDPPTe displayed outstanding performance (µ(max) = 1.78 cm(2) V(-1) s(-1), I(on)/I(off) = 10(5-6)).