Poly(oligothiophene-alt-benzothiadiazole)s: Tuning the Structures of Oligothlophene Units toward High-Mobility "Black" Conjugated Polymers

A series of donor-acceptor low-bandgap conjugated polymers, i.e., PTnBT (n = 2-6), composed of alternating oligothiophene (OTh) and 2,1,3-benzothiadiazole (BT) units were synthesized by Stille cross-coupling polymerization. The number of thiophene rings in OTh units, that is n, was tuned from 2 to 6. All these polymers display two absorption bands in both solutions and films with absorption maxima depending on n. From solution to film, absorption spectra of the polymers exhibit a noticeable red shift. Both high- and low-energy absorption bands or P'F5BT and PT6BT films locate in the visible region, which are at 468 and 662 nm for PT5BT and 494 and 657 nm for PT6BT.

The first liquid crystalline phthalocyanine derivative capable of edge-on alignment for solution processed organic thin-film transistors

Tetraoctyl-substituted vanadyl phthalocyanine (OVPc4C8) as a new NIR-absorbing discotic liquid crystalline material can form highly ordered thin films with edge-on alignment of the molecules and molecular packing mode identical to that in the phase II of OVPc for solution processed OTFTs with mobility up to 0.017 cm(2) V-1 s(-1).

Synthesis and properties of ferrocene-functionalised polythiophene derivatives

The ferrocene-functionalised thiophene derivatives (TFn) with different length of oxyethylene chains were synthesized and polymerized chemically with iron (III) chloride as an oxidant. The resulting ferrocene-functionalised polythiophenes (PTFn) show good solubility in most solvents, such as chloroform (CHCl3) tetrahydrofuran (THF), acetone, etc. The structure and properties of the PTFn polymers were confirmed by IR, H-1 NMR, AFM and photoluminescence (PL). The polymers PTFn show good redox activity with no attenuation of the electroactivity after multiple potential cycling. (C) 2009 Elsevier B.V. All rights reserved.

Effects of fullerene solubility on the crystallization of poly(3-hexylthiophene) and performance of photovoltaic devices

The substantial crystallization suppression of poly(3-hexylthiophene) (P3HT) in the untreated P3HT:C60 composite film prepared from o-dichlorobenzene (ODCB) solution has been revealed. Besides, the effective conjugation length of P3HT in this composite has been nearly maintained to that in the solution. The different crystallization behaviors of P3HT in its composites with C60 and [6,6]-phenyl C-61 butyric acid methyl ester (PCBM) are mainly attributed to the relative solubility of C60 and PCBM with respect to P3HT in ODCB. The solution to overcome this disadvantage of chain conformation and crystallinity of P3HT in the composite with C60 is thus proposed and finalized by resorting to the addition of low volatile solvent with much higher solubility of C60 than P3HT into the main solvent used, so as P3HT can crystallize before C60 forms crystallites in the solution. The feasibility of this approach has been proven by the improved efficiency of devices based on composites of P3HT and the low cost C60 without resorting to post-treatments.

Constructing Thin Polythiophene Film Composed of Aligned Lamellae via Controlled Solvent Vapor Treatment

Thin poly(3-butylthiophene) (P3BT) film composed of aligned lamellae attached to the edge of the original film has been achieved via a controlled solvent vapor treatment (C-SVT) method. The polarized optical microscopy operated at both single-polarization and cross-polarization modes has been used to investigate the alignment of the fiber-like lamellae. A numerical simulation method is used to quantitatively calculate angle distributions of the lamellae deviated from the film growth direction. Prepatterned P3BT film edge acts as nuclei which densely initialize subsequent crystal growth by exhausting the materials transported from the partially dissolved film. The growth of new film upon crystallization is actually a self-healing process where the two-dimensional geometric confinement is mainly responsible for this parallel alignment of P3BT crystals. The solvent vapor pressure should be carefully chosen so as to induce crystal growth but avoid liquid instability which will destroy the continuity of the film.

Rational Design, Synthesis, and Optical Properties of Film-Forming, Near-Infrared Absorbing, and Fluorescent Chiromophores with Multidonors and Large Heterocyclic Acceptors

A new series of film-forming, low-bandgap chromophores (1a,b and 2a,b) were rationally designed with aid of a computational study., and then synthesized and characterized. To realize absorption and emission above the 1000 nm wavelength, the molecular design focuses on lowering the LUMO level by fusing common heterocyclic units into a large conjugated core that acts an electron acceptor and increasing the charge transfer by attaching the multiple electron-donating groups at the appropriate positions of the acceptor core. The chromophores have bandgap levels of 1.27-0.71 eV, and accordingly absorb at 746-1003 nm and emit at 1035-1290 nm in solution. By design, the relatively high molecular weight (up to 2400 g mol(-1)) and non-coplanar structure allow these near-infrared (NIR) chromophores to be readily spin-coated as uniform thin films and doped with other organic semiconductors for potential device applications. Doping with [6,6]-phenyl-C-61 butyric acid methyl ester leads to a red shift in the absorption on]), for la and 2a. An interesting NIR electrochromism was found for 2a, with absorption being turned on at 1034 nm when electrochemically switched (at 1000 mV) from its neutral state to a radical cation state. Furthermore, a large Stokes shift (256-318 nm) is also unique for this multidonor-acceptor type of chromophore.

Why [6,6]- and 1,2-Benzal-3-N-4-O-Cyclic Phenylimidate C-60 Undergo Electrochemically Induced Retro-Addition Reactions while 1,4-Dibenzyl-2,3-Cyclic Phenylimidate C-60 Does Not? C-H center dot center dot center dot X (X = N, O) Intramolecular Interactions in Organofullerenes

The electrochemical properties of a series of structurally related fullerooxazoles, [6,6] cyclic phenylimidate C-60 (1), 1,2-benzal-3-N-4-O-cyclic phenylimidate C-60 (2), and 1,4-dibenzyl-2,3-cyclic phenylimidate C-60 (3), are described, and the spectroscopic characterizations of their anionic species are reported. The results show that compounds I and 2 undergo retro-cycloaddition reactions that lead to the formation of C-60 and C61HPh, respectively, upon two-electron-transfer reduction. However, compound 3 demonstrates much more electrochemical stability as no retro-cycloaddition reaction occurs under similar conditions. Natural bond orbital (NBO) calculations on charge distribution show there is no significant difference among the dianions of 1, 2, and 3, indicating that the electrochemical stability of 3 is unlikely to be caused by the charge distribution difference of the dianions of three compounds. Examination on the crystal structure of compound 3 reveals close contacts of the C-H group with the heteroatoms (N and O) of cyclic phenylimidate, suggesting the existence of C-H center dot center dot center dot X (X = N, O) intramolecular hydrogen bonding among the addends, which is further confirmed by NBO analysis.

Study on the Single Crystals of Poly(3-octylthiophene) Induced by Solvent-Vapor Annealing

Needle-like single crystals of poly(3-octylthiophene) (P3OT) have been prepared by tetrahydrofuran-vapor annealing. The morphology and structure of the crystals were characterized with optical microscopy, scanning electron microscopy, atomic force microscopy, transmission electron microscopy, and wide-angle X-ray diffraction. It is observed that the P3OT molecules are packed with the backbones parallel to the length axis of the crystal and the alkyl side chains perpendicular to the substrate. The field effect transistor based on the P3OT single crystal exhibited a charge carrier mobility of 1.54 x 10(-4) cm(2)/(Vs) and on/off current ratio of 37, and the molecular orientation of the crystal is ascribed to account for the device performance. The time-dependent morphological evolution demonstrated that the crystals underwent Ostwald ripening when annealed.

Achieving perpendicular alignment of rigid polythiophene backbones to the substrate by using solvent-vapor treatment

The rigid backbone of the poly(3-butylthiophene) molecule adopts a perpendicular orientation with respect to the substrate by using a solvent-vapor treatment (see figure). Small and closely contacting spherulites instead of conventional whisker-like crystals are achieved. This could be utilized to improve charge-carrier mobility particularly in the direction normal to the film plane by designing and constructing thick crystalline domains in the functional layer.

Enhanced electrical conductivity of highly crystalline polythiophene/insulating-polymer composite

Poly(3-butylthiophene) (P3BT)/insulating-polymer composites with high electrical conductivity have been prepared directly from the solution. These composites exhibit much higher conductivity compared to pure P3BT with the same preparation method provided that P3BT content is higher than 10 wt %. Morphological studies on both the pure P3BT and the composites with insulating polymer show that P3BT highly crystallizes and develops into whisker-like crystals. These nanowires are homogeneously distributed within the insulating polymer matrix and form conductive networks, which provide both extremely large interface area between conjugated polymer and insulating polymer matrix and highly efficient conductive channels through out the whole composite. In contrast, the conductivity enhancement of P3HT/PS composite is not so obvious and drops down immediately with increased PS content due mainly to the absence of highly crystalline whisker-like crystals and much larger scale phase separation between the components. The results presented here could further illuminate the origin of conductivity formation in organic semiconducting composites and promote applications of these polymer semiconductor/insulator composites in the fields of organic (opto-)electronics, electromagnetic shielding, and antistatic materials.

Studies on microstructure bilayer film of ultrasonic dipped cadmium sulfide and d.c. sputtered indium tin oxide

A bilayer CdS/ITO film was obtained. The dipped CdS was grown by an ultrasonic colloid deposition (USCD) method. Microstructure of the CdS film made by USCD has a wider transmission range and a higher transmittance. Amorphous indium-tin-oxide (ITO) thin film was deposited using d.c. magnetron-sputtering at room temperature. The ITO films exhibited good conductivity and maximum transmittance of 94%. The CdS/ITO bilayer was investigated by means of GIXD (grazing incidence X-ray diffraction) at different incidence angles (alpha = 0.20-5.00degrees) and XRD. We discuss a model for the thin bilayer film. SEM and AFM show that homogeneous CdS films with a bar-shaped ultrafine particles and ITO film with nanometer structure. The mechanism of the bilayer CdS/ITO film is discussed.

A room-temperature ionic-liquid-templated proton-conducting gelatinous electrolyte

Novel proton-conducting gelatinous electrolytes templated by room-temperature ionic liquid (RTIL) 1-butyl-3-methyl-imidazolium-tetrafluoroborate (BMImBF(4)) have been prepared in methylsisesquioxane backbone containing H3PO4, and the influences of the RTIL on the structure, morphology, thermal stability, and electrochemical properties of the gelatinous electrolytes have been examined. X-ray diffraction and scanning electron microscopy proved that BMImBF(4) acted as structure-directing template during the sol-gel process of methyl-trimethoxysilane. X-ray photoelectron spectra and infrared spectroscopy demonstrated that the hydrogen-bonding was formed between BMImBF(4) and H3PO4. The electrolytes had good thermal stability up to 300 degreesC and showed superior mechanical and electrochemical properties. A room-temperature conductivity of 1.2 x 10(-3) S cm(-1) was obtained for the electrolyte at the molar ratio of RTIL/Si/H3PO4 0.3/1/1, and its electrochemical window was up to 1.5 V.