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Koldemir U.,George and Josephine Butler Polymer Research Laboratory | Puniredd S.R.,Max Planck Institute for Polymer Research | Puniredd S.R.,Institute of Materials Research and Engineering of Singapore | Wagner M.,Max Planck Institute for Polymer Research | And 7 more authors.
Macromolecules | Year: 2015

Optimized microstructure through control of both intra- and intermolecular interactions in organic semiconductors is critical for enhancing and optimizing charge transport for the realization of next-generation low-cost, mechanically flexible, and easy to process high performance, organic field effect transistors (OFETs). Herein, we report donor-acceptor alternating copolymers of dithienogermole (DTG) with 2,1,3-benzothiadiazole (BTD) and probe the importance of end groups on the control of molecular order and microstructure as it relates to the enhancement of charge carrier transport. Partial end-capping reactions, confirmed by 1H NMR and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) analyses, on the DTG-BTD copolymer provided significant improvement in grazing incidence wide angle X-Ray scattering (GIWAXS) determined polymer ordering in thin films. Consequently, OFETs exhibited charge-carrier mobilities up to 0.60 cm2/(Vs) for the end-capped copolymer, which are an order of magnitude higher in comparison to the non-end-capped analogue, which displayed a mobility of 0.077 cm2/(Vs). We emphasize that a simple synthetic approach, the introduction of end-capping groups which remove reactive functionalities, can be effective in the development of next-generation OFET and solar materials by promising better control of the polymer organization. © 2015 American Chemical Society. Source


Deng C.C.,George and Josephine Butler Polymer Research Laboratory | Brooks W.L.A.,George and Josephine Butler Polymer Research Laboratory | Abboud K.A.,University of Florida | Sumerlin B.S.,George and Josephine Butler Polymer Research Laboratory
ACS Macro Letters | Year: 2015

This report describes the synthesis and characterization of boronate ester-cross-linked hydrogels capable of self-healing behavior at neutral and acidic pH. This atypically wide pH range over which healing behavior is observed was achieved through the use of an intramolecular coordinating boronic acid monomer, 2-acrylamidophenylboronic acid (2APBA), where the internal coordination helped to stabilize cross-links formed at acidic and neutral pH. Two different hydrogels were formed from a 2APBA copolymer cross-linked with either poly(vinyl alcohol) or a catechol-functionalized copolymer. The self-healing ability of these hydrogels was characterized through physical testing and rheological studies. Furthermore, the catechol cross-linked hydrogel was shown to be oxygen sensitive, demonstrating reduced self-healing and stress relaxation after partial oxidation. The synthesis of these hydrogels demonstrates a new strategy to produce boronic acid materials capable of self-healing at physiological pH. © 2015 American Chemical Society. Source


Stalder R.,George and Josephine Butler Polymer Research Laboratory | Mei J.,George and Josephine Butler Polymer Research Laboratory | Subbiah J.,University of Florida | Grand C.,George and Josephine Butler Polymer Research Laboratory | And 3 more authors.
Macromolecules | Year: 2011

The conjugated electron acceptor isoindigo was used to synthesize two conjugated polymers with backbones composed exclusively of electron-deficient units. Suzuki polycondensation afforded the homopolymer of isoindigo and a copolymer with 2,1,3-benzothiadiazole as repeat unit. The materials are thermally stable up to 380 °C, along with being soluble in and processable from common organic solvents. The polymers absorb light broadly throughout the visible spectrum, with optical bandgaps of 1.70 and 1.77 eV, respectively. Both polymers reduce reversibly with LUMO energy levels at -3.84 and -3.90 eV for the homopolymer and the copolymer, respectively, close to the value of -4.10 eV found for fullerenes such as PC60BM when measured under identical conditions. The polymers HOMO levels were calculated at -5.54 and -5.67 eV, respectively, based on their optical band gaps. Spectroelectrochemical measurements on thin films of the homopolymer showed the generation of stable negative charge carriers, accompanied by colored-to-transmissive electrochromism in the films upon reduction. The n-type character of these polymers motivated the fabrication of all-polymer solar cells using blends of poly(3- hexylthiophene) and the homopolymer of isoindigo, yielding efficiencies approaching 0.5%, with room for optimization based on the observed surface morphology of the blend films. © 2011 American Chemical Society. Source


Stalder R.,George and Josephine Butler Polymer Research Laboratory | Xie D.,George and Josephine Butler Polymer Research Laboratory | Zhou R.,University of Florida | Xue J.,University of Florida | And 3 more authors.
Chemistry of Materials | Year: 2012

Three linear asymmetrically functionalized conjugated molecules composed of five or six aromatic rings were synthesized, bearing a terminal phosphonic acid group, with the objective of enabling their grafting onto inorganic CdSe nanocrystals. These chromophores - oligo(phenylene ethynylenes), oligothiophenes, or donor-acceptor-donor oligothiophenes with a benzothiadiazole acceptor - were designed with decreasing HOMO-LUMO energy gaps such that increasing amounts of light could be absorbed toward the longer wavelengths up to 600 nm. Electrochemical measurements show that the energy offsets between the HOMO and LUMO energies of the organic molecules and the energy bands of the CdSe nanocrystals are well-suited for charge transfer between the organic and inorganic components. The characteristics of each component's excited state are studied by fluorescence spectroscopy and the interaction between the conjugated molecules and the CdSe nanocrystals in dilute solutions is monitored by photoluminescence quenching. In the latter experiments, where ester and acid derivatives are compared, the pronounced difference in luminescence quenching supports the ability of the phosphonic acid groups to strongly anchor onto the surface of the nanocrystals. Moreover, these results suggest that charge transfer likely occurs between the organic and the inorganic compounds, and appropriate ratios for the corresponding organic/inorganic hybrids preparation are identified. The preparation by direct ligand exchange and the photophysical properties of the hybrids are described, and spectroscopic analysis estimates that the nanocrystals are covered, on average, with 100-200 electroactive organic molecules. The incident photon-to-electron conversion efficiency reflects the solution absorption of the hybrids because it shows the response from both organic and inorganic components. © 2012 American Chemical Society. Source


Ertas M.,George and Josephine Butler Polymer Research Laboratory | Walczak R.M.,George and Josephine Butler Polymer Research Laboratory | Das R.K.,University of Florida | Rinzler A.G.,University of Florida | And 2 more authors.
Chemistry of Materials | Year: 2012

This paper reports a novel supercapacitor electrode design based on poly(3,4-propylenedioxypyrrole) (PProDOP) electropolymerized onto thin films of single walled carbon nanotubes (SWNTs) on glass substrates. This permits the electropolymerization of thicker PProDOP films than can be deposited onto flat gold-coated Kapton electrodes and a correspondingly greater capacitance per unit area. A pyrene functionalized polyfluorene, designated Sticky-PF, was designed and used as an effective monolayer interfacial adhesion modifier between the SWNT films and PProDOP via noncovalent self-assembly onto the SWNT film surfaces before polymer electrodeposition. The thickness of the electrodeposited PProDOP was found to be self-limiting at thicknesses characteristic of each substrate electrode. Optimized areal capacitance values for PProDOP on flat gold and Sticky-PF coated SWNT films were measured to be 8.1 mF/cm 2 and 16.4 mF/cm 2, respectively, with the twofold enhancement due to the thicker films possible on the SWNT electrode. The specific capacitance of PProDOP on gold and Sticky-PF|SWNT film substrates were found to be similar at 141 F/g and 122 F/g, respectively, indicating the capacitance to be due to the electroactive polymer. The areal capacitance values of the corresponding supercapacitor devices constructed with Au/Kapton substrates was 3.2 mF/cm 2, whereas a significantly greater value of 8.8 mF/cm 2 was measured for the Sticky-PF|SWNT film substrates. The supercapacitors prepared using the Au/Kapton substrates were highly stable, retaining 80% of their electroactivity after 32 700 nonstop charge/discharge cycles (100% depth of discharge). Supercapacitors made using the Sticky-PF|SWNT substrates showed a steady loss of capacitance to about 57% of the original value (to 5.0 mF/cm 2) after 32 700 charge/discharge cycles, which was still 38% larger than the initial capacitance of the gold electrode devices. © 2012 American Chemical Society. Source

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