A-π-D-π-A-Based Small Molecules for OTFTs Containing Diketopyrrolopyrrole as Acceptor Units

A-π-D-π-A-based small molecules 6,6′-((thiophene-2,5-diylbis(ethyne-2,1-diyl))bis(thiophene-5,2-diyl))bis(2,5-bis(2-ethylhexyl)-3-(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione) (TDPP-T) and 6,6′-(((2,3-dihydrothieno[3,4-b][1,4]dioxine-5,7-diyl)bis(ethyne-2,1-diyl))bis(thiophene-5,2-diyl))bis(2,5-bis(2-ethylhexyl)-3-(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione) (TDPP-EDOT) have been designed and synthesized. The diketopyrrolopyrrole acts as an electron acceptor, while the thiophene or 3,4-ethylenedioxythiophene acts as an electron donor. The donor–acceptor groups are connected by an ethynyl bridge to further enhance the conjugation. The optoelectronics, electrochemical, and thermal properties have been investigated. Organic thin film transistor (OTFT) devices prepared from TDPP-T and TDPP-EDOT have shown p-type mobility. In as cast films, TDPP-T and TDPP-EDOT have shown a hole mobility of 5.44 × 10⁻⁶ cm² V⁻¹ s⁻¹ and 4.13 × 10⁻⁶ cm² V⁻¹ s⁻¹, respectively. The increase in the mobility of TDPP-T and TDPP-EDOT OTFT devices was observed after annealing at 150 °C, after which the mobilities were 3.11 × 10⁻⁴ cm² V⁻¹ s⁻¹ and 2.63 × 10⁻⁴ cm² V⁻¹ s⁻¹, respectively.

Electrochemical and Solvent-Mediated Visible-to-Near-Infrared Spectroscopic Switching of Benzoselenadiazole Fluorophores

A series of electronic push-pull, pull-pull, and push fluorophores has been prepared from a benzoselenadiazole core so that their spectroscopic, electrochemical, spectro-electrochemical, and spectro-electrofluorescence properties could be examined. The emission wavelengths and fluorescence quantum yields (Φ_fl ) of the N,N-dimethyl fluorophores were contingent on the solvent polarity and they ranged from 615 to 850 nm in aprotic solvents. The positive solvatochromism and the quenched Φ_fl in polar solvents were consistent with an intramolecular charge-transfer state (ICT). Meanwhile, a locally excited state (LE) was assigned in nonpolar solvents from the blue-shifted emission and high Φ_fl . The N,N-dimethylamine fluorophores examined could be both electrochemically oxidized and reduced, whereas the symmetric dinitro pull-pull derivative could be only reversibly reduced. Courtesy of their electrochemical reversibility, the fluorophores could reversibly change color from yellow to blue with an applied potential in addition to switching off their emission. The absorption of the electrochemically generated intermediates of the N,N-dimethyl derivatives spanned 500 nm over the visible and the NIR regions. The colors could be switched for upwards of two hours with applied potential, illustrating their potential use as electroactive materials in electrochromic devices.

Novel Two-Dimensional Conjugated Polymer Containing Fluorinated Bithiophene as Donor and Benzoselenodiazole as Acceptor Units with Vinyl-Terthiophene Pendants for Polymer Photovoltaic Cells

Novel two-dimensional conjugated copolymer, abbreviated as PDTBSeVTT-2TF, containing electron-deficient 4,7-di(thiophen-2-yl)benzo[c][1,2,5]selenodiazole (DTBSe) unit, conjugated vinyl-terthiophene (VTT) side chain and 3,3'-difluoro-2,2'-bithiophene (2TF) was designed and synthesized using microwave-assisted Stille cross-coupling polymerization. UV⁻visible absorption and cyclic voltammetry studies revealed that this copolymer possesses a strong and broad absorption in the range of 300⁻800 nm and a narrow optical bandgap (Eg) of 1.57 eV with low-lying HOMO and LUMO energy levels. Further, the bulk heterojunction polymer solar cells (PSCs) were fabricated using PDTBSeVTT-2TF as donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as acceptor with an inverted device structure of ITO/ZnO/PDTBSeVTT-2TF:PC71BM/V₂O₅/Ag. The processing temperature of blend solution for preparing PDTBSeVTT-2TF:PC71BM active layer showed obvious impact on the photovoltaic performance of solar devices. The cell fabricated from the blend solution at 65 °C exhibited enhanced power conversion efficiencies (PCE) of 5.11% with a Jsc of 10.99 mA/cm-2 compared with the one at 50 °C, which had a PCE of 4.69% with a Jsc of 10.10 mA/cm-2. This enhancement is due to the dissolution of PDTBSeVTT-2TF clusters into single molecules and small aggregates, improving the miscibility between the polymer and PC71BM and thus increasing the donor/acceptor interface.

Can time-dependent density functional theory predict intersystem crossing in organic chromophores? A case study on benzo(bis)-X-diazole based donor–acceptor–donor type molecules

Here we utilized new diagnostic tools in time-dependent density functional theory to explain the trend of intersystem crossing in benzo(bis)-X-diazole based donor–acceptor–donor type molecules.

Low-temperature sol–gel processed AlOx gate dielectric buffer layer for improved performance in pentacene-based OFETs

An approach to achieve improved performance in pentacene-based organic field effect transistors (OFETs) using high-k AlO_x prepared by a low temperature sol–gel technique as a thin buffer layer on a SiO₂ gate dielectric was demonstrated.