The past five years have witnessed significant achievements in the field of flexible, stretchable, and printable organic electronics, especially polymer-based organic photovoltaics (OPVs) and organic fieldeffect transistors (OFETs), which have become competitive to their inorganic counterparts. One of the main driving forces attributed to this remarkable progress is the rapid development of semiconducting 10 polymeric materials. Therefore, the design and synthesis of new building blocks for efficient polymer semiconductors has attracted increasing attention from both the academic and industrial communities. This review attempts to critically summarize the recent advances with respect to the electron-deficient building blocks based on benzothiadiazole and its π-extended, heteroannulated derivatives, which have been mostly developed over the past five years for constructing π-conjugated polymers, particularly 15 donor-acceptor (D-A) polymers. Semiconducting polymers containing these building blocks have demonstrated interesting properties and promising performances as active layers in OPVs and OFETs. The structural implications related to the performances of organic electronic devices are discussed. R SN SeN SeS TQ fDTBT CBT APhTQ BDTTQ BTI DTPBT DTNT TNTPT triple fused ring structures tetracyclic structures other large extended benzothiadiazole derivatives heteroatom substituted benzothiadiazolederivatives Chart 1 The chemical structures of benzothiadiazole and its π-extended, heteroannulated derivatives.Journal Name, [year], [vol], 00-00 | 13 eV. On the other hand, deep E LUMO levels can be obtained in BBT-based polymers, as represented by the E LUMO of −4.20 eV for PBBTPD (Chart 3). The difference between the E HOMO and E LUMO levels, called an electrochemical band gap, has a correlation with the end absorption of the UV-vis-NIR spectrum. 5 Notes and references 30The electron-deficient building blocks based on benzothiadiazole and its π-extended, heteroannulated derivatives for constructing high-performance semiconducting polymers are described.

New π-conjugated polymers with strong electron affinity, PNDTI-BBTs, consisting of naphtho­[2,3-b:6,7-b′]­dithiophenediimide (NDTI) and benzo­[1,2-c:4,5-c′]­bis­[1,2,5]­thiadiazole (BBT) units, were synthesized. PNDTI-BBTs have low-lying LUMO energy levels (∼−4.4 eV), which is sufficiently low for air-stable electron transport in organic field-effect transistors and for being readily doped by a well-known n-dopant, N,N-dimethyl-2-phenyl-2,3-dihydro-1H-benzoimidazole (N-DMBI), affording doped polymer films with relatively high conductivities and Seebeck coefficients. Depending on the solubilizing alkyl groups (2-decyltetradecyl, PNDTI-BBT-DT, or 3-decylpentadecyl groups, PNDTI-BBT-DP), not only the electron mobility in the transistor devices with the pristine polymer thin films (PNDTI-BBT-DT: ∼0.096 cm2 V–1 s–1; PNDTI-BBT-DP: ∼0.31 cm2 V–1 s–1) but also the conductivity and power factor of the doped thins films (PNDTI-BBT-DT: ∼0.18 S cm–1 and ∼0.6 μW m–1 K–2; PNDTI-BBT-DP: ∼5.0 S cm–1 and ∼14 μW m–1 K–2) were drastically changed. The differences in the electric properties were primarily ascribed to the better crystalline nature of the PNDTI-BBT-DP than those of PNDTI-BBT-DT in the thin-film state. Furthermore, UV–vis and ESR spectra demonstrated that doping effectiveness was largely affected by the alkyl groups: the PNDTI-BBT-DP films with better crystalline order prevented overdoping, resulting in ca. 20 times higher conductivity and power factors. From these results, it can be concluded that tuning the intermolecular interaction and consequently obtaining the thin-film with well-ordered polymers by the alkyl side chains is a promising strategy for developing superior thermoelectric materials.

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The cloud point curves of a series of oxygen-containing polymers in CO 2 were measured to attempt to deduce the effect of oxygen functional groups within a polymer on the polymer/CO 2 phase behavior. The addition of an ether oxygen to a hydrocarbon polymer, either in the backbone or the side chain, enhances "CO 2philicity" by providing sites for specific interactions with CO 2 as well as by enhancing the entropy of mixing by creating more flexible chains with higher free volume. Ab initio calculations show that both ether and ester oxygens provide very attractive interaction sites for CO 2 molecules. The binding energy for an isolated ether oxygen with CO 2 is larger in magnitude than that for a carbonyl oxygen/CO 2 complex. However, acetate functionalized polymers are more CO 2 -soluble than polymers with only ether functionalitiesspossibly because acetate functional groups contain a total of three binding modes for CO 2 interactions, compared with only one for the ether functional group. Experiments clearly indicate that adding a single methylene group as a spacer between a polymer backbone and either an ether or acetate group exhibits a strong deleterious effect on phase behavior. This effect cannot be explained from our ab initio calculations.

This work describes a nickel-catalyzed Ullmann-type thiolation of aryl iodidesunder mild electrochemical conditions. The simple undivided cell with graphene/nickel foam electrode setups offers excellent substrate tolerance, affording aryl and alkyl sulfides in good chemical yields. Furthermore, the mechanism for this electrochemical cross-coupling reaction has been investigated by cyclic voltammetry.

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Rational design and synthesis of polymeric semiconductors is critical to the development of polymer solar cells (PSCs). In this work, a new series of benzodithiophene− difuranylbenzooxadiazole-based donor−acceptor co-polymersnamely, PBDT-DFBO, PBDTT-DFBO, and PBDTF-DFBO, with various side groupshave been developed for bulk-heterojunction PSCs. These side-group substituents provide the opportunity to tailor the opto-electrical properties of the polymers. In addition, we show that the reduction of the bandgap of polymers and the enhancement of charge mobility in the devices can be accomplished concurrently by substituting the alkylthienyl side group with its furan counterpart. In the preliminary investigation, one could obtain PSCs with a power conversion efficiency (PCE) of 2.1% for PBDT-DFBO with an alkoxyl side chain, 2.2% for PBDTT-DFBO with an alkylthienyl side group, and 3.0% for PBDTF-DFBO with an alkylfuranyl side group. Further optimizing the performance of the devices was conducted via a simple solvent treatment. The PSCs based on PBDTF-DFBO:PC 71 BM could even achieve 7.0% PCE, which exhibited an enhancement of 130%. To the best of our knowledge, the value of 7.0% is the highest efficiency for furan-containing PSCs to date and is also comparable with the hitherto reported highest efficiency of the single junction PSCs. Through a combination of testing charge transport by the space-charge limited current (SCLC) model and examining the morphology by atomic force microscopy (AFM), we found that the effects of solvent treatment on the improved performance originate from higher and more balanced charge transport and the formation of fiberlike interpenetrating morphologies, which are beneficial to the increase of short-circuit current density (J sc ) and fill factor (FF). This work demonstrates a good example for tuning absorption range, energy level, charge transport, and photovoltaic properties of the polymers by side-chain engineering and the solvent treatment can offer a simple and effective method to improve the efficiency of PSCs.

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