No abstract

A planar backbone conformation is essential for enabling polymer semiconductors with high charge carrier mobility in organic thin-film transistors. Benefiting from the smaller van der Waals radius of the O atom in furan (versus the S atom in thiophene), alkylated furan exerts a reduced steric hindrance on neighboring arene, and it was found that the head-to-head (HH)-linked 3,3′-dialkyl-2,2′-bifuran (BFR) can attain a high degree of backbone planarity. Hence, BFR should be a promising building block for constructing polymer semiconductors with a planar backbone conformation and hold distinctive advantages over a dialkylbithiophene-based analogue, which is typically highly twisted. The alkyl chains on the 3 and 3′ positions offer good solubility to the resulting polymers, which in combination with its planar backbone yields an improved molecular design window for developing high-performance polymer semiconductors, particularly those with a simple molecular structure and based on the acceptor co-unit without any solubilizing chains. When incorporated into polymer semiconductors, remarkably high hole and electron mobilities of 1.50 and 0.31 cm2 V–1 s–1 are obtained for BFR-based polymers FBFR-BO and CNBFR-C18 containing fluorinated and cyano-functionalized benzothiadiazole as the acceptor co-unit, respectively. Such mobilities are the highest values for HH-linked polymers and also among the best for furan-containing polymers. The results demonstrate that HH-linked dialkylbifuran is a highly promising building block for constructing organic and polymeric semiconductors, and this new approach by incorporating HH BFR offers several distinctive advantages for developing high-performance polymer semiconductors, including effective optoelectronic property tuning using a minimal number of aromatic rings, reduced structural complexity, facile material synthesis, good material solubility, and enriching the material library. In addition, the study offers important guidelines for future development of furan-based polymers and head-to-head linkage containing organic semiconductors.

A very simple domino reaction under solvent-free conditions of various pyridine-like heterocycles with 1,2-diaza-1,3-dienes produces in good yields imidazo[1,2-a]pyridines, imidazo[1,2-a]quinolines, and imidazo[2,1-a]isoquinolines. The advantage of this one-pot transformation lies in the use of simple pyridine-like compounds without prefunctionalization of the starting heterocycles.

Biomass-derived levulinic acid (LA) is an excellent substrate to obtain high-value esters that can be used as second-generation biofuels and biofuel additives. The present study focuses on the identification and definition of the key parameters crucial for the development of chemically and environmentally efficient protocols operating in continuous-flow for the preparation of structurally diverse alkyl levulinates via the esterification of LA. We have focused on the use of solid acid catalysts consisting of sulfonated cation exchange resins and considered different aliphatic alcohols to prepare levulinates 3 and 11-17 regioselectively, and in good to high yields (50-92%). Direct correlations between several reaction parameters and catalyst activity have been investigated and discussed to set proper flow reactors that allow minimal waste production during the workup procedure, enabling Environmental factor (E-factor) values as low as ca. 0.3, full recoverability and reusability of the catalysts, and the production of levulinates up to ca. 5 gxh −1 scale.

In this paper we report the rationale and implementation of a new building block for organic electronics based on 4,8-di­(2-thienyl)-benzo­[1,2-d:4,5-d′]­bis­([1,2,3]­thiadiazole) (iso-BBT-T2) and realization of two alkyl-functionalized iso-BBT-tetrathiophene (T4) alternating copolymers (P1 with alkyl = 2DT and P2 with alkyl = 2DH). Compared to the previously investigated small molecules/polymers based on the conventional 4,8-di­(2-thienyl)-benzo­[l,2-c:4,5-c′]­bis­[ l,2,5]­thiadiazole (BBT-T2), the use of the iso-BBT heterocycle widens the polymer band gap to a region (∼1.4 eV) compatible for use in single junction solar cells. The influence of iso-BBT vs BBT structural variation on the molecular structure, electronic characteristics, and optical properties was accessed by DFT computations, single-crystal determination, optical absorption, and electrochemical measurements. In-plane charge transport for P1 and P2 was investigated in an organic thin-film transistor (OTFT) structure demonstrating hole mobilities approaching 1 cm2 V–1 s–1 and further enhanced by off-center spin-coating method to 1.32 cm2 V–1 s–1. Using PC61BM as acceptor, a remarkable PCE of 10.28% was achieved for P1 along with a current density > 20 mA/cm2. The substantial PCEs of these devices, despite the relatively narrow donor energy gap, is due to retention of high open circuit voltages ( V oc > 0.8 V) as the result of the small energy loss (E loss < 0.6 eV). Atomic force microscopy, transmission electron microscopy, and X-ray diffraction characterization further support the solar cell trends and rationalize structure–property correlations. These results demonstrate that iso-BBT-T2-based polymers are promising candidates for both organic electronics and photonic applications.