Conjugated backbones play a fundamental role in determining the electronic properties of organic semiconductors. On the basis of two solution-processable dihydropyrrolo[3,4-c]pyrrole-1,4-diylidenebis(thieno[3,2-b]thiophene) derivatives with aromatic and quinoid structures, we have carried out a systematic study of the relationship between the conjugated-backbone structure and the thermoelectric properties. In particular, a combination of UV–vis–NIR spectra, photoemission spectroscopy, and doping optimization are utilized to probe the interplay between energy levels, chemical doping, and thermoelectric performance. We found that a moderate change in the conjugated backbone leads to varied doping mechanisms and contributes to dramatic changes in the thermoelectric performance. Notably, the chemically doped A-DCV-DPPTT, a small molecule with aromatic structure, exhibits an electrical conductivity of 5.3 S cm–1 and a high power factor (PF373 K) up to 236 μW m–1 K–2, which is 50 times higher than that of Q-DCM-DPPTT with a quinoid structure. More importantly, the low thermal conductivity enables A-DCV-DPPTT to possess a figure of merit (ZT) of 0.23 ± 0.03, which is the highest value reported to date for thermoelectric materials based on organic small molecules. These results demonstrate that the modulation of the conjugated backbone represents a powerful strategy for tuning the electronic structure and mobility of organic semiconductors toward a maximum thermoelectric performance.

A graphene-like coordination polymer based on copper(II) benzenehexathiol (Cu-BHT, 1) with high electric conductivity (103 S·cm–1) was prepared recently. The high conductivity makes this material a good candidate for electrocatalysis, and here its catalytic activity toward hydrogen evolution reaction (HER) was evaluated. Cu-BHT shows good activity and stability for HER in acidic solutions under high current densities. By changing the preparation conditions, the morphology of Cu-BHT materials was controlled at the mesoscale, which allows the preparation of a thin film (TF-1), nanocrystal (NC-1), and amorphous nanoparticle (NP-1) of Cu-BHT. The overpotential of Cu-BHT toward HER shows an improved activity from 760 mV (NC-1) to 450 mV (NP-1) at a current density of 10 mA·cm–2. A Tafel slope of ∼95 mV·dec–1 and an exchange current density of 10–3 mA·cm–2 were achieved under optimized conditions. Density functional theory calculations suggest that the “Cu-edge site” on the (100) surface plays an important role in improving the HER catalytic performance of Cu-BHT nanoparticles.Keywords: coordination polymers; hydrogen evolution reaction; metal−dithiolene; morphology control; nanoparticles;

•Synthesis and characterization of two new type trisphenols.•Superior thermal stability and highly antioxidant efficiency.•The relationship between structure and properties explored by DFT calculations.Two kinds of trisphenols have been successfully synthesized and their structures were confirmed by IR spectra, 1HNMR, 13CNMR, mass spectra and X-ray diffraction. They exhibited better thermal stability than both monophenol and bisphenols due to their higher molecular weight. Moreover, their antioxidant activities have been investigated in lubricant oil using PDSC and RBOT. The results showed that the o-trisphenol 3b exhibited the best antioxidant activity while the p-trisphenol 3a was the worst. In addition, their relationship between structures and properties has been further explored by a series of DFT calculations including the BDE values, the IP values and the Gibbs free energy barriers for the reaction between phenols and methylperoxyl radicals.Download high-res image (55KB)Download full-size image

Here, we present our recent progress on the synthesis, crystal structure, physical properties and DFT calculations of a novel large pyrene-fused N-heteroacene (15RINGS) with 15 aromatic six-membered rings linearly fused in one row. The long conjugated backbone (more than 35 Å) of 15RINGS possesses a dual-bending feature (the bending angle is about 13.2°).

Sulfur-doped graphene quantum dots (S-GQDs) with stable blue-green fluorescence were synthesized by one-step electrolysis of graphite in sodium p-toluenesulfonate aqueous solution. Compared with GQDs, the S-GQDs drastically improved the electronic properties and surface chemical reactivities, which exhibited a sensitive response to Fe3+. Therefore, the S-GQDs were used as an efficient fluorescent probe for highly selective detection of Fe3+. Upon increasing of Fe3+ concentration ranging from 0.01 to 0.70 μM, the fluorescence intensity of S-GQDs gradually decreased and reached a plateau at 0.90 μM. The difference in the fluorescence intensity of S-GQDs before and after adding Fe3+ was proportional to the concentration of Fe3+, and the calibration curve displayed linear regions over the range of 0–0.70 μM. The detection limit was 4.2 nM. Finally, this novel fluorescent probe was successfully applied to the direct analysis of Fe3+ in human serum, which presents potential applications in clinical diagnosis and may open a new way to the design of effective fluorescence probes for other biologically related targets.

A novel donor–acceptor (D–A) copolymer PDFCDTBT with 3,6-difluoro substituted carbazole as the donor unit and dialkoxy substituted benzothiadiazole as the acceptor unit has been synthesized and used as a donor material for bulk heterojunction polymer solar cells (BHJ PSCs). PDFCDTBT possesses a band gap of 1.75 eV, a low-lying HOMO energy level of −5.23 eV, and a good thermal and electrochemical stability. In comparison with the corresponding non-fluoro substituted HXS-1, which has a HOMO energy level of 5.21 eV, a LUMO energy level of 3.35 eV, and an optical band gap of 1.86 eV, the incorporation of two fluoro atoms in the carbazole donor unit lowers the HOMO and the LUMO energy levels of the polymer, which results in simultaneously decreasing the band gap of the polymer and increasing the Voc of polymer solar cells. The fluoro-containing polymer PDFCDTBT also shows strong intramolecular interactions and forms close packing in the solid state. Polymer solar cells based on PDFCDTBT and (6,6)-phenyl-C71-butyric acid methyl ester (PC71BM) demonstrate a power conversion efficiency (PCE) of 4.8% with a Voc of 0.91 V, a Jsc of 9.5 mA cm−2, and an FF of 0.55. In comparison with HXS-1, the better stability, higher Voc, and narrower band gap indicate that PDFCDTBT is a very promising donor material for high efficiency polymer solar cells.

Here, we present our recent progress on the synthesis, crystal structure, physical properties and DFT calculations of a novel large pyrene-fused N-heteroacene (15RINGS) with 15 aromatic six-membered rings linearly fused in one row. The long conjugated backbone (more than 35 Å) of 15RINGS possesses a dual-bending feature (the bending angle is about 13.2°).