Benzodifuran‐containing well‐defined π‐conjugated polymers for photovoltaic cells

Two well‐defined alternating π‐conjugated polymers containing a soluble electroactive benzo[1,2‐b:4,5‐b′]difuran (BDF) chromophore, poly(BDF‐(9‐phenylcarbazole)) (PBDFC), and poly(BDF‐benzothiadiazole) (PBDFBTD) were synthesized via Sonogashira copolymerizations. Their optical, electrochemical, and field‐effect charge transport properties were characterized and compared with those of the corresponding homopolymer PBDF and random copolymers of the same overall composition. All these polymers cover broad optical absorption ranges from 250 to 750 nm with narrow optical band gaps of 1.78–2.35 eV. Both PBDF and PBDFBTD show ambipolar redox properties with HOMO levels of ?5.38 and ?5.09 eV, respectively. The field‐effect mobility of holes varies from 2.9 × 10^?8 cm² V^?1 s^?1 in PBDF to 1.0 × 10^?5 cm² V^?1 s^?1 in PBDFBTD. Bulk heterojunction solar cell devices were fabricated using the polymers as the electron donor and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester as the electron acceptor, leading to power conversion efficiencies of 0.24–0.57% under air mass 1.5 illumination (100 mW cm^?2). These results indicate that their band gaps, molecular electronic energy levels, charge mobilities, and molecular weights are readily tuned by copolymerizing the BDF core with different π‐conjugated units. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Finite size effect on the Raman frequency of phonons in nano-semiconductors

A comprehensive study on Raman spectroscopy with different excitation wavelengths, sample sizes, and sample shapes for optic phonons (OPs) and acoustic phonons (APs) in polar and non-polar nano-semiconductors has been performed. The study affirms that the finite size effect does not appear in the OPs of polar nano-semiconductors, while it exists in all other types of phonons. The absence of the FSE is confirmed to originate from the long-range Fr¨ohlich interaction and the breaking of translation symmetry. The result indicates that the Raman spectra of OPs cannot be used as a method to characterize the scale and crystalline property of polar nano-semiconductors.     

Synthesis and thermal energy storage properties of the polyurethane solid–solid phase change materials with a novel tetrahydroxy compound

Based on the phase change theory, a novel tetrahydroxy compound (THCD) was designed and prepared. Depending on the spatial structure of the tetrahydroxy compound, a form-stable thermoplastic polyurethane solid–solid phase change material (TPUPCM) was synthesized via employing PEG as soft segments, while multi-benzene ring structure made by 4,4′-diphenylmethane diisocyanate and tetrahydroxy compound as hard segments. The composition and structure of THCD and TPUPCM, the TPUPCM’s the weight average molecular weight and number average molecular weight, dissolving and melting abilities, phase change behaviors, thermal performances and crystalline morphology were investigated by Fourier transform infrared spectrometer, ¹H nuclear magnetic resonance spectrometer, multiangle laser light scattering apparatus, differential scanning calorimentry, dynamic mechanical thermal analysis, thermogravimetry analysis system, wide-angle X-ray diffraction, polarizing optical microscopy. The results show that the solid–solid phase change material owns excellent phase change properties and a broad processing temperature range. The heating cycle phase change enthalpy is 137.4 J/g, and the cooling cycle phase change enthalpy is 127.6 J/g. The started decomposition temperature and the maximum decomposition temperature are at 323.5 and 396.2 °C, respectively. Furthermore, the solid–solid phase change material is dissolvable, meltable and can be processed directly, and has great potential applications in thermal energy storage.     

From Nitro‐ to Sulfonyl‐Based Chromophores: Improvement of the Comprehensive Performance of Nonlinear Optical Dendrimers

Through the combination of the divergent and convergent approaches, coupled with the utilization of the powerful Sharpless “click‐chemistry” reaction, two series of sulfonyl‐based high‐generation NLO dendrimers were conveniently prepared with high purity and in satisfactory yields. Thanks to the perfect three‐dimensional (3D) spatial isolation from the highly branched structure and the isolation effect of the exterior benzene moieties and the interior triazole rings, these dendrimers exhibited large second harmonic generation coefficient (d₃₃) values up to 181 pm V^?1, which, to the best of our knowledge, is the highest value so far for polymers containing sulfonyl‐based chromophore moieties. Meanwhile, compared with the nitro‐chromophore‐based analogues, their optical transparency and NLO stability were improved in a large degree, due to the lower dipole moment (μ) and the special main‐chain structure of sulfonyl‐based chromophore in these dendrimers.     

New Synthetic Method of p-Nitrocalixarenes

Calixarenes 1 were directly nitrated with potassium nitrate and aluminum chloride to give p-nitrocalixarenes 2 in good yields. Formation of p-nitrocalix[4]arene (2a) from reaction of p-bromomethylcalix[4]arene (3) with silver nitrate is also described.     

二维半导体材料与器件——从传统二维光电材料到石墨炔

近年来,二维半导体材料由于其独特的材料结构和电子输运特性得到了科学界的广泛关注,被应用于光电器件、催化和生物传感器等领域。本文系统概述了传统二维材料以及新兴二维材料石墨炔的发现和发展历程。重点聚焦在二维材料在光探测器领域中的应用,探讨了不同二维材料体系及器件结构对光探测器性能的影响;并详细介绍了新兴二维材料——石墨炔,及其合成和应用。展望了传统二维材料及石墨炔在光电转换器件的应用中所面临的机遇和挑战。