Weigang Zhu

Revealing the Charge-Transfer Interactions in Self-Assembled Organic Cocrystals: Two-Dimensional Photonic Applications

A new crystal of a charge-transfer (CT) complex was prepared through supramolecular assembly and it has unique two-dimensional (2D) morphology. The CT nature of the ground and excited states of this new Bpe-TCNB cocrystal (BTC) were confirmed by electron spin resonance measurements, spectroscopic studies, and theoretical calculations, thus providing a comprehensive understanding of the CT interactions in organic donor-acceptor systems. And the lowest CT1 excitons are responsible for the efficient photoluminescence (Φ(PL)=19%), which can actively propagate in individual 2D BTCs without anisotropy, thus implying that the optical waveguide property of the crystal is not related to the molecular stacking structure. This unique 2D CT cocrystal exhibits potential for use in functional photonic devices in the next-generation optoelectronic communications.

Precisely Tailoring the Stoichiometric Stacking of Perylene‐TCNQ Co‐Crystals towards Different Nano and Microstructures with Varied Optoelectronic Performances

Organic charge-transfer co-crystals with varied donor-acceptor stoichiometric ratios and molecular packing structures are controllably prepared with the morphology of nanowires or microblocks. They have distinct charge transport behavior and photoresponsivity. These interesting results pave the way for rational design and preparation of co-crystals with desired functions.

Quick Fabrication of Large-area Organic Semiconductor Single Crystal Arrays with a Rapid Annealing Self-Solution-Shearing Method

In this paper, we developed a new method to produce large-area single crystal arrays by using the organic semiconductor 9, 10-bis (phenylethynyl) anthracene (BPEA). This method involves an easy operation, is efficient, meets the demands of being low-cost and is independent of the substrate for large-area arrays fabrication. Based on these single crystal arrays, the organic field effect transistors exhibit the superior performance with the average mobility extracting from the saturation region of 0.2 cm2 V−1s−1 (the highest 0.47 cm2 V−1s−1) and on/off ratio exceeding 105. In addition, our single crystal arrays also show a very high photoswitch performance with an on/off current ratio up to 4.1 × 105, which is one of the highest values reported for organic materials. It is believed that this method provides a new way to fabricate single crystal arrays and has the potential for application to large area organic electronics.

Deepening Insights of Charge Transfer and Photophysics in a Novel Donor-Acceptor Cocrystal for Waveguide Couplers and Photonic Logic Computation.

The charge transfer and photophysics in a new light-emitting cocrystal with ribbon-like morphology are revealed in-depth. These cocrystals can serve as an efficient 1D optical waveguide, and the cocrystal waveguide couplers fabricated by a probe-assisted crystal-moving technique exhibit interfacial white emission and can function as basic photonic logic gates, showing potential for future integrated photonics.

A cross-dipole stacking molecule of an anthracene derivative: integrating optical and electrical properties

Cross-dipole stacking has been addressed as a preferred motif for solid state emission, but inefficient for charge transport. Here we synthesize a new anthracene derivative, which adopts cross-stacking in the solid state with a solid state fluorescence up to 77.3% and a hole mobility of 1.47 cm2 V−1 s−1, integrating optical and electrical properties successfully. As far as we know, it is the first report of organic field-effect transistors based on cross-dipole stacking molecules.

Recent advances in one-dimensional organic p–n heterojunctions for optoelectronic device applications

With the rapid development of organic electronics, one-dimensional (1D) organic p–n heterojunctions have attracted increasing interest because of their unique optoelectronic properties and potential as building blocks for sophisticated integrated circuits. Recently, significant progress has been made in the methods for synthesizing or fabricating 1D organic p–n heterojunctions, including two typical types of organic–organic heterojunctions and organic–inorganic heterojunctions. Various device applications have been demonstrated based on these 1D organic heterojunctions with new or enhanced optical and/or electrical properties. This MiniRev highlights the recent remarkable advances in this field with a concise summary of the various preparation methods such as solution process, physical vapor techniques, template and templateless methods, etc., to form segmented, cross-stacked, bilayer, and core–shelled structures. The potential applications of these 1D organic heterojunctions in optoelectronic devices, such as ambipolar transistors, photovoltaics, photodetectors and diodes, are demonstrated in the second part. Finally, the challenges and potential opportunities existing in this field are also deeply discussed.

Challenges of organic “cocrystals”

Organic cocrystal (also “co-crystal”), formed with two or more different components via non-covalent intermolecular interactions, possesses novel, unpredicted and unique properties, which are not the simple sum of those molecular components, e.g., with effect of 1+1>2. In this regard, organic cocrystals provide a distinctive strategy for the synthesis of novel multifunctional materials, and an important platform for exploring new fundamental physicochemical phenomena in molecular systems, such as high conductivity, ambipolar charge transportation, photovoltaic behavior, white light-emitting, room-temperature phosphorescence, nonlinear optics and ferroelectricity etc., with potential application even in liquid crystal engineering and drug industry.中文摘要本文简明扼要地介绍了“有机共晶”这个重要研究领域的兴起和发展过程, 在有争议的方面, 如共晶定义和如何判定分子排布等, 给出了作者独到的见解. 特别重要的是, 通过阐述该领域当前存在的问题和挑战, 结合分析最新的研究进展和结果, 使得人们对共晶的认识更为系统和深入. 基于此, 作者同时分析和指出了未来可能重点发展的研究方向.

Pyridyl-substituted anthracene derivatives with solid-state emission and charge transport properties

We report here a systematic study of the solid-state packing, optoelectronic properties and organic field-effect transistor properties of three isomeric 2,6-di-pyridyl anthracene derivatives (1a, 1b and 1c). Very different solid-state physicochemical behaviours were found as a result of the subtle change in the substitution site, especially in the solid-state emission and charge transport properties. For 1a and 1b, which adopted H-like aggregates in the solid state, a bright blue emission with fluorescent quantum efficiencies (ΦF) of 50.2 and 17.5% and thin film mobilities of 0.05 and 10−5 cm2 V−1 s−1, respectively, were obtained. The inferior mobility of 1b might be caused by the larger torsion and herringbone angle in the solid-state packing. A green emission with ΦF of 16% was obtained for single crystals of 1c. No charge transport property was observed for 1c, which might be related to the unfavourable solid-state packing and poor film morphology.

Perylene crystals: tuning optoelectronic properties by dimensional-controlled synthesis

One-dimensional (1D) ribbon-like and two-dimensional (2D) square-like perylene crystals were prepared in a controlled manner via a simple drop-casting solution method by changing the temperature and concentration of the solution. Based on SAED and XRD results, both the ribbon and square perylene crystals belong to the α phase. From further optical and electronic characterizations, we find that perylene crystals show unique dimension-dependent optoelectronic properties. In 2D crystal, photons propagate along the two edge directions without anisotropy, indicating that the optical waveguide property may not be related to molecular packing. Propagation of photons along the direction of the axis in the 1D crystal seems to be a little more efficient than that in the 2D structure. Moreover, hole mobility of the 1D crystal is the same as that along the [001] direction of the 2D square sheet, while hole carriers are transported along the two directions of square sheet with an anisotropy about 2.3. This excellent example shows that the optical waveguide and field-effect mobility of an organic crystal can be tuned by controlling the number of dimensions of the crystal during the synthesis.

Organic Cocrystals: New Strategy for Molecular Collaborative Innovation.

Organic cocrystals that are composed of two or more components usually exhibit novel, unpredictable, and even unique properties rather than a simple combination of the properties of their components, such as white-light emission, ambipolar charge transport, nonlinear optics, and ferroelectricity. Since cocrystal engineering represents a novel strategy for synthesizing multifunctional materials, which opens the door for molecular collaborative innovation, it has aroused much attention in recent years. However, as it is also a relatively new research field, it is only in its early stages of development. In order to provide readers with an understanding of the future design of cocrystals for potential applications, a brief review of organic cocrystals is presented here, including an introduction to organic cocrystals as well as discussions of cocrystal preparation, methods and techniques of characterization, and multifunctional applications of cocrystals. Moreover, the outlook for further studies and applications of cocrystal engineering is considered.