Chiral Conjugated Molecular Assemblies Interact with Substances and Light

ConspectusChirality has been relevant to numerous core scientific topics over the past century. Recently, the value of chirality in artificial functional materials has been recognized and investigated intensively. Functional materials with chirality demonstrate some characteristic properties lacking in their achiral counterparts. Specifically, in chiral materials, optical rotatory dispersion, circular dichroism (CD), circularly polarized luminescence, nonlinear optical effect, and chiral-induced spin selectivity have been observed. These unique properties have recently stimulated increasing research interest in circularly polarized light (CPL) detection, circularly polarized photoluminescence and electroluminescence, chiral spintronic devices, etc. Generally speaking, the interdisciplinary chirality and optoelectronics will not only promise new opportunities for fundamental scientific research but also show broad application prospects in 3D display, drug screening, quantum computing and communication, information encryption transmission and processing, etc.In this context, chiral organic optoelectronic materials provide an appealing platform for investigation. In addition to the outstanding optical and electronic properties, chirality can be easily introduced into organic optoelectronic materials via either valence or nonvalence chemistry and can be transferred from the molecular level to the supramolecular, nano/micro, and even macro levels by molecular self-assembly and supramolecular chemistry. Moreover, chiral organic molecules are compatible with most cutting-edge processing techniques, such as vacuum evaporation, spin-coating, blade coating, roll-to-roll, etc., for various types of devices. These optoelectronic devices, including organic solar cells (OSCs), organic field-effect transistors (OFETs), and organic light-emitting diodes (OLEDs), can be manufactured on either rigid or flexible substrate, covering device size from molecular scale (single molecule device) to nano/micro and large area in square meter scale. It is thus worthwhile to review the role of chirality in organic optoelectronic materials and devices to promote further development of chiral organic optoelectronics.In this Account, we intend to showcase the diverse functions empowered by the intriguing properties of chiral organic conjugated molecular assemblies. We will first discuss how chirality affects molecular packing in chiral organic assemblies, from which we will show chirality not only helps elucidate the intermolecular interactions but also impacts hierarchical structures in matters. We then expand the discussion to the interactions between chiral assemblies and guest substances, complicated helical motion, and molecular chirality recognition achieved at nano, micro, or even macro level. We highlight our recent advances in the interactions between chiral assemblies and chiral light. This generates the field of direct CPL detection, and the basic principles in this field will be summed up. Specifically, the underlying mechanism of selective CPL detection by chiral photodiodes and phototransistors, with the principles of down-to-earth optoelectronics, will be addressed. Overall, we outline chiral optoelectronic functional assemblies and devices that provide a promising approach to perceiving chiral entities that are unable to be distinguished by the human senses directly. Finally, we conclude the difficulties and challenges for chiral π-conjugated materials and devices at the present stage and propose perspectives that could be further conducted to boost the chiral optoelectronic materials and devices toward potential applications

Gamma-Irradiated Carbon Nanotube Yarn As Substrate for High-Performance Fiber Supercapacitors

As an electrical double layer capacitor, dry-spun carbon nanotube yarn possesses relatively low specific capacitance. This can be significantly increased as a result of the pseudocapacitance of functional groups on the carbon nanotubes developed by oxidation using a gamma irradiation treatment in the presence of air. When coated with high-performance polyaniline nanowires, the gamma-irradiated carbon nanotube yarn acts as a high-strength reinforcement and a high-efficiency current collector in two-ply yarn supercapacitors for transporting charges generated along the long electrodes. The resulting supercapacitors demonstrate excellent electrochemical performance, cycle stability, and resistance to folding–unfolding that are required in wearable electronic textiles

Probing the Sensory Property of Perylenediimide Derivatives in Hydrazine Gas: Core-Substituted Aromatic Group Effect

In this contribution, four perylenediimide derivatives (PTCDIs) with different core-substituted aromatic groups were prepared. Studies on their sensing properties in hydrazine vapor (10 ppm)  suggested ∼5 orders of the magnitude in increased current for core-phenyl-substituted DEY was achieved and this value is 9, 9, and 24 times higher than that of core-pyridyl-substituted DSPY, DFPY, and DTPY, respectively. The differential response to the hydrazine vapor is less dependent on their surface area and morphologies. The lower LUMO energy and activation energy with smaller interplanar spacing allows DEY highly efficient sensing performance. A similar face–face packing mode and LUMO energy of DSPY and DFPY lead to both of them exhibiting the same sensing performance, while higher LUMO energy and head-to-tail packing modes with a greater interplanar spacing induce the less-efficient sensing performance of DTPY sensors. Discussions for structure–function relationships suggested that aromatic groups in the bay region have significant impact on PTCDI sensing performance by modulating energy level, interplanar spacing, and stacking modes

Core-Spun Carbon Nanotube Yarn Supercapacitors for Wearable Electronic Textiles

Linear (fiber or yarn) supercapacitors have demonstrated remarkable cyclic electrochemical performance as power source for wearable electronic textiles. The challenges are, first, to scale up the linear supercapacitors to a length that is suitable for textile manufacturing while their electrochemical performance is maintained or preferably further improved and, second, to develop practical, continuous production technology for these linear supercapacitors. Here, we present a core/sheath structured carbon nanotube yarn architecture and a method for one-step continuous spinning of the core/sheath yarn that can be made into long linear supercapacitors. In the core/sheath structured yarn, the carbon nanotubes form a thin surface layer around a highly conductive metal filament core, which serves as current collector so that charges produced on the active materials along the length of the supercapacitor are transported efficiently, resulting in significant improvement in electrochemical performance and scale up of the supercapacitor length. The long, strong, and flexible threadlike supercapacitor is suitable for production of large-size fabrics for wearable electronic applications

Incorporation of Azo-Linkage to Elevate the Redox Potential of Triphenylamine-Based Porous Organic Polymer Cathodes for Li-Ion Batteries

Porous organic polymers with triphenylamine (TPA) subunits have attracted a lot of attention as advanced electrodes for Li-ion batteries (LIBs) but with poor rate performance and low stability. In this work, azo-linkage has been incorporated into TPA-based porous organic polymers to increase the redox potential while maintaining the capacity of TPA. The cathodes based on azo-linked porous organic polymers (Azo-POP-10, Azo-POP-11, and Azo-POP-12) exhibited a high redox potential of 3.8 V and can be charged up to 4.5 V. A stable electrochemical performance is observed and our designed cathodes retain 84% (Azo-POP-10), 87% (Azo-POP-11), and 75% (Azo-POP-12) of their initial capacities at a current density of 1000 mAg–1. Over 60% capacity retention is observed even after 1000 charge–discharge cycles. Moreover, the cathodes still delivered a stable capacity even at a very high current density of 20,000 mAg–1, showing excellent stability under fast charging conditions. A cutoff potential of 4.5 V and a current density of 20,000 mAg–1 are the highest parameters for TPA-based materials to date. The unique material design is mainly responsible for this excellent performance, and we believe that this report can inspire the further development of organic cathodes with fast charging and better stability

P3HT-Based Photovoltaic Cells with a High <i>V</i>_oc of 1.22 V by Using a Benzotriazole-Containing Nonfullerene Acceptor End-Capped with Thiazolidine-2,4-dione

A novel A₂–A₁–D–A₁–A₂-type nonfullerene acceptor, using thiazolidine-2,4-dione (TD) as the terminal acceptor (A₂) for the first time, was designed and synthesized. The final molecule, BTA2, shows a high-lying lowest unoccupied molecular orbital (LUMO) of −3.38 eV and a wide optical band gap of 2.00 eV. Fullerene-free organic solar cells based on P3HT:BTA2 realized a high open-circuit voltage (<i>V</i>_oc) of 1.22 V with a power conversion efficiency (PCE) of 4.50%. These values are significantly higher than those of the PC₆₁BM-based control device (<i>V</i>_oc = 0.61 V, PCE = 3.67%), which indicates the feasibility of thiazolidine-2,4-dione to construct nonfullerene small-molecule acceptors with high <i>V</i>_oc and PCE

Rational Design of Ternary-Phase Polymer Solar Cells by Controlling Polymer Phase Separation

In this article, we report a novel route to control the ternary-phase morphology of the active layer of polymer solar cells (PSCs). Two typical polymers with complementary absorption ranges, i.e. poly­(3-hexylthiophene) (P3HT) and poly­[(4,4′-bis­(2-ethylhexyl)­dithienol­[3,2-<i>b</i>:2′,3′-<i>d</i>]­silole)-2,6-diyl-<i>alt</i>-(2,1,3-benzothiadiazole)-4,7-diyl] (PSBTBT), are selected to obtain ternary phase system by blending with (6,6)-phenyl-C71 butyric acid methyl ester (PC₇₁BM). A more than three times increase of power conversion efficiency is observed by tuning the morphologies of ternary phase with high second polymer loading. Different from the traditional disordered intermixing morphologies, the existence of submicrometer scale domains of polymer-rich phases are observed for P3HT and PSBTBT, respectively. The measurements of photoluminescence quenching demonstrate that with the morphology varying from intermixed to hierarchical morphology, the interactions between two polymers changing from charge transfer (CT) to fluorescence resonant energy transfer (FRET); at the same time charge transfer mainly occurs at polymers and PC₇₁BM interfaces. The photophysical process here is different from previous reports. A model named hierarchical interpenetrating networks model (HINM) is proposed to describe the optimal active layer of ternary-phase PSCs. Further Kelvin probe force microscopy (KPFM) results demonstrate the reason for our relatively low efficiency is limited by PSBTBT charge transport in blend matrix. We believe that this novel route for controlling morphology could be further optimized and would provide new thoughts and opportunities in the area of PSCs

Conjugated Polymer–Small Molecule Alloy Leads to High Efficient Ternary Organic Solar Cells

Ternary organic solar cells are promising candidates for bulk heterojunction solar cells; however, improving the power conversion efficiency (PCE) is quite challenging because the ternary system is complicated on phase separation behavior. In this study, a ternary organic solar cell (OSC) with two donors, including one polymer (PTB7-Th), one small molecule (<i>p</i>-DTS­(FBTTH₂)₂), and one acceptor (PC₇₁BM), is fabricated. We propose the two donors in the ternary blend forms an alloy. A notable averaged PCE of 10.5% for ternary OSC is obtained due to the improvement of the fill factor (FF) and the short-circuit current density (<i>J</i>_sc), and the open-circuit voltage (<i>V</i>_oc) does not pin to the smaller <i>V</i>_oc of the corresponding binary blends. A highly ordered face-on orientation of polymer molecules is obtained due to the formation of an alloy structure, which facilitates the enhancement of charge separation and transport and the reduction of charge recombination. This work indicates that a high crystallinity and the face-on orientation of polymers could be obtained by forming alloy with two miscible donors, thus paving a way to largely enhance the PCE of OSCs by using the ternary blend strategy

Self-Assembly of Well-Defined Poly(3-hexylthiophene) Nanostructures toward the Structure–Property Relationship Determination of Polymer Solar Cells

The control of the nanoscale morphology of the active layer is vital to obtaining high-performance polymer solar cells (PSCs). In this study, the effects of the nanowire length on the nanoscale organization of the active layer as well on the final performance of PSCs based on poly­(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are presented. P3HT nanowires with different lengths were obtained by sonication-assisted self-assembly. The nanowire length increased as the temperature increased during sonication. PSCs based on P3HT nanowires/PCBM blends with different nanowire lengths were fabricated, and their performance was systemically investigated. When the P3HT nanowire length increased, the short-circuit current (<i>J</i>_sc) and fill factor (FF) of the devices were both enhanced, which resulted in a higher performance. Morphological characterization of the active layer showed that the longer P3HT nanowires in the active layer have a higher tendency to form interpenetrating network structures that facilitate the charge transport in the active layer

Controllable Supramolecular Chiral Twisted Nanoribbons from Achiral Conjugated Oligoaniline Derivatives

The fabrication of supramolecular chiral nanostructures from achiral materials without the need of pre-existing chirality is a major challenge associated with the origin of life. Herein, supramolecular chiral twisted nanoribbons of achiral oligoaniline derivatives were prepared via simply performing the chemical oxidation of aniline in an alcohol/water mixed solvent. In particular, the supramolecular chirality of the twisted nanoribbons could be controlled by facilely tuning the alcohol content in the mixed solvent. A tetra-aniline derivative C₂₄H₂₀O₃N₄ was attested to be the major component of the obtained nanoribbons. The main driving forces for the assembly of the oligoaniline derivative into twisted nanoribbons might be the π–π stacking and hydrogen bonding interactions among the chains which could be modulated by the alcohol content in the mixed solvent. The single-handed twisted nanoribbons could be used to separate chiral phenylalanine from a racemic mixture. Thus, it is highly anticipated that the supramolecular chirality endows π-conjugated molecules with potential application in chiral recognition