Xiaoyan Zheng

Charge-Transfer Complex Crystal Based on Extended-π-Conjugated Acceptor and Sulfur-Bridged Annulene: Charge-Transfer Interaction and Remarkable High Ambipolar Transport Characteristics

A single crystal of a novel mixed-stack donor-acceptor complex formed by a tetracyanoquinodimethane derivative with an extended π-conjugated system and a sulfur-bridged annulene displays the highest ambipolar transport behavior among donor-acceptor complexes reported with electron and hole mobilities reaching up to 0.24 and 0.77 cm(2) V(-1) s(-1) , respectively.

Understanding the Charge Transport and Polarities in Organic Donor–Acceptor Mixed‐Stack Crystals: Molecular Insights from the Super‐Exchange Couplings

Charge transport and polarity in organic D-A mixed-stack crystals are examined in terms of super-exchange electronic couplings. When the super-exchange coupling is dominated by the interaction between donor HOMO and acceptor LUMO, ambipolar transport is achieved. Otherwise, involvement of other bridge orbitals can lead to unbalanced, even to unipolar transport in a special case that the HOMO-LUMO interaction vanishes.

Molecular dynamics simulations of the supramolecular assembly between an azobenzene-containing surfactant and α-cyclodextrin: role of photoisomerization.

Control of the self-assembly and disassembly at the molecular level has become a subject of increasing activity. The supramolecular assembly between a photoswitchable azobenzene-containing surfactant, AzoC10, and α-cyclodextrin that combines photochemistry and host-guest chemistry for a stimulus-responsive vesicle has been recently reported. To clarify the role of photoisomerization in the reversible assembly and disassembly, we present in this work atomistic molecular dynamics simulations of the host-guest complexation of AzoC10 with α-cyclodextrin. The results of simulation reveal that both cis- and trans-AzoC10 form the inclusion complexes with α-CD, but the binding modes are rather different. The azobenzene moiety of trans-AzoC10 is included at the center of the cavity of α-CD, whereas one of the phenyl rings of cis-AzoC10 is exposed to water and the other is included in the cavity of α-CD. The shuttling motion of α-CD over the long alkyl chain of cis-AzoC10 is observed in the simulations. The potentials of mean force calculated for AzoC10 to pass through the cavity of α-CD show that the host-guest assembly is basically downhill for trans-AzoC10, but an energy barrier has to be overcome for cis-AzoC10 to complex with α-CD.

Synthesis, optical properties, and helical self-assembly of a bivaline-containing tetraphenylethene

A chiral tetraphenylethene derivative with two valine-containing attachments (TPE-DVAL), was synthesized by Cu(I)-catalyzed azide-alkyne “click” reaction. The optical properties and self-assembling behaviours of TPE-DVAL were investigated. The molecule is non-emissive and circular dichroism (CD)-silent in solution, but shows strong fluorescence and Cotton effects in the aggregation state, demonstrating aggregation-induced emission (AIE) and CD (AICD) characteristics. TPE-DVAL exhibits good circularly polarized luminescence (CPL) when depositing on the surface of quartz to allow the evaporation of its 1,2-dichloroethane solution. SEM and TEM images of the molecule show that the molecule readily self-assembles into right-handed helical nanofibers upon the evaporation of its solvent of DCE. The molecular alignments and interactions in assembling process are further explored through XRD analysis and computational simulation. The driving forces for the formation of the helical fibers were from the cooperative effects of intermolecular hydrogen bonding, π-π interactions and steric effect.

Dramatic Differences in Aggregation-Induced Emission and Supramolecular Polymerizability of Tetraphenylethene-Based Stereoisomers

Geometric (Z)- and (E)-isomers play important but different roles in life and material science. The design of new (Z)-/(E)- isomers and study of their properties, behaviors, and interactions are crucially important in molecular engineering. However, difficulties with their separation and structure confirmation limit their structural diversity and functionality in scope. In the work described herein, we successfully synthesized pure isomers of ureidopyrimidinone-functionalized tetraphenylethenes ((Z)-TPE-UPy and (E)-TPE-UPy), featuring both the aggregation-induced emission characteristic of tetraphenylethene and the supramolecular polymerizability of ureidopyrimidinone. Their structures were confirmed by 2D COSY and NOESY NMR spectroscopies. The two isomers show distinct fluorescence in the aggregate state: (Z)-TPE-UPy exhibits green emission, while its (E)-counterpart is blue-emitting. The cavity formed by the two ureidopyrimidinone groups of (Z)-TPE-UPy makes it suitable for Hg2+ detection, and the high-molecular-weight polymers prepared from (E)-TPE-UPy can be used to fabricate highly fluorescent fibers and 2D/3D photopatterns from their chloroform solutions.

Ionization and Anion−π+ Interaction: A New Strategy for Structural Design of Aggregation-Induced Emission Luminogens

Recent years have witnessed the significant role of anion-π+ interactions in many areas, which potentially brings the opportunity for the development of aggregation-induced emission (AIE) systems. Here, a new strategy that utilized anion-π+ interactions to block detrimental π-π stacking was first proposed to develop inherent-charged AIE systems. Two AIE-active luminogens, namely, 1,2,3,4-tetraphenyloxazolium (TPO-P) and 2,3,5-triphenyloxazolium (TriPO-PN), were successfully synthesized. Comprehensive techniques such as single-crystal analysis, theoretical calculation, and conductivity measurement were used to illustrate the effects of anion-π+ interactions on the AIE feature. Their analogues tetraphenylfuran (TPF) and 2,4,5-triphenyloxazole (TriPO-C) without anion-π+ interactions suffered from the aggregation-caused emission quenching in the aggregate state, demonstrating the important role of anion-π+ interactions in suppressing π-π stacking. TriPO-PN was biocompatible and could specifically target lysosome in fluorescence turn-on and wash-free manners. This suggested that it was a promising contrast agent for bioimaging.

Multiscale Humidity Visualization by Environmentally Sensitive Fluorescent Molecular Rotors

Building humidity sensors possessing the features of diverse-configuration compatibility, and capability of measurement of spatial and temporal humidity gradients is of great interest for highly integrated electronics and wearable monitoring systems. Herein, a visual sensing approach based on fluorescent imaging is presented, by assembling aggregation-induced-emission (AIE)-active molecular rotors into a moisture-captured network; the resulting AIE humidity sensors are compatible with diverse applications, having tunable geometries and desirable architectures. The invisible information of relative humidity (RH) is transformed into different fluorescence colors that enable direct observation by the naked eyes based on the twisted intramolecular charge-transfer effect of the AIE-active molecular rotors. The resulting AIE humidity sensors show excellent performance in terms of good sensitivity, precise quantitative measurement, high spatial-temporal resolution, and fast response/recovery time. Their multiscale applications, such as regional environmental RH detection, internal humidity mapping, and sensitive human-body humidity sensing are demonstrated. The proposed humidity visualization strategy may provide a new insight to develop humidity sensors for various applications.

Real-time Monitoring of Hydrophobic Aggregation Reveals a Critical Role of Cooperativity in Hydrophobic Effect

The hydrophobic interaction drives nonpolar solutes to aggregate in aqueous solution, and hence plays a critical role in many fundamental processes in nature. An important property intrinsic to hydrophobic interaction is its cooperative nature, which is originated from the collective motions of water hydrogen bond networks surrounding hydrophobic solutes. This property is widely believed to enhance the formation of hydrophobic core in proteins. However, cooperativity in hydrophobic interactions has not been successfully characterized by experiments. Here, we quantify cooperativity in hydrophobic interactions by real-time monitoring the aggregation of hydrophobic solute (hexaphenylsilole, HPS) in a microfluidic mixer. We show that association of a HPS molecule to its aggregate in water occurs at sub-microsecond, and the free energy change is −5.8 to −13.6 kcal mol−1. Most strikingly, we discover that cooperativity constitutes up to 40% of this free energy. Our results provide quantitative evidence for the critical role of cooperativity in hydrophobic interactions.

A “clicked” porphyrin cage with high binding affinity towards fullerenes

A cage-structured receptor was synthesized in a facile “clicked” way and showed high affinity for fullerenes and differentiated rates of binding to C60 and C70.

Anion-Binding Properties of π-Electron Deficient Cavities in Bis(tetraoxacalix[2]arene[2]triazine): A Theoretical Study

The anion recognition by synthetic host molecules is an important theme in supramolecular chemistry. Bis(tetraoxacalix[2]arene[2]triazine) is a conformationally rigid cage molecule with three V-shaped clefts, each constituted by two electron-deficient triazine rings and two aryl C-H moieties. Its halide-binding properties are investigated in this work by quantum chemistry methods. The calculated Gibbs free energies display similar trends as the experimental observations. It has been shown that different types of noncovalent interactions including H-bond, anion-π, and lone-pair-π interactions are concurrent, leading to a cooperative effect. The respective contributions of the interactions to the overall stability are evaluated by using appropriate reference systems, with the anion-π interactions found to be as significant as the hydrogen bond interactions. In addition, in the presence of a water molecule, the stability of the ternary complexes has enhanced greatly in comparison with the binary complexes. Investigations of the solvent effect by the continuum solvent model show that the anion binding energies decrease with increasing solvent polarities. The weak halide binding energies in solution indicate that the reversible binding interactions with bis(tetraoxacalix[2]arene[2]triazine) can offer potential applications for anion transport in the membrane environment.