Showing papers by "Wenli Deng published in 2020"

Molecular trapping in two-dimensional chiral organic Kagomé nanoarchitectures composed of Baravelle spiral triangle enantiomers

Abstract: The supramolecular self-assembly of a push-pull dye is investigated using scanning tunneling microscopy (STM) at the liquid–solid interface. The molecule has an indandione head, a bithiophene backbone and a triphenylamine–bithiophene moiety functionalized with two carboxylic acid groups as a tail. The STM images show that the molecules adopt an “L” shape on the surface and form chiral Baravelle spiral triangular trimers at low solution concentrations. The assembly of these triangular chiral trimers on the graphite surface results in the formation of two types of chiral Kagome nanoarchitectures. The Kagome-α structure is composed of only one trimer enantiomer, whereas the Kagome-β structure results from the arrangement of two trimer enantiomers in a 1:1 ratio. These Kagome lattices are stabilized by intermolecular O-H···O hydrogen bonds between carboxylic acid groups. These observations reveal that the complex structure of the push-pull dye molecule leads to the formation of sophisticated two-dimensional chiral Kagome nanoarchitectures. The subsequent deposition of coronene molecules leads to the disappearance of the Kagome-β structure, whereas the Kagome-α structure acts as the host template to trap the coronene molecules. A thin film that spontaneously forms into complex geometric patterns can undergo molecular recognition interactions helpful for sensing small molecules. A team led by Xinrui Miao from the South China University of Technology in Guangzhou and Fabien Silly at the Universite Paris-Saclay in Gif sur Yvette, France, used scanning tunneling microscopy to understand how photoactive dyes commonly used in organic solar cells self-organize into assemblies. The team first modified the dyes with carboxylic acids, giving them a spiral structure and enhanced hydrogen bonding capabilities. Atomic-scale imaging of the molecules on graphite revealed that at certain concentrations, groups of dyes could lock together into triangular tiles. In turn, the tiles connected into symmetric lattices containing nanoscale pores. Certain lattices could trap aromatic hydrocarbons within their hexagonal pores. Push-pull dye molecules self-assemble into two 2D Kagome nanoarchitectures composed of a single or two chiral Baravelle spiral triangular trimer enantiomers. Only one of the two nanoarchitectures is able to trap coronene molecules.

Systematical Investigation of Chain Length Effect on the Melting Point of a Series of Bifunctional Anthraquinone Derivatives via X-ray Diffraction and Scanning Tunneling Microscopy

Abstract: Introducing a continuously changing alkyl chain is effective to modify the conjugated molecule, which is widely used in studying the diversity of two-dimensional (2D) self-assembly and the performa...

Halogen-Bond-Controlled Self-Assembly of Regioisomeric Phenanthridine Derivatives into Nanowires and Nanosheets

Abstract: The spectroscopic and photophysical properties of organic materials in the films are widely influenced by their molecular packing morphologies and intermolecular interactions. Here, regioisomeric p...

Concentration-Dependent Conformational Isomerization of Fluorenone-Based Polycatenar in 2D Polymorphic Self-Assembly

Abstract: A fluorenone-based polycatenar consisting of a central 2,7-bis((5-phenylthiophen-2-yl)ethynyl)-9-fluorenone core and −OCH2– linked 3,4,5-tris(dodecyloxy)benzoate unit at both sides (FTQ) has been s...

Structural Diversity and Phase Transition Control via Kinetics and Thermodynamics in Mixed Solvents: Two-Dimensional Self-Assembly at the Liquid/Solid Interface

Abstract: Structural diversity and phase transition in the field of two-dimensional self-assembly have gained immense attention because of their potential value in nanoscience and nanotechnology. We present ...

Conformation modification of terthiophene during the on-surface synthesis of pure polythiophene.

Abstract: On-surface coupling under ultra-high vacuum is employed as a versatile approach to synthesize pure polythiophene from a 5,5′′-dibromo-2,2′:5′,2′′-terthiophene (DBTT) precursor and the corresponding temperature-dependent stepwise reaction mechanism is systematically studied by scanning tunneling microscopy (STM). After thermal deposition of the precursor onto a Au(111) surface that is kept at room temperature, a triangle-like pattern and a linear self-assembled pattern are formed with different molecular coverages through Br⋯Br⋯S halogen bonds and Br⋯Br type-I contact bonds, respectively. In the self-assembled nanostructures, the thiophene units adopt trans-conformation. Mild annealing promotes the structural transition of both nanostructures into ordered zigzag organometallic linear chains with all-cis configured thiophene units connected through coordination bonds to the Au adatoms. Such conformational variety is easily recognized by STM, particularly in the case of DBTT-CH3 with the extra –CH3 signals. The covalently coupled products from the DBTT precursor are obtained by further annealing the organometallic intermediate at higher temperatures, which leads to the removal of Au atoms and the formation of ordered polymer chains and disordered polythiophene networks. Further characterization suggests that the reaction mechanism is associated with Ullmann-type coupling to form the ordered chains as well as Ullmann-type and dehydrogenative C–C coupling to fabricate cross-linked polymer networks. Compared with the on-surface synthesis process of DBTT on the Cu(111) surface, it can be confirmed that the Au adatoms are vital to synthesize polythiophene. These findings provide important insight into the reaction mechanism of on-surface synthesized pure polythiophene and on-surface coupling can potentially be applied to synthesize other functional conjugated polymers.

Halogen Bonds Fabricate 2D Molecular Self-Assembled Nanostructures by Scanning Tunneling Microscopy

Abstract: Halogen bonds are currently new noncovalent interactions due to their moderate strength and high directionality, which are widely investigated in crystal engineering. The study about supramolecular two-dimensional architectures on solid surfaces fabricated by halogen bonding has been performed recently. Scanning tunneling microscopy (STM) has the advantages of realizing in situ, real-time, and atomic-level characterization. Our group has carried out molecular self-assembly induced by halogen bonds at the liquid–solid interface for about ten years. In this review, we mainly describe the concept and history of halogen bonding and the progress in the self-assembly of halogen-based organic molecules at the liquid/graphite interface in our laboratory. Our focus is mainly on (1) the effect of position, number, and type of halogen substituent on the formation of nanostructures; (2) the competition and cooperation of the halogen bond and the hydrogen bond; (3) solution concentration and solvent effects on the molecular assembly; and (4) a deep understanding of the self-assembled mechanism by density functional theory (DFT) calculations.

Ordering self-assembly structures via intermolecular BrS interactions.

Abstract: Recent research studies have shown that the halogenated benzo[1,2-b:4,5-b']dithiophene (DTBDT) unit as a polymer donor exhibits high charge carrier mobility due to the well-ordered molecular packing and high crystallinity, which is meaningful for achieving highly efficient organic solar cells (OSCs). However, it is difficult to acquire the accurate packing information of polymer materials. Herein, we investigated the self-assembled behaviors of two DTBDT derivatives, 4,8-bis(4-octadecylthiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene (H-DTBDT) and 4,8-bis(5-bromo-4-octadecylthiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene (Br-DTBDT), to elucidate the effect of introducing a bromine atom on molecular packing structures by STM at the 1-phenyloctane/HOPG interface. It is observed that the H-DTBDT molecules exhibit a random arrangement along each lamella, while the Br-DTBDT molecules self-assemble into a highly ordered lamellar structure. Density functional theory (DFT) analysis combined with the topological properties of the electron density at the bond critical points revealed that the existence of weak intermolecular interactions of BrS facilitates the regular packing motif of Br-DTBDT molecules. The results helped us to understand that the BrS bond generally acted as the auxiliary force and can play the primary role in the construction of supramolecular nanostructures.

Halogen-Bond-Controlled Self-Assembly of Regioisomeric Phenanthridine Derivatives into Nanowires and Nanosheets

Abstract: The spectroscopic and photophysical properties of organic materials in the films are widely influenced by their molecular packing morphologies and intermolecular interactions. Here, regioisomeric phenanthridine derivatives were synthesized. The UV–vis spectra and scanning electron microscopy images show that these molecules can form different self-organizations in the films. Scanning tunneling microscopy and density functional theory calculations are utilized to reveal their intermolecular interactions by visualizing the molecular packing in the self-assembly adlayers. The different intermolecular Br···N halogen bonds, H···Br hydrogen bonds, and Br···Br type-II halogen bonds are the dominated factors to form the different nanostructures and different morphologies in the films. This work provides a new viewpoint to explore the “molecule-packing-properties” relationship in order to rationally control the properties of organic materials through designing the molecules.

Structural Insights into the Dual-Phase Emission Mechanism of Naphthalene Derivatives with Scanning Tunneling Microscopy, X-ray Diffraction, and Density Functional Theory Calculations

Abstract: Dual-phase (solution and solid-state) emissive luminophores are proved to have much broader application than aggregation-induced emission (AIE) and aggregation-caused quench (ACQ) in many applied f...

A simple and environmental strategy to separate and purify dye-contaminated emulsion using waste porous honeycomb cinder

Abstract: Numerous superwetting materials have been designed to separate water-in-oil emulsions, however, it still remains challenge to realize emulsion separation and dye adsorption simultaneously. In this ...