Shengbin Lei

Molecular and Supramolecular Networks on Surfaces: From Two-Dimensional Crystal Engineering to Reactivity

The invention of the scanning tunneling microscope has led to the visualization of molecules in real space on atomically flat conductive substrates. This has boosted research into supramolecular chemistry on surfaces. In this Review, we highlight recent developments in the design and functionality of supramolecular surface patterns, with special attention paid to those networks which are chiral or contain a high degree of porosity as well as to the reactivity, which is one of the most important recent developments in supramolecular surface chemistry.

Graphene-based polyaniline nanocomposites: preparation, properties and applications

Graphene is very popular in recent years, due to its unique electrical, thermal, mechanical, optical and electrochemical properties. With these useful advantages, graphene has been used as a substance to incorporate various kinds of functional materials. Among them, graphene-based polyaniline (PANI) nanocomposites have attracted a great deal of interest due to their new properties or enhanced performance during the past few years. This is because PANI is a useful conducting polymer that has been widely used for electronic, optical and electrochemical applications owing to its low cost, good environmental stability, interesting electroactivity, high pseudocapacitance and unusual doping/dedoping chemistry. This review discusses the current development of graphene-based PANI nanocomposites. After introduction of the properties of graphene, we summarize various methods to synthesize graphene-based PANI nanocomposites, as well as their enhanced properties. Finally, the applications of graphene-based PANI nanocomposites, such as supercapacitors, sensing platforms, fuel cells, solar cells, electrochromic devices, lithium ion batteries and so on, are described.

Molecular Clusters in Two-Dimensional Surface-Confined Nanoporous Molecular Networks: Structure, Rigidity, and Dynamics

The self-assembly of a series of hexadehydrotribenzo[12]annulene (DBA) derivatives has been investigated by scanning tunneling microscopy (STM) at the liquid/solid interface in the absence and presence of nanographene guests. In the absence of appropriate guest molecules, DBA derivatives with short alkoxy chains form two-dimensional (2D) porous honeycomb type patterns, whereas those with long alkoxy chains form predominantly dense-packed linear type patterns. Added nanographene molecules adsorb in the pores of the existing 2D porous honeycomb type patterns or, more interestingly, they even convert the guest-free dense-packed linear-type patterns into guest-containing 2D porous honeycomb type patterns. For the DBA derivative with the longest alkoxy chains (OC20H41), the pore size, which depends on the length of the alkoxy chains, reaches 5.4 nm. Up to a maximum of six nanographene molecules can be hosted in the same cavity for the DBA derivative with the OC20H41 chains. The host matrix changes its structure in order to accommodate the adsorption of the guest clusters. This flexibility arises from the weak intermolecular interactions between interdigitating alkoxy chains holding the honeycomb structure together. Diverse dynamic processes have been observed at the level of the host matrix and the coadsorbed guest molecules.

Site‐Selective Fabrication of Two‐Dimensional Fullerene Arrays by Using a Supramolecular Template at the Liquid‐Solid Interface

have been successfully used to direct theformation of ordered fullerene arrays. In this way theinterfullerene distance and symmetry of the arrangementaresolelydeterminedbythemoleculartemplateandcanbechanged by adjusting its structure. More importantly, inter-actions between fullerenes can also be modified with thisstrategy.Wehavedesignedandsynthesizedatetraacidicazoben-zene molecule NN4A (Figure1a) that exclusively formsKagomopennetworkswithtwotypesofcavitiesthathavedifferent size and symmetry at the liquid–solid interface.These cavities are capable of accommodating fullerenemolecules as guest species. Herein, we examine the siteselectivityofthenetworksfordifferentfullerenes,afeaturewhichhasnotbeenobservedforothersystemsatliquid–solidinterfaces.Azobenzenederivativesaretypicalphotochromiccompoundsthathaveawiderangeofpotentialapplications,including for optical switching, holographic storage, lightharvesting, long-term energy storage, and nonlinear opticalmaterials.

2D Networks of Rhombic-Shaped Fused Dehydrobenzo[12]annulenes: Structural Variations under Concentration Control

A series of alkyl- and alkoxy-substituted rhombic-shaped bisDBA derivatives 1a-d, 2a, and 2b were synthesized for the purpose of the formation of porous networks at the 1,2,4-trichlorobenzene (TCB)/graphite interface. Depending on the alkyl-chain length and the solute concentration, bisDBAs exhibit five network structures, three porous structures (porous A, B, and C), and two nonporous structures (nonporous D and E), which are attributed to their rhombic core shape and the position of the substituents. BisDBAs 1a and 1b with the shorter alkyl chains favorably form a porous structure, whereas bisDBAs 1c and 1d with the longer alkyl chains are prone to form nonporous structures. However, upon dilution, nonporous structures are typically transformed into porous ones, a trend that can be understood by the effect of surface coverage, molecular density, and intermolecular interactions on the systems enthalpy. Furthermore, porous structures are stabilized by the coadsorption of solvent molecules. The most intriguing porous structure, the Kagome pattern, was formed for all compounds at least to some extent, and the size of its triangular and hexagonal pores could be tuned by the alkyl-chain length. The present study proves that the concentration control is a powerful and general tool for the construction of porous networks at the liquid-solid interface.

Surface-Confined Crystalline Two-Dimensional Covalent Organic Frameworks via on-Surface Schiff-Base Coupling

We performed a co-condensation reaction between aromatic aldehyde and aromatic diamine monomers on a highly oriented pyrolytic graphite surface either at a solid/liquid interface at room temperature or in low vacuum with moderate heating. With this simple and moderate methodology, we have obtained surface-confined 2D covalent organic frameworks (COFs) with few defects and almost entire surface coverage. The single crystalline domain can extend to more than 1 μm(2). By varying the backbone length of aromatic diamines the pore size of 2D surface COFs is tunable from ∼1.7 to 3.5 nm. In addition, the nature of the surface COF can be modified by introducing functional groups into the aromatic amine precursor, which has been demonstrated by introducing methyl groups to the backbone of the diamine. Formation of small portions of bilayers was observed by both scanning tunneling microscopy (STM) and AFM, which clearly reveals an eclipsed stacking manner.

Electric driven molecular switching of asymmetric tris(phthalocyaninato) lutetium triple-decker complex at the liquid/solid interface.

Molecular structures are known to significantly impact the adsorption and assembling behavior of the adsorbates on surfaces. Precise control of the molecular orientation and ordering will enable us to tailor the physical and chemical properties of the molecular architectures. In this work, we present a strategy of attaching functional groups with dissimilar adsorption and assembling characteristics to the top and bottom phthalocyaninato moieties of a triple-decker complex, and orientational-dependent ordering of such molecules at the liquid/solid interface has been identified, which is attributed to the interaction of the intrinsic molecular dipole with the external electric field. In addition, isomerization of the noncentrosymmetric tris(phthalocyaninato) lutetium triple-decker complex has been revealed directly with STM and further confirmed by theoretical simulation. This approach provides a possible way for the preparation of organic films with switchable electronic and/or interface properties with external field.

One building block, two different nanoporous self-assembled monolayers: a combined STM and Monte Carlo study.

With the use of a single building block, two nanoporous patterns with nearly equal packing density can be formed upon self-assembly at a liquid-solid interface. Moreover, the formation of both of these porous networks can be selectively and homogenously induced by changing external parameters like solvent, concentration, and temperature. Finally, their porous properties are exploited to host up to three different guest molecules in a spatially resolved way.

Site-Selective Guest Inclusion in Molecular Networks of Butadiyne-Bridged Pyridino and Benzeno Square Macrocycles on a Surface

We present here the formation of a modular 2D molecular network composed of two different types of square-shaped butadiyne-bridged macrocycles, having intrinsic molecular voids, aligned alternately at the solid-liquid interface. Site-selective inclusion of a guest cation took place at every other molecular void in the molecular network with two different recognition sites.

Large All-Hydrocarbon Spoked Wheels of High Symmetry: Modular Synthesis, Photophysical Properties, and Surface Assembly

In a convergent modular synthesis, a very efficient pathway to shape-persistent molecular spoked wheels has been developed and applied according to the covalent-template concept. The structurally defined two-dimensional (2D) oligo(phenylene-ethynylene-butadiynylene)s (OPEBs) presented here are about 8 nm sized hydrocarbons of high symmetry. 48 alkyl chains attached to the molecular plane (hexyl and hexadecyl, respectively) guarantee a high solubility of the compounds. The structure and uniformity of these defined, stable, D(6h) symmetrical compounds is verified by MALDI-MS, GPC analysis, and high-temperature (HT) (1)H and (13)C NMR. Detailed photophysical measurements of nonaggregated molecules in solution (as confirmed by dynamic light scattering (DLS)) focus on the identification of chromophores by comparison with suitable model compounds. Moreover, time-resolved measurements including fluorescence lifetime and depolarization support the chromophore assignment and reveal the occurrence of intramolecular energy transfer. Scanning tunneling microscope (STM) characterization at the solid/liquid interface demonstrates the efficient self-assembly of the OPEBs into hexagonal 2D crystalline layers with a periodicity determined by both the size of the OPEB backbone and the length of peripheral side chains. Atomic force microscope (AFM) studies show a very different assembly behavior of the two spoked wheel molecules, on both graphite and mica. While the hexyl-substituted wheel can form stacked superstructures, hexadecyl groups prevent any ordering in the film aside from the monolayer directly in contact with the surface.