Chain-Length Effects on Molecular Conformation in and Chirality of Self-Assembled Monolayers of Alkoxylated Benzo[c]cinnoline Derivatives on Highly Oriented Pyrolytic Graphite

Synthesis of trifluoroethoxy/aryloxy cinnolines, cinnolinones and indazoles from o-alkynylanilines via metal-free diazotization reagent

A facile and user-friendly protocol for the synthesis of trifluoroethoxy/aryloxy cinnolines, cinnolinones and indazoles from o-alkynylaniline in good-to-excellent yields has been developed using a metal-free diazotization reagent (a combination of BF3·OEt2 and TBN). The methodology has been further extended to construct bis-cinnolinones and for the chemoselective synthesis of N-propargylated cinnolinones.

Hydrazine-Directed Rh(III) Catalyzed (4+2) Annulation with Sulfoxonium Ylides: Synthesis and Photophysical Properties of Dihydrocinnolines

We herein report hydrazine-directed, Rh(III) catalyzed (4+2) annulation of N-alkyl aryl hydrazines with sulfoxonium ylides as a safe carbene precursor. The reaction shows excellent functional group tolerance with broad substrate...

Synthesis of new azobenzo[c]cinnolines and investigation of electronic spectra and spectroelectrochemical behaviours

A series of disazobenzo[c]cinnoline dyes was prepared by coupling reaction of 3,8-dihydroxybenzo[c]cinnoline with diazotised aromatic amines. The structures of these dyes were confirmed using UV-Vis, FTIR, ¹H NMR, LC-MS/MS and LC-MS/TOF spectroscopic techniques. ¹³C NMR, ¹³C-DEPT, ¹H-¹H COSY, ¹H-¹³C HMQC and ¹H-¹³C HMBC spectra of dye 12 were demonstrated in this study. In addition, the effects of the substituent attached to the phenyl ring, solvent and acid-base on the UV-Vis spectra of the dyes were investigated. Besides, voltammetric and spectroelectrochemical behaviours of four disazobenzo[c]cinnolines (2, 8, 11 and 13) in acetonitrile (ACN) solution were also evaluated. It was observed that the disazobenzo[c]cinnoline derivatives indicated reversible voltammetric behaviour in acetonitrile-tetrabutylammonium perchlorate (ACN-TBAP) solution. A square-wave potential step method coupled with optical spectroscopy was used to probe switching times and optic contrast of the dyes.

Engineering Long-Range Order in Supramolecular Assemblies on Surfaces: The Paramount Role of Internal Double Bonds in Discrete Long-Chain Naphthalenediimides

Achieving long-range order with surface-supported supramolecular assemblies is one of the pressing challenges in the prospering field of non-covalent surface functionalization. Having access to defect-free on-surface molecular assemblies will pave the way for various nanotechnology applications. Here we report the synthesis of two libraries of naphthalenediimides (NDIs) symmetrically functionalized with long aliphatic chains (C₂₈ and C₃₃) and their self-assembly at the 1-phenyloctane/highly oriented pyrolytic graphite (1-PO/HOPG) interface. The two NDI libraries differ by the presence/absence of an internal double bond in each aliphatic chain (unsaturated and saturated compounds, respectively). All molecules assemble into lamellar arrangements, with the NDI cores lying flat and forming 1D rows on the surface, while the carbon chains separate the 1D rows from each other. Importantly, the presence of the unsaturation plays a dominant role in the arrangement of the aliphatic chains, as it exclusively favors interdigitation. The fully saturated tails, instead, self-assemble into a combination of either interdigitated or non-interdigitated diagonal arrangements. This difference in packing is spectacularly amplified at the whole surface level and results in almost defect-free self-assembled monolayers for the unsaturated compounds. In contrast, the monolayers of the saturated counterparts are globally disordered, even though they locally preserve the lamellar arrangements. The experimental observations are supported by computational studies and are rationalized in terms of stronger van der Waals interactions in the case of the unsaturated compounds. Our investigation reveals the paramount role played by internal double bonds on the self-assembly of discrete large molecules at the liquid/solid interface.

Enantiomer surface chemistry: conglomerate versus racemate formation on surfaces

Research on surface chirality is motivated by the need to develop functional chiral surfaces for enantiospecific applications. While molecular chirality in 3D has been the subject of study for almost two centuries, many aspects of 2D chiral surface chemistry have yet to be addressed. In 3D, racemic mixtures of chiral molecules tend to aggregate into racemate (molecularly heterochiral) crystals much more frequently than conglomerate (molecularly homochiral) crystals. Whether chiral adsorbates on surfaces preferentially aggregate into heterochiral rather than homochiral domains (2D crystals or clusters) is not known. In this review, we have made the first attempt to answer the following question based on available data: in 2D racemic mixtures adsorbed on surfaces, is there a clear preference for homochiral or heterochiral aggregation? The current hypothesis is that homochiral packing is preferred on surfaces; in contrast to 3D where heterochiral packing is more common. In this review, we present a simple hierarchical scheme to categorize the chirality of adsorbate-surface systems. We then review the body of work using scanning tunneling microscopy predominantly to study aggregation of racemic adsorbates. Our analysis of the existing literature suggests that there is no clear evidence of any preference for either homochiral or heterochiral aggregation at the molecular level by chiral and prochiral adsorbates on surfaces.

Steering on-surface reactions with self-assembly strategy

The control of assembly structures that subsequently help achieve viable functionalities has been one of the key motivations for the exploration of surface molecular assembly. In terms of its functionality and applicability, the assembly is explored as a strategy to steer on-surface reactions primarily by two methods: assembly-assisted and assembly-involved reactions. The functions of the self-assembly strategy are threefold: tweaking reaction selectivities, steering reaction pathways, and directing reaction sites. The governing principle herein is that the assembly strategy can apply a surface confinement effect that affects the energy barrier and pre-exponential factor of the Arrhenius equation for the dynamics of the target reaction. Development of such a strategy may reveal new routes to steer on-surface reactions and even single molecule properties in surface chemistry.

Two side chains, three supramolecules: exploration of fluorenone derivatives towards crystal engineering

Structural diversity obtained through two-dimensional molecular self-assembly induced by the chain length effect has gained immense attention, not only because of its significance in crystal engineering but also for its potential application in nanoscience and nanotechnology. Three kinds of fluorenone derivative, named F-C₇C₇, F-C₁₄C₇, and F-C₁₄C₁₄, were synthesized and used for systematic exploration of their crystalline difference. At first, scanning electron microscopy and X-ray powder diffraction were performed to investigate their differences in morphology and three-dimensional crystal structure. Then scanning tunneling microscopy experiments were conducted to compare the self-assembled monolayers. Moreover, different solvents were used to repeatedly investigate the occurrence of structural diversity. F-C₇C₇ could not self-assemble into a stable monolayer on the graphite surface under ambient conditions due to its weak molecule-substrate interaction. F-C₁₄C₇ was observed to self-assemble into twist, plier-like, octamer-curve, and random structures in 1-octanoic acid, 1-phenyloctane, n-tetradecane, and dichloromethane, respectively. However, when the same solvents were used and at similar concentrations, the F-C₁₄C₁₄ molecules were arranged into interval, mixed, linear, and plier-like configurations. These self-assembled nanopatterns formed under the driving forces of dipole-dipole interactions, hydrogen bonds, and chain-chain, molecule-substrate, and molecule-solvent van der Waals interactions. Furthermore, from the viewpoint of thermal analysis, differential scanning calorimetry, as well as polarized optical microscopy, was performed to further elucidate the difference between these three compounds in the solid and liquid crystal states. The present system is believed to provide understanding of how the chain length effect induces different crystalline properties, and to open up the possibility of fabricating diverse self-assembled networks for crystal engineering.

Turning off the majority-rules effect in two-dimensional hierarchical chiral assembly by introducing a chiral mismatch

Understanding the mechanism in chiral transmission from a single molecule to a supramolecular level is fundamentally important to decipher the nonlinear amplification effect in the two-dimensional (2D) chiral assembly process. In this contribution, we report on the dramatically different nonlinear amplification effect in the chiral co-adsorber induced homochiral assemblies constructed by a series of homologous achiral building blocks on the graphite surface under control of the majority-rules principle. Homologous hexagonal networks are formed for 5-(benzyloxy)-isophthalic acid (BIC) derivatives with different alkyl lengths. While globally homochiral monolayers of BIC-C6 or BIC-C16 can be obtained by using a mixture of chiral co-adsorber 2-octanol with a small enantiomeric excess, such majority-rules principle based nonlinear chiral amplification is inoperative for the assembly of BIC-C10. Molecular mechanistic analysis indicates that BIC-C10 assembly can accommodate a chiral mismatched motif to form long-range ordered but short-range disordered crystalline networks, leading to the co-adsorption of enantiomers without enantioselectivity. The present results shed important insights into the significance of chirality mismatch during chiral transmission and benefit the understanding of chiral communication in a surface monolayer.

Fabrication of chiral networks for a tri-substituted anthraquinone derivative using molecular self-assembly

Chiral structures are recorded, with the adsorption of an achiral anthraquinone derivative and co-adsorption of achiral solvent on an achiral surface. Dimer, trimer and tetramer aggregations are observed while only the tetramer-dimer combination constructs the whole monolayer, and the formation mechanism is explained from the thermodynamic and kinetic viewpoints.

Expedient synthesis of new cinnoline diones by Ru-catalyzed regioselective unexpected deoxygenation-oxidative annulation of propargyl alcohols with phthalazinones and pyridazinones

Ruthenium-catalyzed simple, cascade and one-pot synthesis of cinnoline-fused diones has been carried out by the C–H activation of phthalazinones/pyridazinones.

Structural transition control between dipole–dipole and hydrogen bonds induced chirality and achirality

This study presents efficient strategies on manipulation of hydrogen bonds and dipole–dipole induced chiral and achiral self-assembly nanostructures.

Side chain position, length and odd/even effects on the 2D self-assembly of mono-substituted anthraquinone derivatives at the liquid/solid interface

This work provides efficient methods for regulating self-assembled structures by changing the position, length and odd/even properties of the side chains.

Patterned monolayer self-assembly programmed by side chain shape: four-component gratings

A molecular recognition strategy based on alkadiyne side chain shape is used to self-assemble a four-component, 1D-patterned monolayer at the solution-HOPG interface. The designed monolayer unit cell contains six molecules and spans 23 nm × 1 nm. The unit cell's internal structure and packing are driven by complementary shapes and lengths of six different alkadiyne side chains. A solution of the four compounds on HOPG self-assembles monolayers (i) comprised, almost entirely, of the intended unit cell, (ii) exhibiting patterned domains spanning 10(4) nm(2), and (iii) which are sufficiently robust that patterned domains survive solvent rinsing and drying. The patterned monolayer affords 1D-feature spacings ranging from 3.3 to 23 nm. The results demonstrate the remarkable selectivity afforded by molecular recognition based on alkadiyne side chain shape and the ability to program highly complex 1D-patterns in self-assembled monolayers.

In situ STM evidence for the adsorption geometry of three N-heteroaromatic thiols on Au(111)

The electrochemical behavior of three heteroaromatic thiols (MBs) (2-mercaptobenzimidazole (MBI), 2-mercaptobenzothiazole (MBT), and 2-mercaptobenzoxazole (MBO)) on a Au(111) surface has been investigated by electrochemical scanning tunneling microscopy (ECSTM) and cyclic voltammetry (CV) in 0.1 M HClO(4) solution. All three thiols form oriented molecular cluster lines along the reconstruction line direction at 0.55 V. With the electrode potential shifting negatively, the molecules undergo a disordered-ordered structural transition. Molecularly resolved STM images show that all three molecules form striped adlayers in the desorption region on the Au(111) surface. The different heteroatoms in the heteroaromatic rings result in different electrochemical behavior of the MB self-assembled monolayers (SAMs). MBI, MBT, and MBO are proposed to interact with the substrate via the S-Au bonds from thiol group and the coordination interaction of N, S, and O with the substrate from the heteroaromatic ring, respectively. These results provide direct evidence of the electrochemical behavior and the adlayer structures of MB SAMs on the Au electrode.

Nanopatterning of donor/acceptor hybrid supramolecular architectures on highly oriented pyrolytic graphite: a scanning tunneling microscopy study

Hybrid supramolecular architectures have been fabricated with acceptor 1,4-bis(4-pyridylethynyl)-2,3-bis-dodecyloxy-benzene (PBP) and donor 2,6-bis(3,4,5-tris-dodecyloxy-phenyl)dithieno[3,2-b:2',3'-d]thiophene (DTT) compounds on highly oriented pyrolytic graphite (HOPG) surfaces, and their structures and molecular conductance are characterized by scanning tunneling microscopy/spectroscopy (STM/STS). Stable, one-component adlayers of PBP and DTT are also investigated. The coadsorption of two-component mixtures of PBP and DTT results in a variety of hybrid nanopattern architectures that differ from those of their respective one-component surface assemblies. Adjusting the acceptor/donor molar ratio in mixed adlayer assemblies results in dramatic changes in the structure of the hybrid nanopatterns. STS measurements indicate that the HOMO and LUMO energy levels of PBP and DTT on an HOPG surface are relatively insensitive to changes in the hybrid supramolecular architectures. These results provide important insight into the design and fabrication of two-dimensional hybrid supramolecular architectures.