Supramolecular assembly at interfaces: formation of an extended two-dimensional coordinate covalent square grid network at the air-water interface

Synthesis, mixed-spin-state structure and Langmuir-Blodgett deposition of amphiphilic Fe(iii) quinolylsalicylaldiminate complexes

Designing and integrating Fe(iii)-based spin crossover (SCO) complexes onto substrates remains a challenging goal with only a handful of examples reported. In this work, we successfully synthesized and characterized three [Fe(qsal-OR)2]NO3 (qsal-OR = 5-alkoxy-2-[(8-quinolylimino)methyl]phenolate) complexes, in which R = C12H251, C16H332, and C22H453 to explore the impact of alkyl chain on the modulation of SCO activity and potential for self-assembly on a glass surface. The SCO is found to be gradual and incomplete in all cases, with the LS state more stabilised as the alkyl group shortens. We also demonstrate that all complexes form stable Langmuir films and achieve good transfer ratios to the glass surface, with 2 being the best in terms of stability. This paves the way for the SCO modulation of complexes in this class and the development of SCO devices.

2D Conjugated Polymer Thin Films for Organic Electronics: Opportunities and Challenges

2D conjugated polymers (2DCPs) possess extended in-plane π-conjugated lattice and out-of-plane π-π stacking, which results in enhanced electronic performance and potentially unique band structures. These properties, along with predesignability, well-defined channels, easy postmodification, and order structure attract extensive attention from material science to organic electronics. In this review, the recent advance in the interfacial synthesis and conductivity tuning strategies of 2DCP thin films, as well as their application in organic electronics is summarized. Furthermore, it is shown that, by combining topology structure design and targeted conductivity adjustment, researchers have fabricated 2DCP thin films with predesigned active groups, highly ordered structures, and enhanced conductivity. These films exhibit great potential for various thin-film organic electronics, such as organic transistors, memristors, electrochromism, chemiresistors, and photodetectors. Finally, the future research directions and perspectives of 2DCPs are discussed in terms of the interfacial synthetic design and structure engineering for the fabrication of fully conjugated 2DCP thin films, as well as the functional manipulation of conductivity to advance their applications in future organic electronics.

Bottom-up Synthesis of Nanosheets at Various Interfaces

Nanostructured materials with high aspect ratios have been widely studied for their unique properties. In particular, nanosheets have safety, dispersibility, and nanosized effects, and nanosheets with exceptionally small thicknesses exhibit unique properties. For non-exfoliable materials, the bottom-up nanosheet growth using various interfaces as templates have been investigated. This review article presents the synthesis of nanosheets at the interfaces and layered structure; it explains the features of each interface type, its advantages, and its uniqueness. The interfaces work as templates for nanosheet synthesis. We can easily use the liquid-liquid and gas-liquid interfaces as the templates; however, the thickness of nanosheets usually becomes thick because it allows materials to grow in thickness. The solid-gas and solid-liquid interfaces can prevent nanosheets from growing in thickness. However, the removal of template solids is required after the synthesis. The layered structures of various materials provide two-dimensional reaction fields between the layers. These methods have high versatility, and the nanosheets synthesized by these methods are thin. Finally, this review examines the key challenges and opportunities associated with scalable nanosheet synthesis methods for industrial production.

The Past and the Future of Langmuir and Langmuir-Blodgett Films

The Langmuir-Blodgett (LB) technique, through which monolayers are transferred from the air/water interface onto a solid substrate, was the first method to allow for the controlled assembly of organic molecules. With its almost 100 year history, it has been the inspiration for most methods to functionalize surfaces and produce nanocoatings, in addition to serving to explore concepts in molecular electronics and nanoarchitectonics. This paper provides an overview of the history of Langmuir monolayers and LB films, including the potential use in devices and a discussion on why LB films are seldom considered for practical applications today. Emphasis is then given to two areas where these films offer unique opportunities, namely, in mimicking cell membrane models and exploiting nanoarchitectonics concepts to produce sensors, investigate molecular recognitions, and assemble molecular machines. The most promising topics for the short- and long-term prospects of the LB technique are also highlighted.

Structure–property relations of amphiphilic poly(furfuryl glycidyl ether)-block-poly(ethylene glycol) macromonomers at the air–water interface

Structure–property relations of poly(furfuryl glycidyl ether)-block-poly(ethylene glycol) macromonomers at the air–water interface are studied with a Langmuir film balance.

Materials nanoarchitectonics at two-dimensional liquid interfaces

Much attention has been paid to the synthesis of low-dimensional materials from small units such as functional molecules. Bottom-up approaches to create new low-dimensional materials with various functional units can be realized with the emerging concept of nanoarchitectonics. In this review article, we overview recent research progresses on materials nanoarchitectonics at two-dimensional liquid interfaces, which are dimensionally restricted media with some freedoms of molecular motion. Specific characteristics of molecular interactions and functions at liquid interfaces are briefly explained in the first parts. The following sections overview several topics on materials nanoarchitectonics at liquid interfaces, such as the preparation of two-dimensional metal-organic frameworks and covalent organic frameworks, and the fabrication of low-dimensional and specifically structured nanocarbons and their assemblies at liquid-liquid interfaces. Finally, interfacial nanoarchitectonics of biomaterials including the regulation of orientation and differentiation of living cells are explained. In the recent examples described in this review, various materials such as molecular machines, molecular receptors, block-copolymer, DNA origami, nanocarbon, phages, and stem cells were assembled at liquid interfaces by using various useful techniques. This review overviews techniques such as conventional Langmuir-Blodgett method, vortex Langmuir-Blodgett method, liquid-liquid interfacial precipitation, instructed assembly, and layer-by-layer assembly to give low-dimensional materials including nanowires, nanowhiskers, nanosheets, cubic objects, molecular patterns, supramolecular polymers, metal-organic frameworks and covalent organic frameworks. The nanoarchitecture materials can be used for various applications such as molecular recognition, sensors, photodetectors, supercapacitors, supramolecular differentiation, enzyme reactors, cell differentiation control, and hemodialysis.

Driving Coordination Polymer Monolayer Formation by Competitive Reactions at the Air/Water Interface

We have developed a novel approach enabling us to follow and facilitate the formation of two-dimensional coordination polymer monolayers directly at the air/water interface without the need of complex instrumentation. The method is based on the use of a surface active ligand that, when spread at the air/water interface, progressively undergoes hydrolysis with consequent gradual decrease in surface pressure. Notably, if the aqueous subphase contains metal ions capable of coordinating the ligand, coordination competes with hydrolysis, resulting in a lower surface pressure decrease. As a consequence, the formation of the coordination polymer monolayer can be verified simply by surface pressure measurements. Competition between hydrolysis and coordination was investigated as a function of the main experimental parameters affecting the two reactions, enabling the formation of stable coordination polymer monolayers with controlled density. Finally, the formation of continuous rigid 2D layers was confirmed by compression isotherms and ex situ morphological characterization. This work will simplify the verification of coordination polymer monolayer formation; thus, it will boost the synthesis of novel and innovative 2D materials.

Photomagnetic molecular and extended network Langmuir–Blodgett films based on cyanide bridged molybdenum–copper complexes

The present manuscript describes two types of cyanide bridged molybdenum–copper photomagnetic films obtained by the Langmuir–Blodgett technique.

Prussian blue analogues of reduced dimensionality

Mixed-valence polycyanides (Prussian Blue analogues) possess a rich palette of properties spanning from room-temperature ferromagnetism to zero thermal expansion, which can be tuned by chemical modifications or the application of external stimuli (temperature, pressure, light irradiation). While molecule-based materials can combine physical and chemical properties associated with molecular-scale building blocks, their successful integration into real devices depends primarily on higher-order properties such as crystal size, shape, morphology, and organization. Herein a study of a new reduced-dimensionality system based on Prussian Blue analogues (PBAs) is presented. The system is built up by means of a modified Langmuir-Blodgett technique, where the PBA is synthesized from precursors in a self-limited reaction on a clay mineral surface. The focus of this work is understanding the magnetic properties of the PBAs in different periodic, low-dimensional arrangements, and the influence of the "on surface" synthesis on the final properties and dimensionality of the system.

Cyanide-bridged NiCr and alternate NiFe-NiCr magnetic ultrathin films on functionalized Si(100) surface

Sequential growth in solution (SGS) was performed for the magnetic cyanide-bridged network obtained from the reaction of Ni(H(2)O)(2+) and Cr(CN)(6)(3-) (referred to as NiCr) on a Si(100) wafer already functionalized by a Ni(II) complex. The growth process led to isolated dots and a low coverage of the surface. We used the NiFe network as a template to improve the growth of the magnetic network. We elaborated alternate NiFe (paramagnetic)-NiCr (ferromagnetic) ultrathin films around 6 nm thick. The magnetic behaviour confirmed the alternate structure with the ferromagnetic zones isolated between the paramagnetic ones since the evolution of the blocking temperature is consistent with the evolution of the layers' thickness expected from the SGS process.

Dual lanthanide role in the designed synthesis of hollow metal coordination (Prussian Blue analogue) nanocages with large internal cavity and mesoporous cage

Prussian Blue (PB) analogue metal coordination nanocages comprised of mesoporous walls (ca. 3.5 nm pore width) encapsulating a cavity approaching ca. 100 nm in diameter (surfactant free) are presented as an advance in rational metal coordination polymer nanostructure design. The synthesis employs lanthanide ions (Gd(3+) or Er(3+)) which function initially as peripheral coordination crosslinkers of metallo-surfactant templated miniemulsion droplets, and, subsequently, as promoters in the removal of the organic component of those surfactants via metal-assisted ester hydrolysis. The success of this synthetic strategy relies entirely on the periphery coordination event occurring prior to the ester hydrolysis surfactant removal step. Crucially, this one-pot sequential synthesis was achieved using a newly developed metallo-surfactant designed to have a reduced ester hydrolysis rate. Syntheses of this innovative metallo-surfactant, intermediary PB analogue coordination polymer organo-nanoshells and the subsequent conversion to hollow metal coordination nanocages are fully characterised using a wide variety of techniques, including TEM, SEM, EFTEM, EDX, TGA, WAXD, NMR, N(2) adsorption, etc., and represent the first designed synthesis of hollow metal coordination nanocages containing a large nanoscale cavity (wall of hollow nanosphere is mesoporous; hence nanocage).

Prussian blue coordination polymer nanobox synthesis using miniemulsion periphery polymerization (MEPP)

Metal coordination polymer nanoboxes are reported for the first time. Initially spherical miniemulsion droplet templates were transformed to hollow cubic crystalline nanostructures via a miniemulsion periphery polymerization conducted under benign thermal and chemical conditions.

Two-dimensional nanoarchitectonics based on self-assembly

Top-down nanofabrication techniques, especially photolithography, have advanced nanotechnology to a point where system-process integration with bottom-up self-assembly is now required. Because most lithographic techniques are constrained to two-dimensional planes, investigation of integrated self-assembly systems should focus on two-dimensional organization. In this review, research on two-dimensional nanoartchitectonics is classified and summarized according to the type of interface used. Pattern formation following deposition of vaporized molecules onto a solid surface can be analyzed with high structural precision using scanning probe microscopy under ultra high vacuum. Transitions of adsorbed phases and adjustment of pattern mismatch by conformational changes of adsorbed molecules are discussed, in addition to the forces constraining pattern formation, i.e., two-dimensional hydrogen bond networks, van der Waals forces, and molecule-surface interactions. Molecular deposition at a liquid-solid interface broadens the range of molecules that can be investigated. The more complex molecules discussed in this work are C(60)-fullerene derivatives and designer DNA strands. Gas-liquid interfaces, e.g. between air and water, allow dynamic formations that can adjust to molecular conformational changes. In this case, any resulting patterns can be modulated by varying conditions macroscopically. Using flexible molecules at the fluid air-water interface also permits dynamic operation of molecular machines by macroscopic mechanical motion, thus enabling, hand-operated nanotechnology.