Recently we assisted a strong renewed interest in the fascinating field of molecular spin crossover complexes by (1) the emergence of nanosized spin crossover materials through direct synthesis of coordination nanoparticles and nanopatterned thin films as well as by (2) the use of novel sophisticated high spatial and temporal resolution experimental techniques and theoretical approaches for the study of spatiotemporal phenomena in cooperative spin crossover systems. Besides generating new fundamental knowledge on size-reduction effects and the dynamics of the spin crossover phenomenon, this research aims also at the development of practical applications such as sensor, display, information storage and nanophotonic devices. In this critical review, we discuss recent work in the field of molecule-based spin crossover materials with a special focus on these emerging issues, including chemical synthesis, physical properties and theoretical aspects as well (223 references).

Molecular spin crossover phenomenon: recent achievements and prospects

https://www.pnas.org/content/pnas/90/5/1635.full.pdf

Supramolecular chemistry.

Supramolecular Polymers: Historical Development, Preparation, Characterization, and Functions.

Creating functional electrical circuits using individual or ensemble molecules, often termed as “molecular-scale electronics”, not only meets the increasing technical demands of the miniaturization of traditional Si-based electronic devices, but also provides an ideal window of exploring the intrinsic properties of materials at the molecular level. This Review covers the major advances with the most general applicability and emphasizes new insights into the development of efficient platform methodologies for building reliable molecular electronic devices with desired functionalities through the combination of programmed bottom-up self-assembly and sophisticated top-down device fabrication. First, we summarize a number of different approaches of forming molecular-scale junctions and discuss various experimental techniques for examining these nanoscale circuits in details. We then give a full introduction of characterization techniques and theoretical simulations for molecular electronics. Third, we highlig...

Molecular-Scale Electronics: From Concept to Function

Two-dimensional (2D) metal–organic framework (MOF) nanosheets are attracting increasing research attention due to their unique properties originating from their ultrathin thickness, large surface area and high surface-to-volume atom ratios. Many great advances have been made in the synthesis and application of 2D MOF nanosheets over the past few years. In this review, we summarize the recent advances in the synthesis of 2D MOF nanosheets by using top-down methods, e.g. sonication exfoliation, mechanical exfoliation, Li-intercalation exfoliation and chemical exfoliation, and bottom-up methods, i.e. interfacial synthesis, three-layer synthesis, surfactant-assisted synthesis, modulated synthesis, and sonication synthesis. In addition, the recent progress in 2D MOF nanosheet-based nanocomposites is also briefly introduced. The potential applications of 2D MOF nanosheets in gas separation, energy conversion and storage, catalysis, sensors and biomedicine are discussed. Finally, we give our personal insights into the challenges and opportunities for the future research of 2D MOF nanosheets and their composites.

Two-dimensional metal-organic framework nanosheets: synthesis and applications.

because the functions of thenanoobjects are dependent on their shape and dimensions. Inthe area of organic nanophotonics in particular, the confine-ment of optical waves in shape-shifting organic nanostruc-tures is interesting because of their potential use in “smart”nanooptical devices, such as optical waveguides, photonicdetectors, and optical sensors.Until now, no methods for the fabrication of reversiblyshape-shifting organic nanostructures that have dimension-ally dependent optical waveguiding properties have beenavailable. Most of the reported organic waveguides havedefined shapes

Reversibly Shape‐Shifting Organic Optical Waveguides: Formation of Organic Nanorings, Nanotubes, and Nanosheets

We report on theoretical and experimental work involving a particular molecular switch, an [FeII(L)2]2+ complex, that utilizes a spin transition (“crossover”). The hallmark of this transition is a change of the spin of the metal ion, SFe=0 to SFe=2, at fixed oxidation state of the Fe ion. Combining density functional theory and first principles calculations, we demonstrate that within a single molecule this transition can be triggered by charging the ligands. In this process the total spin of the molecule, combining metal ion and ligands, crosses over from S=0 to S=1. Three-terminal transport through a single molecule shows indications of this transition induced by electric gating. Such an electric field control of the spin transition allows for a local, fast, and direct manipulation of molecular spins, an important prerequisite for molecular spintronics.

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Electrical control over the Fe(II) spin crossover in a single molecule: Theory and experiment

Micro- and Nanopatterning of Spin-Transition Compounds into Logical Structures

We present the one-dimensional optical-waveguiding crystal dithieno[3,2-a:2',3'-c]phenazine with a high aspect ratio, high mechanical flexibility, and selective self-absorbance of the blue part of its fluorescence (FL). While macrocrystals exhibit elasticity, microcrystals deposited at a glass surface behave more like plastic crystals due to significant surface adherence, making them suitable for constructing photonic circuits via micromechanical operation with an atomic-force-microscopy cantilever tip. The flexible crystalline waveguides display optical-path-dependent FL signals at the output termini in both straight and bent configurations, making them appropriate for wavelength-division multiplexing technologies. A reconfigurable 2×2-directional coupler fabricated via micromanipulation by combining two arc-shaped crystals splits the optical signal via evanescent coupling and delivers the signals at two output terminals with different splitting ratios. The presented mechanical micromanipulation technique could also be effectively extended to other flexible crystals.

Mechanophotonics: Flexible Single-Crystal Organic Waveguides and Circuits.

Nano/micro scale passive organic optical waveguides, which are self-assembled from tailor made organic molecules, are one of the less studied branches of organic photonics. This perspective article is primarily focused on the research work related to one dimensional (1D) passive organic optical waveguides. In the beginning, a brief theory of organic waveguides, recent works on active organic waveguides and attempts towards fabrication of integrated photonic components and circuits will be discussed. Later more focus will be given to passive organic wave guiding materials derived from 1D hexagonal submicrotubes, parallelepipedic nanotubes, shape shifting organic structures and paramagnetic tubes. By using laser ablation techniques, the polishing of organic tube tips, the precise control of the light propagation distance and the creation of multiple optical outputs will be discussed. This perspective also highlights some noteworthy applications of passive organic waveguides in remote sensing, excitation and defect identification. The end of this article concludes with the potential of passive organic optical waveguides in future organic nanophotonics.

Rajadurai Chandrasekar

Papers

Reversibly Shape‐Shifting Organic Optical Waveguides: Formation of Organic Nanorings, Nanotubes, and Nanosheets

Electrical control over the Fe(II) spin crossover in a single molecule: Theory and experiment

Micro- and Nanopatterning of Spin-Transition Compounds into Logical Structures

Mechanophotonics: Flexible Single-Crystal Organic Waveguides and Circuits.

Organic photonics: prospective nano/micro scale passive organic optical waveguides obtained from π-conjugated ligand molecules.