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Fluorescent plastically bendable crystals are a promising alternative to silicon‐based materials for fabricating photonic integrated circuits, owing to their optical attributes and mechanical compliance. Mechanically bendable plastic organic crystals are rare. Their formation requires anisotropic intermolecular interactions and slip planes in the crystal lattice. This work presents three fluorescent plastically bendable crystalline materials namely, 2‐((E)‐(6‐methylpyridin‐2‐ylimino)methyl)‐4‐chlorophenol (SB1), 2‐((E)‐(6‐methylpyridin‐2‐ylimino)methyl)‐4‐bromophenol (SB2), and 2‐((E)‐(6‐Bromopyridin‐2‐ylimino)methyl)‐4‐bromophenol (SB3) molecules. The crystal plasticity in response to mechanical stress facilitates the fabrication of various monolithic and hybrid (with a tip‐to‐tip coupling) photonic circuits using mechanical micromanipulation with an atomic force microscope cantilever tip. These plastically bendable crystals act as active (self‐guiding of fluorescence) and passive waveguides both in straight and extremely bent (U‐, J‐, and O‐shaped) geometries. These microcircuits use active and passive waveguiding principles and reabsorbance and energy‐transfer mechanisms for their operation, allowing input‐selective and direction‐specific signal transduction. [ABSTRACT FROM AUTHOR]

Flexible organic crystals (elastic and plastic) are important materials for optical waveguides, tunable optoelectronic devices, and photonic integrated circuits. Here, we present highly elastic organic crystals of a Schiff base, 1‐((E)‐(2,5‐dichlorophenylimino)methyl)naphthalen‐2‐ol (1), and an azine molecule, 2,4‐dibromo‐6‐((E)‐((E)‐(2,6‐dichlorobenzylidene)hydrazono)methyl)phenol (2). These microcrystals are highly flexible under external mechanical force, both in the macroscopic and the microscopic regimes. The mechanical flexibility of these crystals arises as a result of weak and dispersive C−H⋅⋅⋅Cl, Cl⋅⋅⋅Cl, Br⋅⋅⋅Br, and π⋅⋅⋅π stacking interactions. Singly and doubly‐bent geometries were achieved from their straight shape by a micromechanical approach using the AFM cantilever tip. Crystals of molecules 1 and 2 display a bright‐green and red fluorescence (FL), respectively, and selective reabsorption of a part of their FL band. Crystals 1 and 2 exhibit optical‐path‐dependent low loss emissions at the termini of crystal in their straight and even in extremely bent geometries. Interestingly, the excitation position‐dependent optical modes appear in both linear and bent waveguides of crystals 1 and 2, confirming their light‐trapping ability. [ABSTRACT FROM AUTHOR]

Single crystals of optoelectronic materials that respond to external stimuli, such as mechanical, light, or heat, are immensely attractive for next generation smart materials. Here we report single crystals of a green fluorescent protein (GFP) chromophore analogue with irreversible mechanical bending and associated unusual enhancement of the fluorescence, which is attributed to the strained molecular packing in the perturbed region. Soft crystalline materials with such fluorescence intensity modulations occurring in response to mechanical stimuli under ambient pressure conditions will have potential implications for the design of technologically relevant tunable fluorescent materials. [ABSTRACT FROM AUTHOR]

Ductility is a common phenomenon in many metals but is difficult to achieve in molecular crystals. Organic crystals bend plastically on one or two face‐specific directions but fracture when stressed in any other arbitrary directions. An exceptional metal‐like ductility and malleability in the isomorphous crystals of two globular molecules, BH3NMe3 and BF3NMe3, is reported, with characteristic tensile stretching, compression, twisting, and thinning. The mechanically deformed samples, which transition to lower symmetry phases, retain good long‐range order amenable to structure determination by single‐crystal X‐ray diffraction. Molecules in these high‐symmetry crystals interact through electrostatic forces (B−−N+) to form columnar structures with multiple slip planes and weak dispersive forces between columns. On the other hand, the limited number of facile slip planes and strong dihydrogen bonding in BH3NHMe2 negates ductility. Our study has implications for the design of soft ferroelectrics, solid electrolytes, barocalorics, and soft robotics. [ABSTRACT FROM AUTHOR]

Die mechanische Flexibilität von kovalenten Einkristallen ist ein faszinierendes und wenig verstandenes Phänomen. Wir stellen hier das erste Beispiel eines plastisch flexiblen 1D‐Koordinationspolymers vor. Die Verbindung [Zn(μ‐Cl)2(3,5‐Cl2Py)2]n ist über zwei kristallographische Flächen flexibel und bleibt bemerkenswerterweise auch bei 180° Biegung als Einkristall intakt. Mittels einer Kombination von Mikroskopie‐, Beugungs‐ und spektroskopischen Methoden untersuchen wir die strukturelle Reaktion des Kristallgitters auf mechanische Verformung. Laut den Ergebnissen scheint nicht die Deformation der kovalenten Polymerketten für die beobachtete makroskopische Biegung verantwortlich, sondern eine Verschiebung der Koordinationspolymerketten. Basierend auf experimentellen und theoretischen Erkenntnissen schlagen wir ein neues Modell für die mechanische Flexibilität von 1D‐Koordinationspolymeren vor. Darüber hinaus liefern unsere Berechnungen eine Ursache für die unterschiedlichen mechanischen Eigenschaften dieser Verbindung und eines strukturell ähnlichen elastisches Materials. [ABSTRACT FROM AUTHOR]

Mechanical flexibility in single crystals of covalently bound materials is a fascinating and poorly understood phenomenon. We present here the first example of a plastically flexible one‐dimensional (1D) coordination polymer. The compound [Zn(μ‐Cl)2(3,5‐dichloropyridine)2]n is flexible over two crystallographic faces. Remarkably, the single crystal remains intact when bent to 180°. A combination of microscopy, diffraction, and spectroscopic studies have been used to probe the structural response of the crystal lattice to mechanical bending. Deformation of the covalent polymer chains does not appear to be responsible for the observed macroscopic bending. Instead, our results suggest that mechanical bending occurs by displacement of the coordination polymer chains. Based on experimental and theoretical evidence, we propose a new model for mechanical flexibility in 1D coordination polymers. Moreover, our calculations propose a cause of the different mechanical properties of this compound and a structurally similar elastic material. [ABSTRACT FROM AUTHOR]

A pair of supramolecular isomers of CdII‐based MOF have been synthesized by utilizing a flexible N,N′‐donor linker and a dicarboxylate with ESIPT (excited‐state intramolecular proton transfer) fluorophore by varying the reaction media. One of the MOFs has a 3D four‐fold interpenetrating framework with guest solvent in the structure that undergoes a solvent‐dependent crystalline‐to‐crystalline structural transformation, which has been extensively studied by powder XRD and IR spectroscopy. The other MOF is structurally rigid in nature and has a two‐fold interpenetrating structure without any guest molecules. Both the compounds show moderate CO2 adsorption and one of them, the MOF with the four‐fold interpenetrating structure, also shows moderately high H2 adsorption. Furthermore, both the compounds show interesting luminescence behavior. In the solid state, the two compounds show single‐peak spectra, whereas upon suspension of these compounds in polar solvents, the maxima split into two peaks with a large Stokes shift. On the other hand, in nonpolar solvents, only one emission maximum is observed. This solvatochromic dual‐emission phenomenon is due to ESIPT, which has been extensively studied. [ABSTRACT FROM AUTHOR]

A guest-dependent dynamic fivefold interpenetrated 3D porous metal-organic framework (MOF) of ZnII ions has been synthesized that exhibits selective carbon dioxide adsorption. Furthermore, the MOF shows excellent luminescence behavior, which is supported by a systematic study on the guest-responsive multicolor emission of a suspension of the MOF. The dual-emission behavior arises from the excited-state intramolecular proton transfer (ESIPT), and the compound also shows remarkable potential to detect traces of water in various organic solvents. The experimental observations were also painstakingly authenticated by using time-dependent density-functional-theory (DFT) calculations. [ABSTRACT FROM AUTHOR]

A guest dependent dynamic framework of Zn(II) that shows excellent guest‐responsive multicolor emission behavior has been synthesized. The results are supported by time dependent density functional calculations. It has been found that the nice dual emission behavior of the system arises from the intramolecular proton transfer and that it helps to detect trace amounts of water in various organic solvents. More information can be found in the Full Paper by D. Ghoshal, S. Chakrabarti et al. on page 14998 ff. [ABSTRACT FROM AUTHOR]