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We report here a new green fluorescent organic crystal of an amide functionalized acrylonitrile derivative (E-ArF2) that displays various types of macroscopic response when illuminated with UV light (390 nm). The shape deformation and actuation of the E-ArF2 crystal can be controlled on-demand by shining UV-light on the specific parts of the crystal and reversing the direction of light illumination. When UV light is shone on the (001) face of a straight crystal, it rapidly bends away from the light source and can be bent to the opposite direction by reversing the illumination direction on the other face (00−1). With the aid of various analytical techniques, NMR, IR, UV-vis and X-ray diffraction, we established that the light fueled macroscopic actuation of the E-ArF2 crystal is rooted to the combined effect of E- to Z-isomerization and the [2 + 2] cycloaddition reaction in the solid state. Based on the above experimental facts, a general mechanistic model of the actuation is also proposed.

Amines are ubiquitous in biological world, but are toxic and harmful in nature. Detection of biogenic amines that are released from spoiled seafood, meat, or dairy products is an important task to maintain the quality and safety of these packaged foods. To this endeavor, herein we report pyrylium salts that are capable of sensing various amines by rapid change of fluorescence color or intensity. In molecular level, this change of fluorescence is rooted to the formation of pyridine or analogous product that have distinct optical property. The pyrylium salts are capable of efficiently sensing amine vapors or amine solutions both in solid state and in solution state and thus demonstrating a multiphase sensing platform. Utilizing the excellent sensing property, we have employed our pyrylium compounds as spoilage indicator for food products such as fish, meat or cheese which relies on sensing biogenic amines released from these spoiled foods and provide optical response. Prominent change in visible and luminescence color was observed within 4-18 h of packaging at room temperature (∼33 °C). Considering the rapid response for biogenic amines, these molecular sensors have great potential to be utilized for food packaging industry, medical diagnostics, or other sensory devices.

In this study, we report a synthetically simple donor-acceptor (D-A)-type organic solid-state emitter 1 that displays unique fluorescence switching under mechanical stimuli. Orange and yellow emissive crystals of 1 (1O, 1Y) exhibit an unusual "back and forth" fluorescence response to mechanical force. Gentle crushing (mild pressure) of the orange or yellow emissive crystal results in hypsochromic shift to cyan emissive fragments (lambda(em) = 498-501 nm) with a large wavelength shift Delta lambda(em) = -71 to -96 nm, while further grinding results in bathochromic swing to green emissive powder lambda(em) = 540-550 nm, Delta lambda(em) = + 40 to 58 nm. Single-crystal X-ray diffraction study reveals that molecules are packed by weak interactions, such as C-H center dot center dot center dot pi, C-H center dot center dot center dot N, and C-H center dot center dot center dot F, which facilitate intermolecular charge transfer in the crystal. With the aid of structural, spectroscopic, and morphological studies, we established the interplay between intermolecular and intramolecular charge-transfer interaction that is responsible for this elusive mechanochromic luminescence. Moreover, we have also demonstrated the application of this organic material for chlorine gas sensing in solid state.

In this study, we report the preparation of two novel zinc-porphyrin derivatives (ZnP-3DoH-click-CNCOOH and ZnP-3DoH-click-COOH) and two reference compounds (ZnP-3DoH-CNCOOH and ZnP-3DoH-COOH) as sensitizers in dye-sensitized solar cells (DSCs). The photo-physical and electrochemical measurements along with the computational studies suggest that the four synthesized porphyrin derivatives exhibit appropriate light absorption characteristics as well as suitable molecular orbital levels for their use as sensitizers in DSCs. All the modified zinc-porphyrin complexes bear hexyloxy chains at the ortho-positions of their three phenyl rings and contain either a carboxylic or a cyanoacrylic acid as anchoring group. In the zinc-porphyrin derivatives ZnP-3DoH-click-CNCOOH and ZnP-3DoH-click-COOH, a spacer with an electron withdrawing unit was incorporated between the porphyrin ring and each anchoring group. More specifically, the triazole ring was used as a spacer since it is considered to be a highly efficient electron transfer bridge. In addition, the pentafluoro-phenyl ring was selected due to its strong electron withdrawing ability in both final derivatives (ZnP-3DoH-click-CNCOOH and ZnP-3DoH-click-COOH). Following this strategy, fourfold and eightfold increase of the device performance was observed regarding ZnP-3DoH-click-CNCOOH and ZnP-3DoH-click-COOH, respectively, when compared to the efficiencies achieved with the reference compounds (ZnP-3DoH-COOH and ZnP-3DoH-CNCOOH). A more detailed interpretation of the charge dynamics in these devices was carried out using charge extraction (CE) and open-circuit voltage decay (OCVD) measurements.

In this study, we report the first example of polymorphic Sn(IV)-tetrapyridyl porphyrins axially armed with halogen (Cl, Br)-substituted carboxyphenyl ligands (structural formula [Sn(tPyP)2+(A−)2], where A is the axial ligand = 3,5-dichloro/dibromo benzoic acid). The two polymorphs of chloro-substituted Sn(IV)-tetrapyridyl porphyrin (1α and 1β) display distinct photophysical and morphological properties in the solid state. X-ray diffraction study reveals that these polymorphs 1α and 1β greatly differ in supramolecular architecture and noncovalent interactions, which is responsible for their distinct solid-state properties. Molecules of the two polymorphs adopt different conformations of the axial carboxyphenyl ligand. Crystal packing of these polymorphs are dominated by intermolecular C–H···Npyridine, C–H···O, C–H···π, and Cl···Npyridin interactions. Theoretical study showed that the energy difference between the two polymorphs is ∼8 kcal/mol. In addition to these polymorphs, a reference compound 2 with a...

Plastic bending of organic crystals is a well-known, yet mechanistically poorly understood phenomenon. On three structurally related epimers, derivatives of galactose, glucose, and mannose, it is demonstrated here that small changes in the molecular structure can have a profound effect on the mechanical properties. While the galactose derivative affords crystals which can be easily bent, the crystals of the derivatives of glucose and mannose are brittle and do not bend. Structural, microscopic, and mechanical evidence is provided showing that hydrogen bonding of water molecules is the key element for sliding over the slip planes in the crystal and accounts for the plastic bending.

The range of unit cell orientations generated at the kink of a bent single crystal poses unsurmountable challenges with diffraction analysis and limits the insight into the molecular-scale mechanism of bending. On a plastically bent crystal of hexachlorobenzene, it is demonstrated here that spatially resolved microfocus infrared spectroscopy using synchrotron radiation can be applied in conjunction with periodic density functional theory calculations to predict spectral changes or to extract information on structural changes that occur as a consequence of bending. The approach reproduces well the observed trends, such as the wall effects, and provides estimations of the vibrational shifts, unit cell deformations, and intramolecular parameters. Generally, expansion of the lattice induces red-shift while compression induces larger blue-shift of the characteristic ν(C–C) and ν(C–Cl) modes. Uniform or non-uniform expansion or contraction of the unit cell of 0.1 A results in shifts of several cm–1, whereas def...

When exposed to external stimuli such as heat or light, certain single crystals can acquire momentum and undergo motion. On a molecular scale, the motility of such dynamic single crystals is triggered by a phase transition or chemical reaction without gaseous products, and macroscopically manifests as either slow (reversible or irreversible) deformation, or as rapid, almost instantaneous propulsion of the crystals that is oftentimes accompanied by disintegration. While the elastic energy of the slow reconfiguration processes such as bending, twisting and coiling can be utilized for actuation of other objects, the fast disintegrative processes could be exploited to initiate pressure-sensitive applications. This short review intends to summarize recent developments in the growing research on dynamic crystals, especially aspects of the mechanism of rapid motion of thermosalient and photosalient (leaping) crystals. The collective evidence indicates that these solids are organic-based analogues of the inorganic martensitic materials. While qualitative explanation of the molecular processes that lead to the related dynamic phenomena can be provided, quantification of their kinematics, estimation of the useful work that can be extracted, and prediction of their occurrence are yet to be established. Harnessing the potential of these materials to rapidly and efficiently perform the fundamentally important process of transduction of heat or light into kinetic energy appears as a prospective basis for their application in motion gears and devices.

In this study, we report a deep red emissive organic crystal that displays high contrast fluorescence switching under mechanical and thermal stimulation. Upon mechanical grinding, the pristine red emissive crystals of 1R (λem = 667 nm) transformed into green emissive crystalline powder (λem = 550 nm) with a remarkable hypsochromic shift of wavelength, Δλ = 117 nm. The melting of 1R leads to a green emissive amorphous solid (λem = 555 nm) with a wavelength shift of Δλ = 112 nm. Upon fuming with different solvents, the amorphous melt solid transforms into different polymorphs having distinct emission characters. The structural relationship between different emissive states is investigated with the aid of X-ray diffraction and other spectroscopic studies, which clearly demonstrate the roles of ordered molecular packing and intermolecular interaction in determining their diverse optical response.

Angewandte Chemie / International edition 56(28), 8104 - 8109 (2017). doi:10.1002/anie.201702359, In salient effects, still crystals of solids that switch between phases acquire a momentum and are autonomously propelled because of rapid release of elastic energy accrued during a latent structural transition induced by heat, light, or mechanical stimulation. When mechanical reconfiguration is induced by change of temperature in thermosalient crystals, bursts of detectable acoustic waves are generated prior to self-actuation. These observations provide compelling evidence that the thermosalient transitions in organic and organic-containing crystals are molecular analogues of the martensitic transitions in some metals, and metal alloys such as steel and shape-memory alloys. Within a broader context, these results reveal that, akin to metallic bonding, the intermolecular interactions in molecular solids are capable of gradual accrual and sudden release of a substantial amount of strain during anisotropic thermal expansion, followed by a rapid transformation of the crystal packing in a diffusionless, non-displacive transition., Published by Wiley, Weinheim

Six mononuclear Ir complexes (1–6) using polypyridyl-pyrazine based ligands (L1 and L2) and {[cp*IrCl(μ-Cl)]2 and [(ppy)2Ir(μ-Cl)]2} precursors have been synthesised and characterised. Complexes 1–5 have shown potent anticancer activity against various human cancer cell lines (MCF-7, LNCap, Ishikawa, DU145, PC3 and SKOV3) while complex 6 is found to be inactive. Flow cytometry studies have established that cellular accumulation of the complexes lies in the order 2 > 1 > 5 > 4 > 3 > 6 which is in accordance with their observed cytotoxicity. No changes in the expression of the proteins like PARP, caspase 9 and beclin-1, Atg12 discard apoptosis and autophagy, respectively. Overexpression of CHOP, activation of MAPKs (P38, JNK, and ERK) and massive cytoplasmic vacuolisation collectively suggest a paraptotic mode of cell death induced by proteasomal dysfunction as well as endoplasmic reticulum and mitochondrial stress. An intimate relationship between p53, ROS production and extent of cell death has also been established using p53 wild, null and mutant type cancer cells.

The ability of thermosalient solids, organic analogues of inorganic martensites, to move by rapid mechanical reconfiguration or ballistic event remains visually appealing and potentially useful, yet mechanistically elusive phenomenon. Here, with a material that undergoes both thermosalient and non-thermosalient phase transitions, we demonstrate that the thermosalient effect is preceded by anomalous thermal expansion of the unit cell. The crystal explosion occurs as sudden release of the latent strain accumulated during the anisotropic, exceedingly strong expansion of the unit cell with αa = 225.9 × 10−6 K−1, αb = 238.8 × 10−6 K−1 and αc = −290.0 × 10−6 K−1, the latter being the largest negative thermal expansivity observed for an organic compound thus far. The results point out to the occurence of the thermosalient effect in phase transitions as means to identify new molecular materials with strong positive and/or negative thermal expansion which prior to this work could only be discovered serendipitously.

Artificial light-harvesting systems have until now not been able to self-assemble into structures with a large photon capture cross-section that upon a stimulus reversibly can switch into an inactive state. Here we describe a simple and robust FLFL-dipeptide construct to which a meso-tetraphenylporphyrin has been appended and which self-assembles to fibrils, platelets or nanospheres depending on the solvent composition. The fibrils, functioning as quenched antennas, give intense excitonic couplets in the electronic circular dichroism spectra which are mirror imaged if the unnatural FDFD-analogue is used. By slightly increasing the solvent polarity, these light-harvesting fibres disassemble to spherical structures with silent electronic circular dichroism spectra but which fluoresce. Upon further dilution with the nonpolar solvent, the intense Cotton effects are recovered, thus proving a reversible switching. A single crystal X-ray structure shows a head-to-head arrangement of porphyrins that explains both their excitonic coupling and quenched fluorescence., Artificial light-harvesting systems cannot self-assemble into photon-capturing structures that can reversibly switch into an inactive state. Here, the authors describe a simple and robust dipeptide construct which self-assembles to fibrils, platelets or nanospheres with varying optical properties.

When heated, single crystals of enantiomerically pure D- and L-pyroglutamic acid (PGA) are capable of recurring self-actuation due to rapid release of latent strain during a structural phase transition, while the racemate is mechanically inactive. Contrary to other thermosalient materials, where the effect is accompanied by crystal explosion due to ejection of debris or splintering, the chiral PGA crystals respond to internal strain with unprecedented robustness and can be actuated repeatedly without deterioration. It is demonstrated that this superelasticity is attained due to the low-dimensional hydrogen-bonding network which effectively accrues internal strain to elicit propulsion solely by elastic deformation without disintegration. One of the two polymorphs (β) associated with the thermosalient phase transition undergoes biaxial negative thermal expansion (αa = -54.8(8) × 10(-6) K(-1), αc = -3.62(8) × 10(-6) K(-1)) and exceptionally large uniaxial thermal expansion (αb = 303(1) × 10(-6) K(-1)). This second example of a thermosalient solid with anomalous expansion indicates that the thermosalient effect can be expected for first-order phase transitions in soft crystals devoid of an extended 3D hydrogen-bonding network that undergo strongly anisotropic thermal expansion around the phase transition.