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The halogen bonding involving the Au(i) metal center was systematically studied using a series of nine co-crystals between NHC Au(i) aryl complexes and iodoperfluoroarenes through XRD and solid-state NMR techniques, as well as DFT calculations.

One-dimensional cationic coordination polymers have been a promising platform for designing solid-state physical properties through diverse coordination geometries. In particular, the folding mode of the coordination polymers that form a helical structure directly determines the metal-centered coordination environment. Herein, we report N-heterocyclic carbene (NHC) Cu(I) cationic coordination polymers with pyrazine as the linker, which construct a 4-fold or 3-fold helical column in luminescent crystals using octahedral anions (SbF6- and PF6-) or a tetrahedral anion (BF4-), respectively. Single-crystal XRD studies revealed that the folding modes depend on the structural shape of the counteranions, which form H-F interactions between ligands and anions. Indeed, the folding mode change from 4-fold to 3-fold by including a different shape of the counteranions, resulting in red-shifted emission from approximately 580 to 687 nm, which is difficult to modulate in the solid state.

A series of mechanophores were studied computationally by employing the AFIR (Artificial Force Induced Reaction) method, which applies an artificial force on the molecule to trigger reactions, and meanwhile with a tensile force to simulate a mechanochemical reaction. The calculation results were both qualitatively and quantitatively consistent to those reported experimentally, indicating that the AFIR is a reliable approach to studying mechanochemical reactions. It was then applied to the study of retro-Diels-Alder reactions for the theoretical predictions of activation force levels which are currently unavailable. Moreover, it also helped to reveal the favored geometry for the enhancement of force effect. Later, the AFIR method was employed to study the mechanodegradation of generic polymers. The substituents effect and the polymer tacticity in strengthening the mechanical responsiveness, were highlighted by our study. Given the importance of cross-linker molecules in the double-network (DN) hydrogels, a fully automatic search of mechanochemical transformation pathways of a commonly used cross-linker molecule, N,N'-methylenebisacrylamide (MBAA), was also performed by the AFIR method. Through the work described in this article, we demonstrated that, in the field of polymer mechanochemistry, the AFIR method utilizing two forces is a simple but effective tool to give accurate predictions of activation force levels at any given timescale. In the meantime, the mechanistic study of mechanochemical reactions shown in this article is believed to provide insightful suggestions for the further design and application of mechanophores.

Among the known types of non-covalent interactions with Au(I) metal center, Au(I) involving halogen bonding (XB) remains a rare phenomenon that has not been studied systematically. Herein, using five N-heterocyclic carbene (NHC) Au(I) aryl complexes and two iodoperfluoroarenes as XB donors, we demonstrated that the XB involving the Au(I) metal center can be predictably obtained for neutral Au(I) complexes using the example of nine co-crystals. The presence of XBs involving the Au(I) center was experimentally investigated by single-crystal X-ray diffraction and solid-state 13C CP-MAS NMR methods, and their nature was elucidated through DFT calculations, followed by electron density, electrostatic potential, and orbital analyses. The obtained results revealed the connection between the structure of Au(I) complexes as XB acceptors and the geometrical, electronic, and spectroscopic features of XB interactions, as well as the supramolecular structure of the co-crystals

Herein, we report a novel strategy for introducing a luminophore into generic polymers facilitated by mechanical stimulation. In this study, polymeric mechanoradicals were formed in situ under ball-milling conditions to undergo radical-radical coupling with a prefluorescent nitroxide-based reagent in order to incorporate a luminophore into the polymer main chains via a covalent bond. This method allowed the direct and conceptually simple preparation of luminescent polymeric materials from a wide range of generic polymers such as polystyrene, polymethyl methacrylate, and polyethylene. These results indicate that the present mechanoradical coupling strategy may help to transform existing commodity polymers into more valuable functional materials.

Charge-transfer (CT) crystals bearing segregated domains between the electron donor and acceptor molecules are a promising platform for developing new organic functional solid-state materials. However, there is limited diversity in the segregated structures of CT crystals. Herein, we report a novel structure of a CT crystal using hexaarylbenzene (HAB) and tetracyanoquinodimethane (TCNQ) as the electron donors and acceptors, respectively. Single-crystal X-ray diffraction (XRD) studies revealed that hexapyridylbenzene and TCNQ form a segregated layer in crystalline media, and the CT feature of TCNQ was observed in terms of the observed chemical bond lengths in the crystal.

Herein we report a crystalline molecular rotor with rotationally modulated triplet emission that displays macroscopic dynamics in the form of crystal moving and/or jumping, also known as salient effects. Molecular rotor 2 with a central 1,4-diethynyl-2,3-difluorophenylene rotator linked to two gold(I) nodes, crystalizes as infinite 1D chains through intermolecular gold(I)-gold(I) interactions. The rotational motion changes the orientation of the central phenylene, changing the electronic communication between adjacent chromophores, and thus the emission intensities. Crystals of 2 showed the large and reversible thermal expansion/compression anisotropy, which accounts for 1) a nonlinear Arrhenius behavior in molecular-level rotational dynamics, which correlates with 2) changes in emission, and determines 3) the macroscopic crystal motion. A molecular rotor analogue 3 has properties similar to those of 2, suggesting a generalized way to control mechanical properties at molecular and macroscopic scales.

Molecular spur gear dynamics with high gearing fidelity can be achieved through a careful selection of constituent molecular components that favorably position and maintain the two gears in a meshed configuration. Here, we report the synthesis of a new macrocyclic molecular spur gear with a bibenzimidazole stator combined with a second naphthyl bis-gold-phosphine gold complex stator to place two 3-fold symmetric 9,10-diethynyl triptycene cogs at the optimal distance of 8.1 A for gearing. Micro electron diffraction (μED) analysis confirmed the formation of the macrocyclic structure and the proper alignment of the triptycene cogs. Gearing dynamics in solution are predicted to be extremely fast and, in fact, were too fast to be observed with variable-temperature 1H NMR using CD2Cl2 as the solvent. A combination of molecular dynamics and metadynamics simulations predict that the barriers for gearing and slippage are ca. 4 kcal mol-1 and ca. 9 kcal mol-1, respectively. This system is characterized by enhanced gearing fidelity compared to the acyclic analog. This is achieved by rigidification of the structure, locking the two triptycenes in the preferred gearing distance and orientation.

In crystalline solids, molecules generally have limited mobility due to their densely packed environment. However, structural information at the molecular level may be used to design amphidynamic crystals with rotating elements linked to rigid, lattice-forming parts, which may lead to molecular rotary motions and changes in conformation that determine the physical properties of the solid-state materials. Here, we report a novel design of emissive crystalline molecular rotors with a central pyrazine rotator connected by implanted transition metals (Cu or Au) to a readily accessible enclosure formed by two

Herein, a novel mechano-responsive luminescent (MRL) material based on crystal-to-crystal phase transitions between crystals of a chiral and those of a centrosymmetric space group, accompanied by a change of emission properties, is described. Initially, a gold complex containing a biphenyl moiety, which exhibits an achiral structure in solution, afforded an orange-emitting amorphous phase together with a viscous isotropic oil after evaporation of the solvent. Upon pricking, the orange-emitting oil spontaneously crystallized either in a centrosymmetric or in a chiral space group while simultaneously changing the emission properties. Remarkably, grinding the chiral crystals induced a solid-state phase transition to the achiral crystals under concomitant changes of the emission properties.

A new method was developed for the first catalytic enantioselective borylation of aliphatic ketones. A variety of substrates reacted efficiently with bis(pinacolato)diboron in the presence of a copper(I)/chiral N-heterocyclic carbene complex catalyst to furnish optically active tertiary α-hydroxyboronates with moderate to high enantioselectivities (up to 94 % ee). Notably, the product could be converted into the chiral tertiary alcohol derivative using a stereospecific boron functionalization process. The theoretical study of the mechanism for the enantioselectivity is also described.

Luminescent crystalline materials that are sensitive to volatile organic solvents are useful for detection of harmful gases. Although such compounds have been reported, discrimination of various types of volatile organic compounds using one compound remains challenging. Here, it is described that introduction of a biphenyl unit into a gold isocyanide scaffold (denoted complex 3) enables discrimination of various volatile organic compounds by forming 11 solvent-containing crystal structures 3/solvent with different emission properties (emission maxima of 490–580 nm). Mechanical stimulation of 3/solvent affords amorphous 3ground without solvent inclusion. The resulting 3ground can again detect volatile compounds by forming 3/solvent with concomitant emission color changes. A dozen single crystals of 3, which include 11 solvated 3/solvent and one solvent-free 3/none, also are represented. Comparison of various crystallographic parameters of 3/solvent and 3/none with their corresponding optical properties indicates that a combination of various structural properties of 3 affects the optical properties of 3. This study reveals that the introduction of a biphenyl moiety could be a useful design to develop versatile indicators for solvents through the formation of multiple luminescent crystal structure.

Here a structural design aimed at the control of phosphorescence emission as the result of changes in molecular rotation in a crystalline material is presented. The proposed strategy includes the use of aurophilic interactions, both as a crystal engineering tool and as a sensitive emission probe, and the use of a dumbbell-shaped architecture intended to create a low packing density region that permits the rotation of a central phenylene.

Luminescent compounds that are sensitive to volatile organic solvents are useful for detection of harmful gases. Although such compounds have been reported, discrimination of various types of volatile organic compounds using one compound remains challenging. We reported a series of gold isocyanide complexes that form various crystalline structures with distinct emission properties, which can be interconverted by mechanical stimulation and solvent addition. Here, we report that introduction of a biphenyl unit into a gold isocyanide scaffold (denoted complex 3) enables discrimination of various volatile organic compounds by forming 11 solvent-containing crystal structures 3/solvent [solvent can be CHCl3, pyridine (Py), CH2Cl2, CH2Br2, dimethylacetamide (DMA), acetaldehyde (AcH), CH3CN, DMF, (S)-propylene oxide (SPO), rac-propylene oxide (racPO), or acetone] with different emission properties (emission maxima of 490–580 nm). Mechanical stimulation of 3/solvent affords amorphous 3ground without solvent inclus...

Density functional theory calculations were performed to validate the proposed reaction mechanism for the enantioselective nucleophilic borylation of a polarized C═O double bond in the presence of diphosphine/borylcopper(I) complexes. Consequently, we successfully elucidated the origin for the regioselectivity and the mechanism for the enantioselectivity of the reaction. We also obtained theoretical explanations for the fact that the presence of a proton source gave a higher reactivity and a better enantioselectivity in the borylation reaction of aldehydes with a copper(I)/(R)-DTBM-SEGPHOS complex catalyst. This study is particularly valuable toward the development and design of novel enantioselective borylation reactions with polarized carbon–heteroatom double bonds.

Luminescent mechanochromism of a chiral gold(i) complex is investigated. The racemic and homochiral forms of the gold(i) complex possess distinct crystal packing arrangements with different emission colors. Upon mechanical stimulation, both crystals transform into amorphous powders that exhibit similar emission colors.

Luminescence alterations in solid-state materials upon external stimulations have attracted much attention due to their potential for the development of highly functional devices or sensors. We have previously reported the first examples of mechano-induced single-crystal-to-single-crystal (SCSC) phase transitions of gold(I) isocyanide complexes under concomitant emission-color changes. However, the reverse phase transitions of the crystals obtained after mechanical stimulation have not yet been achieved. Herein, a reversible change of the luminescence based on two SCSC phase transitions via mechanical cutting and solvent-vapor adsorption is described. Crystallization of a gold(I) complex that bears CF3 and biaryl moieties from CH2Cl2/MeOH afforded a green-emitting single crystal packed in a polar space group (Pna21). The green-emitting single crystals included MeOH molecules. Upon cutting the crystal under MeOH vapor at 22 °C, the green-emitting single crystal spontaneously changed into a centrosymmetric ...

Here we present a structural design aimed at the control of phosphorescence emission as the result of changes in molecular rotation in a crystalline material. The proposed strategy includes the use of aurophilic interactions, both as a crystal engineering tool and as a sensitive emission probe, and the use of a dumbbell-shaped architecture intended to create a low packing density region that permits the rotation of a central phenylene. Molecular rotor 1, with a central 1,4-diethynylphenylene rotator linked to two gold(I) triphenylphosphane complexes, was prepared and its structure confirmed by single-crystal X-ray diffraction, which revealed chains mediated by dimeric aurophilic interactions. We showed that green-emitting crystals exhibit reversible luminescent color changes between 298 and 193 K, which correlate with changes in rotational motion determined by variable-temperature solid-state 2H NMR spin–echo experiments. Fast two-fold rotation with a frequency of ca. 4.00 MHz (τ = 0.25 μs) at 298 K becom...

Isocyanates with oligo(ethylene glycol) units have been designed and synthesized as 2,5-dioxaheptyl, 2,5,8-trioxadecyl, 3,6,9-trioxaundecyl, and 2,5,8,11-tetraoxatridecyl isocyanates (MeEO2IC, MeEO3IC, EtEO3IC, and MeEO4IC, respectively). The bulk polymerization of the isocyanates using n-butoxy(η5-cyclopentadienyl)dichlorotitanium(IV) at 10 °C proceeded via a living manner to produce well-defined water-soluble polyisocyanates of PMeEO3IC, PEtEO3IC, and PMeEO4IC except for PMeEO2IC. The phase transition property of the obtained polyisocyanates was estimated by their cloud point temperatures (Tcps) in an aqueous solution (40 g L−1). For PMeEO3IC, the Tcp decreased from 90.0 to 74.9 °C with the increasing molecular weight (Mn,NMR) from 1960 to 9000 g mol−1. The Tcp of 94.0 °C for PMeEO4IC (4460 g mol−1) was higher than that of 79.6 °C for PMeEO3IC (4560 g mol−1), and the Tcp decreased from 79.6 to 34.7 °C by changing from the methyl to the ethyl group in the oligo(ethylene glycol) units from PMeEO3IC to PEtEO3IC (4470 g mol−1).