Spontaneous Symmetry Breaking of Achiral Molecules Leading to the Formation of Homochiral Superstructures that Exhibit Mechanoluminescence.

Chirality, with its intrinsic symmetry-breaking feature, is frequently utilized in the creation of acentric crystalline functional materials that exhibit intriguing optoelectronic properties. On the other hand, the development of chiral crystals from achiral molecules offers a solution that bypasses the need for enantiopure motifs, presenting a promising alternative and thereby expanding the possibilities of the self-assembly toolkit. Nevertheless, the rational design of achiral molecules that prefer spontaneous symmetry breaking during crystallization has so far been obscure. In this study, we present a series of six achiral molecules, demonstrating that when these conformationally flexible molecules adopt a cis-conformation and engage in multiple non-covalent interactions along a helical path, they collectively self-assemble into chiral superstructures consisting of single-handed supramolecular columns. When these homochiral supramolecular columns align in parallel, they form polar crystals that exhibit intense luminescence upon grinding or scraping. We therefore demonstrate our molecular design strategy could significantly increase the likelihood of symmetry breaking in achiral molecular synthons during self-assembly, offering a facile access to novel chiral crystalline materials with unique optoelectronic properties.

Halogen Bonding Adsorbent Pyridine N-oxides for Iodine Capture in Water.

Rapid capture of 129 I with high volatility and toxicity in the environment has attracted much attention. Herein we reported a firstly synthesized nonporous material: pyridine N-oxides (NTPO and ATPO) as iodine adsorbent. Both of NTPO and ATPO exhibit remarkable performance on the adsorption of iodine in aqueous solution, vapor state and organic solvents. Upon the capture of iodine, pyridine N-oxides were transformed to binary cocrystals combined with the pyridine N-oxides and iodine which is driven by halogen bond between iodine and oxygen atoms. Moreover, pyridine N-oxides shows high chemical, thermal and moisture stability.

The Effect of Electron Donation and Intermolecular Interactions on Ultralong Phosphorescence Lifetime of 4-Carnoyl Phenylboronic Acids.

Purely organic phosphors with persistent room-temperature phosphorescence (RTP) demonstrate promising potential applications in optoelectronic area, bioimaging, and chemical sensing. However, it is still a formidable challenge to further design new organic phosphors due to the unclear mechanism to produce ultralong phosphorescence lifetimes. This paper investigates the correlation between the ultralong phosphorescence lifetime and structure of a series of 4-carbonylphenylboronic acid derivatives in the crystal state. Experimental and calculation results reveal that the electron-donating effect of substituents makes the phosphorescence lifetime longer by not only weakening the vibration relaxation of the excited triplet state but also increasing the energy of T1. Moreover, numerous intermolecular interactions for reducing nonradiative relaxation and the degree of the π-π stacking for stabilizing the triplet state are beneficial to the persistent RTP. The work is conducted to clarify the structure-property correlation of phosphorescent materials and design new persistent phosphors. Finally, an attempt is completed using phosphorescent materials to design two-dimensional or three-dimensional codes and anticounterfeiting applications.

σ-Hole Bond vs π-Hole Bond: A Comparison Based on Halogen Bond.

The σ-hole and π-hole are the regions with positive surface electrostatic potential on the molecule entity; the former specifically refers to the positive region of a molecular entity along extension of the Y-Ge/P/Se/X covalent σ-bond (Y = electron-rich group; Ge/P/Se/X = Groups IV-VII), while the latter refers to the positive region in the direction perpendicular to the σ-framework of the molecular entity. The directional noncovalent interactions between the σ-hole or π-hole and the negative or electron-rich sites are named σ-hole bond or π-hole bond, respectively. The contributions from electrostatic, charge transfer, and other terms or Coulombic interaction to the σ-hole bond and π-hole bond were reviewed first followed by a brief discussion on the interplay between the σ-hole bond and the π-hole bond as well as application of the two types of noncovalent interactions in the field of anion recognition. It is expected that this review could stimulate further development of the σ-hole bond and π-hole bond in theoretical exploration and practical application in the future.

Halogen bonding in the design of organic phosphors.

Halogen bonding as a new strategy for introducing heavy atom perturbers in defined stoichiometry in the design of organic phosphors is reviewed. Considering ten novel cocrystals assembled by polyaromatic hydrocarbons (PAHs) and their heterocyclic analogues and haloperfluorobenzenes using the new strategy, apart from biphenyl cocrystals they all phosphoresce strongly, showing that the new methodology can induce phosphorescence by a heavy atom effect. More interesting, the phosphorescence properties, including excitation/emission wavelengths and decay dynamics, show dependence on the structure of the PAHs and interaction patterns, which is very important and valuable in modulation of the expected colors of luminescent materials.

Strength order and nature of the π-hole bond of cyanuric chloride and 1,3,5-triazine with halide.

The (13)C NMR chemical shift moving upfield indicates the main model of π-holeX(-) bond between cyanuric chloride/1,3,5-triazine (3ClN/3N), which possess both the π-hole and σ-hole, and X(-). (13)C NMR and UV absorption titration in acetonitrile confirmed that the bonding abilities of 3ClN/3N with X(-) follow the order I(-) > Br(-) > Cl(-), which is apparently the order of the charge transfer ability of halide to 3ClN/3N. Chemical calculations showed that the bonding abilities in solution were essentially consistent with those obtained by titration experiments. However, the results in the gas phase were the reverse, i.e., π-holeCl(-) > π-holeBr(-) > π-holeI(-) in bonding energy, which obeys the order of electrostatic interaction. In fact, the π-hole bond and σ-hole bond compete with solvation and possible anion-hydrogen bond between a solvent molecule and a halide in solution. An explanation is that the apparent charge transfer order of π-/σ-holeI(-) > π-/σ-holeBr(-) > π-/σ-holeCl(-) occurs for weak π-hole bonds and σ-hole bonds, whereas the order of electrostatic attraction of π-/σ-holeCl(-) > π-/σ-holeBr(-) > π-/σ-holeI(-) is valid for strong bonds. It can be concluded by combining energy decomposition analysis and natural bond orbital analysis that the π-holeX(-) bond and σ-holeX(-) bond are electrostatically attractive in nature regardless of whether the order is I(-) > Br(-) > Cl(-) or the reverse.

Synthesis of a novel fluorescent probe based on 7-nitrobenzo-2-oxa-1,3-diazole skeleton for the rapid determination of vitamin B12 in pharmaceuticals.

A new fluorescent probe, 4-N,N-di(2-hydroxyethyl)imino-7-nitrobenzo-2-oxa-1,3-diazole (HINBD) was synthesized in a single step with reasonably good yield. The water-soluble HINBD emits strongly in the visible region (λex = 479 nm, λem = 545 nm) and is stable over a wide range of pH values. It was found that vitamin B12 (VB12 ) had the ability to quench the fluorescence of HINBD, and the quenched fluorescence intensity was proportional to the concentration of VB12 . A method for VB12 determination based on the quenching fluorescence of HINBD was thus established. Interference effects of various substances, including sugars, vitamins, amino acids, inorganic cations and some organic substances have been studied. Under optimal conditions, the linear range is 0.0-2.4 × 10(-5) mol/L. The determination limit is 8.3 × 10(-8) mol/L. The method was applied to measure VB12 in pharmaceutical preparations with satisfactory results.

The C-I···X¯ halogen bonding of tetraiodoethylene with halide anions in solution and cocrystals investigated by experiment and calculation.

The selection of the halogen bonding (XB) donor is an important factor in molecular recognition of halides by XB. Here XB complexes between tetraiodoethylene (TIE) as another donor instead of iodoperfluorobenzene and halides are investigated using UV-Vis, Raman, FT-IR, XRD, PXRD and calculations. A 1 : 1 stoichiometry of TIE with halide anions in dilute solution is confirmed. Comparatively, the TIECl(-) complex possesses greater bonding constant and molar extinction coefficient than TIEBr(-)/I(-), probably due to Cl(-) having the most negative electrostatic potential, or higher electronic density due to its small size. The XRD reveals that TIE/Cl(-) and TIE/I(-) cocrystals always keep the stoichiometry of 3 : 1 and 1 : 1, respectively, regardless of which solvent is used for preparing them. But the intermediate TIE/Br(-) cocrystals swing between 3 : 1 and 1 : 1. These results indicate that the TIEBr(-) complex should be influenced more easily by solvent nature and the stoichiometries of interaction between TIE and halide anions are different in solution and cocrystals. Moreover, the calculation of energies of XB interaction indicates that the XB strength of C-IX(-) is much stronger in the gas-phase and cocrystals than in solution, and much stronger than C-Iπ and C-II-C contacts in cocrystals. The study will be of benefit in anion recognition and new material design using XB.

Cocrystals assembled from iodoperfluorobenzene and flexible NTPO via halogen and π-hole bonds.

Two binary cocrystals of 1,4-diiodotetrafluorobenzene (1,4-DITFB, C6F4I2) and 1,3,5-trifluoro-2,4,6-triiodobenzene (1,3,5-TITFB, C6F3I3) with the flexible 2-{[(naphthalen-2-yl)methyl]sulfanyl}pyridine 1-oxide (NTPO, C16H13NOS) molecule were successfully prepared and characterized by X-ray diffraction and quantum chemistry calculation methods. X-ray diffraction analysis reveals that the conformation of the flexible NTPO molecule has been changed significantly after introducing the 1,4-DITFB or 1,3,5-TITFB molecule into the NTPO lattice. Also the formation of the binary cocrystals is driven mainly by robust C-I...-O-N+ halogen bonds and π-hole...π-bond interactions, and they possess `sandwich' structural frameworks. Moreover, interaction energy analysis and AIM analysis were used to explore the contribution of different fragments to the structural stability and the corresponding electronic properties, which reveals that the robust halogen bonds with shorter bonding lengths [2.768 (4) and 2.789 (3) Å] are suggested to be covalent to a certain degree.

Substance P conjugated to CdTe quantum dots triggers cytosolic calcium concentration oscillations and induces quantum dots internalization in the pancreatic carcinoma cell line AR4-2J.

Highly fluorescent CdTe quantum dots (QDs) stabilized by 3-mercaptopropionic acid were prepared by an aqueous solution approach and used as a fluorescent label to link substance P (SP) in studying the interaction of SP with NK-1 receptor, which was expressed on the AR4-2J cell line. Nonspecific adsorptions of CdTe QDs on the AR4-2J cell membrane were observed, whereas the QD-SP conjugates successfully crossed the cell membrane and entered the cytosol. SP is a neurotransmitter, and neurotransmitter-induced calcium concentration oscillation is a common phenomenon in diverse cells especially of secretory type. Cytosolic calcium concentration responses were studied in the AR4-2J cell line during stimulation with SP and QD-SP conjugates. The oscillations triggered by SP and QD-SP conjugates were dose-dependent and very similar. Such QD-SP conjugates readily internalized into the cytosol as would be expected of an active NK-1 ligand. Therefore QD-SP conjugates could be used successfully to study ligand and NK-1 receptor interactions in live cells. Our research may provide a meaningful reference for congener research.

Strong halogen bonding of 1,2-diiodoperfluoroethane and 1,6-diiodoperfluorohexane with halide anions revealed by UV-Vis, FT-IR, NMR spectroscopes and crystallography.

The spectroscopic methods UV-Vis absorption, FT-IR and (13)C and (19)F NMR demonstrate that 1,2-diiodoperfluoroethane (DIPFE) and 1,6-diiodoperfluorohexane (DIPFH) display strong halogen bonding with halide anions. A 1 : 1 stoichiometry of DIPFE or DIPFH with halide anion is confirmed, and the bonding constants and molar extinction coefficients are obtained. With the same halide, DIPFH possesses greater bonding constants and molar extinction coefficients than DIPFE. Furthermore, the bonding constants present in this article are far greater than those of all halogen bonding complexes reported. Interestingly, the FT-IR spectrum indicates that halogen bonding promotes a conversion from gauche to trans conformer of DIPFE. The X-ray data further confirm a 1 : 1 stoichiometry and all DIPFE and DIPFH exist in trans conformers in cocrystals which were assembled with halide anions. As potential persistent organic pollutions, iodinated perfluoroalkanes have been paid much attention. The present study will benefit current research of their separation and recognition in environmental samples.

Chemical and photophysical mechanism of fluorescence enhancement of 3-quinolineboronic acid upon change of pH and binding with carbohydrates.

The free 3-quinolineboronic acid (3-QBA) with the lowest (n-π*) excited singlet is non- or weakly fluorescent while protonated 3-QBA has the lowest (π-π*) excited singlet state and is highly fluorescent. The hybridization of boronic atom or charge transfer from aromatic ring to boronic acid group plays a secondary role in affecting fluorescence intensity. Binding with carbohydrate at a proper acidity, the hybridization of boron atom changes from sp(2) to sp(3) and the nitrogen atom in the quinoline ring is partially protonated, resulting in large enhancement of fluorescence. Meanwhile, the fluorescent lifetime of 3-QBA produces obvious change by binding with carbohydrates. Quinoline boronic acid is an important water-soluble fluorescence sensor for carbohydrate recognition. Both the remarkable changes in intensity and lifetime of 3-QBA can act as working parameters in recognition of carbohydrates at physiological pH.

Interaction of ß-cyclodextrin-capped CdSe quantum dots with inorganic anions and cations.

A facile method was developed for the preparation of water soluble ß-Cyclodextrin (ß-CD)-modified CdSe quantum dots (QDs) (ß-CD-QDs) by directly replacing the oleic acid ligands on the QDs surface with ß-CD in an alkaline aqueous solution. The as-prepared QDs show good stability in aqueous solution for several months. Oxoanions, including phosphoric acid ion, sulphite acid ion and carbonic acid ion, affect the fluorescence of ß-CD-QDs. Among them, H(2)PO(4)(-) exhibited the largest quenching effect. For the polyprotic acids (HO)(3)AO, the effect of acidic anions on the fluorescence of ß-CD-QDs was in the order: monoanion (HO)(2)AO(2)(-) > dianion (HO)AO(3)(2-) >> trianion AO(4)(3-). After photoactivation for several days in the presence of anions at alkaline pH, the ß-CD-QDs exhibited strong fluorescence emission. The effect of various heavy and transition metal ions on the fluorescence properties of the ß-CD-QDs was investigated further. It was found that Ag(+), Hg(2+) and Co(2+) have significant quenching effect on the fluorescence of the ß-CD-QDs. The Stern-Volmer quenching constants increased in the order: Hg(2+) < Co(2+)

Ternary Cocrystals with Large Soft Cavities: A 1,4-diiodotetrafluorobenzene (DITFB)⋠4-Biphenylpyridine N-oxide (BPNO) Host Assembled by Inclusion of Planar Aromatic Guests.

A large soft-cavity host composed of 1,4-diiodotetrafluorobenzene (DITFB) and 4-biphenylpyridine N-oxide (BPNO) is assembled under the mediation of a planar aromatic guest molecule (pyrene or perylene) through C-I⋅⋅⋅- O-N+ halogen bonds and π-hole⋅⋅⋅π bonds. Single-crystal X-ray diffraction reveals that guest molecules can be completely encapsulated in the four-layer host cavity to assemble ternary host-guest cocrystals; namely, Pyr@DITFB ⋅ BPNO and Per@DITFB ⋅ BPNO. The luminescence of these ternary cocrystals originates from their discrete guest molecules, which exhibit pure-blue and yellow emissions, respectively, that are localized at 425 nm and in the range of 485 to 578 nm, respectively. In addition, the contribution of different fragments to the stabilization of the crystal structure is estimated by computational chemistry. These cocrystals have significant potential for use in optical applications or materials, such as photonics or organic light-emitting diodes, respectively, that require to avoid the aggregation between luminophores.

Structural and luminescent properties of co-crystals of tetra-iodo-ethyl-ene with two aza-phenanthrenes.

Two new co-crystals, tetra-iodo-ethyl-ene-phenanthridine (1/2), 0.5C2I4·C13H9N (1) and tetra-iodo-ethyl-ene-benzo[f]quinoline (1/2), 0.5C2I4·C13H9N (2), were obtained from tetra-iodo-ethyl-ene and aza-phenanthrenes, and characterized by IR and fluorescence spectroscopy, elemental analysis and X-ray crystallography. In the crystal structures, C-I⋯π and C-I⋯N halogen bonds link the independent mol-ecules into one-dimensional chains and two-dimensional networks with subloops. In addition, the planar aza-phenanthrenes lend themselves to π-π stacking and C-H⋯π inter-actions, leading to a diversity of supra-molecular three-dimensional structural motifs being formed by these inter-actions. Luminescence studies show that co-crystals 1 and 2 exhibit distinctly different luminescence properties in the solid state at room temperature.

π-ring-hole bond around difluoroethyne: stabilization of hydrogen bonding cyclohexamer and dicyclohexamer of ammonia molecules.

The present paper displays new supramolecular structural forms of ammonia molecules. The computation reveals that two novel threading structures of C2F2·(NH3)6 and C2F2·(NH3)12 can be assembled between difluoroethyne and ammonia molecules, in which cyclohexamer (NH3)6 and dicyclohexamer (NH3)12 are constructed by robust N-H···N hydrogen bonds and stabilized all by π-ring-hole···N bonds as supporting spokes of annular structures. More interestingly, annular structures of NH3 still maintain stability as C2F2 is removed. Additionally, the electronic properties and nature of the related noncovalent bonds are explored, which illuminate the important role of π-ring-hole bond for the stabilization of annular structures of NH3. This study could provide valuable insights into chemistry of ammonia, new energy and astronomy aspects by single or multiple noncovalent interactions.Graphical abstract Ammonia molecules can exist stably in dodecahedral cage C2F2·(NH3)12 and (NH3)12 via N-H···N hydrogen bonds and π-ring-hole···N bonds.

1,3,5-Trifluoro-2,4,6-triiodobenzene: A neglected NIR phosphor with prolonged lifetime by σ-hole and π-hole capture.

Room temperature phosphorescence (RTP) materials have become a hot topic in fields of organic light-emitting dioes, biological sensing and imaging. The present work reports firstly that 1,3,5-trifluoro-2,4,6-triiodobenzene (TITFB) can act as a simple pure organic NIR phosphor due to its novel function in promoting n-π∗ transition. Also, TITFB crystal has longer phosphorescence lifetime than other ordinary multiiodoluminophors and TITFB powder. Based on the TITFB crystal structure, σ-hole and π-hole capture mechanism of n-electron is proposed, i.e., the excited state energy is decreased and n-electrons are stabilized to cause slower radiative decay rate due to the restriction of σ-hole and π-hole bond. Both computational and experimental studies support the mechanism. The new electron-capture mode is more conducive to understanding pure organic ultralong lifetime RTP.

Concentration-dependent Br...O halogen bonding between carbon tetrabromide and oxygen-containing organic solvents.

High concentration-dependent halogen bonding, a specific solvent effect between carbon tetrabromide and oxygen-containing organic solvents, including methanol, ethanol, acetone, dioxane, diethyl ether, and tetrahydrofuran, was found to coexist with the general solvent effect when CBr4 was over 7.8 x 10(-3) M approximately 1.6 x 10(-2) M critical concentration range. In contrary, in less than this concentration range, only general solvent effect occurred. The 1:1 stoichiometry of halogen bonding complex between CBr4 and charge donor was testified using the modified Benesi-Hildebrand method. The Mulliken correlation confirmed the charge-transfer (CT) character of the CBr4/solvent associations. The electronic coupling elements (H(DA)) showed that the C-Br...O complexes are most-likely localized, which is named as outer-type complex. Density functional theory (DFT) calculation was performed to predict geometry, surface electrostatic potential, interaction energy, and vibrational frequency in gas phase. The MP2 method was also employed to calculate the formation of the sigma-hole (sigma(h)) bonding complexes between carbon tetrabromide and oxygen-containing organic solvents. The vertical excitation energies of the sigma(h)-bonding complexes were calculated by time-dependent density functional theory (TD-DFT). The experimental and theoretical results showed that sigma(h) bonding might be a more important factor for the halogen bonding complex investigated here than the CT. The results showed that Br...O halogen bonding is a blue-shift type.

Fluorescence sensing of nitric oxide in aqueous solution by triethanolamine-modified CdSe quantum dots.

The water-soluble luminescent CdSe quantum dots were prepared by ligand exchange with triethanolamine (TEA). Oxygen can reversibly enhance the fluorescence of the synthesized quantum dots (TEA-CdSe-QDs) in aqueous solution. Nitric oxide radical (NO) can react easily with dissolved oxygen in water and was found to have a significant quenching effect on the fluorescence of the TEA-CdSe-QDs. The fluorescence responses were concentration-dependent and can be well described by the typical Stern-Volmer equation. A good linear relationship (R(2 )= 0.9963) was observed over the range 5.92 x 10(-7 )to 1.85 x 10(-5) mol/L nitric oxide. Above this concentration was a second linear region ranging from 2.12 x 10(-5) to 1.12 x 10(-4 )mol/L NO with a gentler slope. The detection limit, calculated following the 3sigma IUPAC criteria, was 3.02 x 10(-7 )mol/L. The interference effect of some common interferents such as nitrite (NO2 (-)), nitrate (NO(3) (-)), glucose and l-ascorbic acid on the detection of NO was negligible for the proposed system, demonstrating the potential utility of this probe for the detection of NO in biological systems. The possible mechanism was also discussed.

H-aggregation of cationic palladium-porphyrin as a function of anionic surfactant studied using phosphorescence, absorption and RLS spectra.

Room temperature phosphorescence (RTP) was used as a useful analytical tool to investigate the interaction behavior between tetracationic meso-tetrakis (4-trimethylaminophenyl) porphyrin palladium (Pd-TAPP) and anionic sodium dodecyl sulfate (SDS). UV-vis absorption and resonance light scattering (RLS) were further applied to characterize the system. It was presumably suggested that nonspecific self-aggregates among porphyrins formed considering the relatively high concentration of Pd-TAPP. Furthermore, Pd-TAPP changed from free monomer/nonspecific aggregate to H-aggregate and then to out-micellized monomer/nonspecific aggregate as a function of SDS concentration. The fact that RTP signal enhanced obviously and excitation spectrum was blue-shifted by 1580cm(-1) in energy with respect to energy of free Pd-TAPP monomer demonstrated that 1:4 electrostatic interaction between Pd-TAPP and SDS led to the formation of the premicellar porphyrin-surfactant H-aggregates. The RLS spectrum reviewed that the formed H-aggregates were multiple porphyrin units, and UV-vis spectra revealed that cationic groups of monomers/nonspecific aggregates of Pd-TAPP were electrostatically attracted in favor of the surface of anionic micelles but were not encapsulated within apolar regions of SDS micelles when the concentration of SDS was above its critical micelle concentration (CMC).