Hydrogen-bonded dimer stacking induced emission of aminobenzoic acid compounds

Solvatomorphism and first-time observation of acid-acid catemer in 4-phenylamino-benzoic acids

To investigate the polymorphism in 4-phenylamino-benzoic acids (4-PABAs) in general, and the effect on the polymorphism of these compounds exerted by substitution in particular, a series of 4-PABAs (1-8) varying in the substitution position and pattern were synthesized, and their polymorphic behavior was investigated for the first time. A relatively comprehensive polymorph screening led to the discovery of two forms, one solvent-free and the other solvate, for compounds 1, 3 and 8, and one form for the other compounds. The crystal structures were determined by single-crystal XRD. All the 4-PABAs in the crystal structures are highly twisted, and all the solvent-free crystals are based on the conventional acid-acid dimer motif, except for 2, which has a rarely observed acid-acid catemer motif. Two of the solvates (1-S and 8-S) have pyridine in the lattice while the other (3-S) has dichloromethane. The observation indicates that neither conformational flexibility or substitution alone nor the combination of both leads to polymorphism in these compounds, which is in dramatic contrast to the polymorphism of fenamic acids. The thermal properties of each system were investigated by differential scanning calorimetry and desolvation of the solvates was studied by thermogravimetric analysis. Hirshfeld surface analysis and molecular dynamics simulation were performed to study the mechanism of polymorphism and the intermolecular interactions contributing to the formation and stability of each crystal form.

Double substitution leads to a highly polymorphic system in 5-methyl-2-m-tolylamino-benzoic acid

Substitution on both aromatic rings of fenamic acid led to a highly polymorphic system in 5-methyl-2-m-tolylamino-benzoic acid, in contrast to the two mono-substituted analogs, which had only one or two forms obtained.

Envisioning Quantum Electrodynamic Frameworks Based on Bio-Photonic Cavities

A bio-photonic cavity quantum electrodynamic (C-QED) framework could be imagined as a system in which both the “cavity” and the “atom” participating in the light-matter interaction scenario are bio-inspired. Can a cavity be made of a bio-polymer? If so, how should such a cavity appear and what are the best polymers to fabricate it? Can a bioluminescent material stand the comparison with new-fashion semiconductors? In this review we answer these fundamental questions to pave the way toward an eco-friendly paradigm, in which the ever-increasing demand for more performing quantum photonics technologies meets the ever-increasing yet silent demand of our planet to reduce our environmental footprint.

The Crystal Structure and Intermolecular Interactions in Fenamic Acids-Acridine Complexes

In order to improve pharmaceutical properties of drugs, complexes are synthesized as combinations with other chemical substances. The complexes of fenamic acid and its derivatives, such as mefenamic-, tolfenamic- and flufenamic acid, with acridine were obtained and the X-ray structures were discussed. Formation of the crystals is determined by the presence of the intermolecular O–H^…N hydrogen bond that occur between fenamic acids and acridine. Intermolecular interactions stabilizing the crystals such as π^…π stacking, C–H^…X (X = O, Cl) intermolecular hydrogen bonds as well as C–H^…π and other dispersive interactions were analyzed by theoretical methods: the quantum theory of atoms in molecules (QTAIM) and noncovalent interaction (NCI) approaches.

Hydrogen-bond-driven dimers of naphthyridine derivatives for selective identification of DNA G-quadruplexes

G-quadruplex (GQ) ligands as potential anti-cancer drugs have received extensive attention. Large aromatic systems are usually considered in the design of the ligands to improve the binding with GQs, which are typically constructed by the combination of small modules with covalent bonds. In this study, we presented a non-covalent bond approach to construct GQ ligands with an extended planar structure. The ligands were stable dimers assembled through quadruplex intermolecular hydrogen bonds between two molecules of naphthyridine derivatives. Spectroscopic analyses showed that dimeric ligands could stabilize GQs with an increase of the melting temperature up to 12 °C and induced conformational conversion of hybrid GQs. Confocal fluorescence microscopy confirmed the enrichment of naphthyridine ligands in the nucleus. The ligands showed moderate cytotoxicity against HeLa cells with an IC50 value of 7.5 μg mL-1 and effectively induced growth inhibition and apoptosis in HeLa cells. These results confirmed the feasibility of the quick building of GQ ligands through intermolecular interactions of simple molecules that are easily obtained during synthesis, which is helpful for GQ ligand design and quick establishment of a ligand library through the self-assembly of easily available molecular components.

One-Step Preparation of Hyperbranched Polyether Functionalized Graphene Oxide for Improved Corrosion Resistance of Epoxy Coatings

In this paper, hyperbranched polyether functionalized graphene oxide (EHBPE-GO) was prepared by a facile one-step method. Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), thermogravimetric analyzer (TGA), and trans-mission electron microscopy (TEM) results confirmed the formation of EHBPE-GO. Then, EHBPE-GO was cured with phenolic amides at room temperature to prepare epoxy coatings. The corrosion resistance of epoxy coatings was investigated systematically by using electrochemical and traditional immersion methods. Results show that a small amount of EHBPE-GO (8 wt % of Diglycidyl ether of bisphenol A (DGEBA)) in epoxy coating achieves 50% higher improvement in acid-resistance than unmodified neat DGEBA resin. For the nanocomposite epoxy coating, the superior acid-resistance is attributed to the increased crosslink density and the impermeable 2D structure of EHBPE-GO. This work provides a facile strategy to develop the effective improved corrosion resistance nanofiller for epoxy coating.

Spectral studies of niflumic acid aggregation in dissolved, solid and adsorbed states

FTIR spectra of niflumic acid in solid state, dissolved in CCl₄ and adsorbed on silica or alumina surface, as well as their temperature dependence, provide information about different stages of aggregation: monomers, dimers, amorphous and crystalline solid phase, as well as about perturbation of the molecule by the surface. The spectra observed are compared with those obtained by quantum mechanical calculations. The luminescence spectra are less sensitive to the aggregation, they differ mostly in the intensity, while the position of maximum at about 440 nm remains almost the same.

Effect of Conjugation Mode on Intramolecular Charge Transfer in Fabricating Acid-Responsive Fluorophores

Solid-state acid-responsive materials are promising for the tunability of their intrinsic properties. However, the relationship between molecular structure and emission shift as a response to acid stimuli has not been systematically studied. Herein, we report the effect of protonation and subsequent intramolecular hydrogen bonding on the photophysical properties of compounds (MPP-s, MPP-d, and MPP-d-CN) with different conjugation modes between the electron-donating dimethoxyl phenyl and the electron-withdrawing benzothiazole ring. The results established that the stronger the intramolecular charge transfer feature of the compound, the smaller is the emission shift after acid stimuli. Our studies also indicated that the conjugation mode significantly affected the solid-state packing mode: MPP-s and MPP-d tended to form dimers, while MPP-d-CN exhibited the strongest aggregation-induced emission enhancement (AIEE). The exploration of structure-property relationship would provide experimental and theoretical guidance in designing acid-responsive molecular switches and developing high-performance AIEE-active luminogens.

Supramolecular Mimic for Bottlebrush Polymers in Bulk

A series of poly(tetrahydrofuran)s with molecular weights above entanglement molecular weight M _e were synthesized, and one of their end-groups was functionalized with a supramolecular entity so that the corresponding polymers form a brushlike structure suitable for comparison with conventional irreversible bottlebrush polymers. To compare their relaxation mechanisms, linear rheology was employed and showed that a hierarchical relaxation, which is usually observed in bottlebrush polymers, occurs in these materials, too. The polymer chain segments close to the supramolecular backbone are highly immobilized due to strong association in the center of polymer brush and cannot relax via reptation mechanism, which is mainly responsible for linear entangled polymer relaxations. Therefore, disentanglement can take much longer through contour length fluctuations and arm retraction processes similar to covalent bottlebrush polymers and combs. The relaxed ends of polymers then act as solvent to let the remaining segments of the polymeric brush undergo Rouse-like motions (constraint release Rouse). At longer times, additional plateau appears, which can be attributed to the relaxation of the entire supramolecular bottlebrush polymer via hopping or reptative motions. With an increase of temperature, viscoelastic solid behavior turns into viscoelastic liquid due to reversible depolymerization of the supramolecular backbone of the bottlebrush polymer. The elastic modulus (G' in the order of kPa) was much less than the values found for the entanglement plateau modulus of linear poly(tetrahydrofuran) (in order of MPa). This low modulus value, which exists up to very low frequencies (high temperatures), makes them a good candidate for supersoft elastomers.

The Na-O bond in sodium fenamate

The one-dimensional polymeric structure of sodium diaquafenamate-water (1/1) was studied by X-ray diffraction. The sodium cation is coordinated to one oxygen atom of the carboxylate group and to four water oxygen atoms. To characterize the Na-O bonds, the quantum theory of atoms in molecules (QTAIM) and noncovalent interaction (NCI) approaches have been used. Both methods confirmed that the Na-O bonds are very weak, comparable with the weak N-H...O intramolecular hydrogen bond. The polymeric structure is stabilized by the interaction of the sodium cation with the surrounding water molecules.

Chlorine (Cl) - Substituted Carbazole Based A-π-D-π-a Push-Pull Chromophores as Aggregation Enhanced Emission (AEE) Active Viscosity Sensors: Synthesis, DFT and NLO Approach

Three new carbazole functionalized A-π-D-π-A extended chromophores 4a, 4b and 4c comprising of different chemical functional groups on C=C bond with the assistance of chlorovinylene group in π-conjugation are synthesized and investigated spectroscopically. We have investigated the effect of different electron acceptors - carboxycyanomethylene, dicyanomethylene and 2-(benzothiazol-2-yl) cyanomethylene, the effect of the insertion of chlorine in π-conjugation on photophysical properties and the effect of double acceptors. The chromophores 4a, 4b and 4c exhibited positive solvatochromism with large Stokes shifts and bright orange to red solid-state fluorescence. Amongst all the three compounds 4c exhibited maximum emission wavelength at 615 nm in DMSO. They presented characteristic twisted intramolecular charge transfer (TICT) emission. Observations exhibited that 4c containing long hexyl group in donor unit and 2-(benzothiazol-2-yl) cyanomethylene as an acceptor group formed an aggregate in the mixture of solvents and exhibited better aggregation enhanced emission (AEE) compared to the other two derivatives. Amongst the three styryls, 4c showed the highest emission intensity 299 a.u. at 90% water:DMF fraction (f_w). Chromophores 4a-4c also exhibited good fluorescence response towards viscosity. Among the three fluorescent molecular rotors (FMR), 4c exhibited excellent viscosity sensitivity with x value = 0.687. The Non-linear (NLO) characters are estimated with the help of solvatochromic and computational methods using the functionals, B3LYP and CAM-B3LYP. The dyes showed large "linear polarizability (α_CT)", "first order hyperpolarizability" (β) and "second order hyperpolarizability" (γ) values which show that synthesized styryls can be used as a "NLO" material. The α_CT, β and γ for 4c are found to be the maximum amongst the all three dyes which can be ascribed to the smaller band gap apparent from experimental as well as DFT method.

Aggregation-induced emission and polymorphism/shape/size-dependent emission behaviours of fenamates for potential drug evaluation

Aggregation-induced emission and polymorphism/shape/size-dependent emission behaviors were found coexisting in fenamates, which provides a novel approach toward future drug evaluation.

(E)-4-Methyl-N-((quinolin-2-yl)ethylidene)aniline as ligand for IIB supramolecular complexes: synthesis, structure, aggregation-induced emission enhancement and application in PMMA-doped hybrid material

Judicious structural design employing 2-quinolinecarboxaldehyde and 4-methylaniline was used to generate the Schiff base ligand (E)-4-methyl-N-((quinolin-2-yl)ethylidene)aniline (L). Five IIB complexes, namely, [ZnLCl₂] (1), [ZnL(NO₃)₂] (2), [ZnL(OAc)₂]₃ (3), [CdL(OAc)₂]₃ (4), and [HgLCl₂] (5) have been synthesized based on L. Single-crystal X-ray diffraction analysis indicates that complexes 1, 3 and 4 exhibit 3D networks, whereas 2 and 5 form 2D layers and 1D chains, respectively. TD-DFT calculations show a good correlation with the UV-vis absorption assigned to π → π* intraligand transitions. Furthermore, complexes 1-5 displayed strong greenish luminescent emissions (518-524 nm) in the aggregate state but weak emissions in solution (aggregation-induced emission enhancement), which may be due to the existence of C-HCl/O hydrogen bonding and ππ stacking interactions, resulting in restriction of intramolecular rotation (RIR). Variable-concentration ¹H NMR studies suggested that the aggregates undergo intramolecular changes in conformation due to intermolecular interactions. Moreover, the emission intensity and lifetime exhibited obvious increases induced by mechanical grinding and temperature reduction, which were also attributed to AIEE properties. Subsequently, complex 1 was incorporated into poly(methyl methacrylate) (PMMA), whereby 1-PMMA exhibited enhanced emission intensity (20-fold increase in comparison with that of 1), which offers opportunities for use in plastic greenhouses to increase leaf photosynthesis.

Quantitative analysis of weak non-covalent interactions in (Z)-3-(4-halophenyl)-2-(pyridin-2/3/4-yl)acrylonitriles

A detailed experimental and theoretical investigation on the intermolecular interactions in (Z)-3-(4-halophenyl)-2-(pyridin-2/3/4-yl)acrylonitriles is reported and different π staking motifs observed in these structures.

Two intensified fluorescence colors' switching achieved by branched dye nanoaggregates

In this study, a variety of branched target dyes containing double internal proton transfer segments were synthesized. For comparison, some linear analogs including a single internal proton transfer part were synthesized. The corresponding reference molecules lacking proton transfer segments were also prepared. The properties and aggregation modes of these dye aggregates were investigated on the basis of scanning electron microscopy images, transmission electron microscopy images, dynamic light scattering, X-ray diffraction, UV/visible absorption spectra and fluorescence emission spectra. The results showed that molecular aggregates with the morphologies of nano-scaled rounded or cubic particles of the target branched dyes could be yielded in mixed organic solvent/H₂O solution. A remarkable emission enhancement and fluorescence switching process (from bright yellow to luminous pure blue) under 365 nm lamp irradiation was observed for these target branched dye nanoaggregates. However, no aggregates of the reference branched dyes free of hydroxyl groups were formed and no obvious spectral variations were found. In contrast, all the studied linear dyes yielded molecular nanoaggregates in mixed organic solvent/H₂O solution, and only intensified single normal blue fluorescence emission was presented. This study provided real examples of some branched organic dye aggregates which were capable of displaying naked-eye enhanced fluorescence color switching under an UV lamp.

Novel Hydrogen-Bonding Cross-Linking Aggregation-Induced Emission: Water as a Fluorescent "Ribbon" Detected in a Wide Range

The development of efficient sensors for detection of the water content in a wide detection range is highly desirable for balance in many industrial processes and products. Presented herein are six novel different substituted Schiff base Zn(II) complexes, which exhibit the remarkable capability to detect traces of water in a wide linear range (most can reach 0-94%, v/v), low detection limit of 0.2% (v/v), and rapid response time of 8 s in various organic solvents by virtue of an unusual water-activated hydrogen-bonding cross-linking AIE (WHCAIE) mechanism. As a proof-of-concept, the WHCAIE mechanism is explained well by single X-ray diffraction, absorption spectra, fluorescence spectra, dynamic light scattering, ¹H NMR spectra, and theoretical calculations. In addition, the molecules demonstrated their application for the detection of humidity (42-80%). These Schiff base Zn(II) complexes become one of the most powerful water sensors known due to their extraordinary sensitivity, fast response, and wide detection range for water.

Coordination-Directed Stacking and Aggregation-Induced Emission Enhancement of the Zn(II) Schiff Base Complex

2-(Trityliminomethyl)-quinolin-8-ol (HL) and its Zn(II) complex were synthesized and characterized by single-crystal X-ray diffraction. HL is an unsymmetrical molecule and coordinated with Zn(II) ion to form ZnL₂ in the antiparallel-mode arrangement via Zn-O (hydroxyl group) and Zn-N (quinoline ring) of HL. A high degree of ZnL₂ molecules ordering stacking is formed by the coordination bonds and intermolecular π-π interactions, in which head-to-tail arrangement (J-mode stacking) for L^- is found. HL is nonfluorescent and ZnL₂ is weakly fluorescent in THF. The fluorescence emission of ZnL₂ enhances in THF/H₂O as H₂O% (volume %) is above 60% and aggregates particles with several hundred nanometers are formed, which is confirmed by DLS data and TEM images. The J-aggregates stacking for L^- in ZnL₂ results in aggregation-induced emission enhancement (AIEE) for ZnL₂ in THF/H₂O. Theoretical computations based on B3LYP/6-31G(d, p) and TD-B3LYP/6-31G(d, p) methods were carried out. ESIPT is the supposed mechanism for fluorescent silence of HL, and fluorescence emission of ZnL₂ is attributed to the restriction of ESIPT process. The oscillator strength of ZnL₂ increases from 0.017 for monomer to 0.032 for trimer. It indicates that a high degree of ZnL₂ molecules ordering stacking in THF/H₂O is of benefit to fluorescence enhancement. HL is an ESIPT-coupled AIEE chemosensor for Zn(II) with high selectivity and sensitivity in aqueous medium. HL can efficiently detect intracellular Zn(II) ions because of ESIPT-coupled AIEE property of ZnL₂ in mixed solvent.

Supramolecular networks in molecular complexes of pyridine boronic acids and polycarboxylic acids: synthesis, structural characterization and fluorescence properties

3- and 4-pyridineboronic acids have been combined with trimesic and pyromellitic acids to give three molecular complexes.

The Crystal Structure and Behavior of Fenamic Acid-Acridine Complex Under High Pressure

The crystal structure of fenamic acid-acridine complex is determined by X-ray diffraction. The strong OHN hydrogen bond linking the complex components and other interactions responsible for packing of the molecules into a crystal are investigated within the Quantum Theory of Atom in Molecule theory. The crystal structure is compared with the structure optimized at B3LYP/6-311++G** level and with the theoretical structures optimized under systematically changed pressure. Analysis of the lattice constants, hydrogen bond lengths, and angles of the inter- and intramolecular hydrogen bond under compression is performed. The structural transformation observed at 5 GPa is connected with a change in the intermolecular OHN hydrogen bond. The proton shifts to acceptor and a new interaction in the crystal appears.

Fluorescent aliphatic hyperbranched polyether: chromophore-free and without any N and P atoms

The strong fluorescence, in both the solution and the bulk state, of a chromophore-free aliphatic hyperbranched polyether which does not contain N and P atoms was reported for the first time. Effects of concentration and solvent solubility were measured. Its ethanol solution shows a strong blue-green fluorescence (Yu = 0.11-0.39), and its fluorescence shows a strong selective quenching with respect to Fe(3+).

Hydrogen bond-assisted aggregation-induced emission and application in the detection of the Zn(ii) ion

The compounds of 3-aminopyridine-2-carboxylic acid with K(+) (1) and Zn(2+) (2) were found to be AIE-active. The AIE behaviours could be attributed to the restriction of intramolecular rotation (RIR) and vibration (RIV) via hydrogen bonds, resulting in rigidity enhancement of the molecules. An AIE-based fluorescence turn on chemosensor for the Zn(ii) ion has been developed in aqueous media with high selectivity and sensitivity.

Excited-state intramolecular proton-transfer (ESIPT)-inspired solid state emitters

Solid state emitters based on excited state intramolecular proton transfer (ESIPT) have been attracting considerable interest since the past few years in the field of optoelectronic devices because of their desirable unique photophysical properties. The photophysical properties of the solid state ESIPT fluorophores determine their possible applicability in functional materials. Less fluorescence quantum efficiencies and short fluorescence lifetime in the solid state are the shortcomings of the existing ESIPT solid state emitters. Designing of ESIPT chromophores with high fluorescence quantum efficiencies and a long fluorescence lifetime in the solid state is a challenging issue because of the unclear mechanism of the solid state emitters in the excited state. Reported design strategies, detailed photophysical properties, and their applications will help in assisting researchers to overcome existing challenges in designing novel solid state ESIPT fluorophores for promising applications. This review highlights recently developed solid state ESIPT emitters with focus on molecular design strategies and their photophysical properties, reported in the last five years.

Crystal induced phosphorescence from Benz(a)anthracene microcrystals at room temperature

Pure organic compounds that are also phosphorescent at room temperature are very rare in literature. Here, we report efficient phosphorescence emission from aggregated hydrosol of Benz(a)anthracene (BaA) at room temperature. Aggregated hydrosol of BaA has been synthesized by re-precipitation method and SDS is used as morphology directing agent. Morphology of the particles is characterized using optical and scanning electronic microcopy (SEM). Photophysical properties of the aggregated hydrosol are carried out using UV-vis, steady state and time resolved fluorescence study. The large stoke shifted structured emission from aggregated hydrosol of BaA has been explained due to phosphorescence emission of BaA at room temperature. In the crystalline state, the restricted intermolecular motions (RIM) such as rotations and vibrations are activated by crystal lattice. This rigidification effect makes the chromophore phosphorescent at room temperature. The possible stacking arrangement of the neighboring BaA within the aggregates has been substantiated by computing second order Fukui parameter as local reactivity descriptors. Computational study also reveals that the neighboring BaA molecules are present in parallel slipped conformation in its aggregated crystalline form.

Symmetric and unsymmetric thienyl-substituted fluorenone dyes: static excimer-induced emission enhancement

In this work, we designed and synthesized four symmetric and asymmetric thienyl-substituted fluorenone compounds, which all exhibited typical AIE properties.

Detection of cyanide by a novel probe with a V-shaped structure based on aggregation of the probe adduct

A novel V-shaped probe is reported with extremely rapid response, high selectivity and very low detection limit to cyanide anions in aqueous solution based on the intensely emissive aggregates of the probe adduct.

Hydrosoluble aliphatic tertiary amine-containing hyperbranched polysiloxanes with bright blue photoluminescence

Two hydrosoluble aliphatic tertiary amine-containing hyperbranched polysiloxanes are explored. The resulting conventional chromophore-free polymers, without any treatment, such as acidification or oxidation, can emit bright blue fluorescence.

Crystallization-induced dual emission from metal- and heavy atom-free aromatic acids and esters

Pure organic materials exhibiting room temperature phosphorescence (RTP) have significant fundamental importance and promising optoelectronic and biological applications. Exploration of metal- and heavy atom-free pure organic phosphors, however, remains challenging because achieving emissive triplet relaxation that outcompetes the vibrational loss is difficult without metal or heavy atoms. In this contribution, in contrast to aggregation-caused quenching (ACQ) normally observed in conventional chromophores, a unique phenomenon of crystallization-induced dual emission (CIDE), namely, simultaneously boosted fluorescence and phosphorescence upon crystallization, is observed in a group of pure organic aromatic acids and esters at ambient conditions. Moreover, two triplet-involved relaxations of delayed fluorescence (DF) and phosphorescence are activated. Such efficient intrinsic emission from both singlet and triplet states in a single compound without employing metal or heavy atoms is suitable for a variety of fundamental research and applications.

Study on the solution and solid-state fluorescence of novel BF2 complexes with (Z)-2-[phenanthridin-6(5H)-ylidene]-1-phenylethanone and its derivatives as ligands

A family of novel N,O-chelated BF₂ complexes with intense solution and solid-state emission were synthesized and their photophysical properties were studied.

Fluorinated anthracene derivatives as deep-blue emitters and host materials for highly efficient organic light-emitting devices

Novel fluorinated anthracene based deep-blue-emitting molecules, namely 9,10-bis-(n′-fluoro-biphenyl-3-yl)-anthracene (nF-DPAs), have been designed and synthesized by a Suzuki cross-coupling reaction.

Easily fixed simple small ESIPT molecule with aggregation induced emission for fast and photostable “turn-on” bioimaging

An easily fixed simple small ESIPT molecule with aggregation induced emission has been demonstrated for fast and photostable “turn-on” bioimaging.

How is the AIE mechanism profoundly changed in an ESIPT family: the novel introduction of a tetraphenylethene group onto (Z)-3-(quinolin-2-ylmethylene)-3,4-dihydroquinoxalin-2(1H)-one

The first example showing that the AIE mechanism can be completely changed from restriction of TICT to RIR by the introduction of a tetraphenylethene group onto a molecule with ESIPT character is reported herein.

Solvatochromic and application in dye-sensitized solar cells of sandwich-like Cd(ii) complexes: supramolecular architectures based on N1,N3-bis[(6-methoxypyridin-2-yl)methylene]benzene-1,3-diamine

Co-sensitizers 1 and 2 exhibited solvatochromism and fluorescence quenching behavior to CH₃OH.