Brooker's Merocyanine Research Articles

A clusteroluminescent supramolecular polymer network constructed by pillararene and its application in information encryption

AbstractClusterization‐triggered emissive (CTE) materials have attracted great attention in recent years. The regulation of the emission property of materials with CTE property through supramolecular interactions is an excellent strategy for the construction of smart fluorescent materials. In this work, we have prepared a regulatable supramolecular polymer network with CTE properties through pillararene‐based host−guest interactions. The pillar[5]arene‐grafted poly(methyl methacrylate) (PMMA) showed a classic CTE character. After adding Brooker's merocyanine‐grafted polymer to the solution of the pillar[5]arene‐containing PMMA, the supramolecular polymer network gel formed by the host−guest interactions between pillararene and Brooker's merocyanine guest. This supramolecular network showed brighter fluorescence than the pillar[5]arene‐grafted PMMA in the solid state. In addition, the fluorescence emission of the supramolecular network can be further regulated by pH conditions. After adding an acid, the Brooker's merocyanine‐containing guest polymer was protonated, and the supramolecular network changed to a protonated network through host−guest interactions between protonated Brooker's merocyanine guest and pillararene. Interestingly, the fluorescence was quenched when the supramolecular network turned into the protonated network. After adding a base, the protonated network can convert back to the original network, along with recovery of the fluorescence. Therefore, the regulation of the fluorescence of the supramolecular polymer materials with CTE was successfully realized by pillararene‐based host−guest interactions. Furthermore, this tailorable fluorescent supramolecular polymer network system was applied as an information encryption material.

An Ortho-modification Strategy to Develop Brooker's Merocyanine Probe for Precise Monitoring of pH Changes in Urine.

As a non-invasive body fluid, urine pH is one of the important biomarkers for diseases such as the kidneys. Therefore, rapid and accurate detection of urine pH is of great clinical significance. A novel fluorescent probe (SPPH-Cl) was developed based on Brooker's merocyanine skeleton for pH detection. The pKa of SPPH-Cl was adjusted to 6.55 using a phenolic hydroxyl ortho substitution strategy, therefore, the fluorescence response range of SPPH-Cl to pH covers the urine physiological pH range (4.6-8.0). SPPH-Cl has excellent water solubility, stable recoverability, wide anti-interference capability, and sensitive reactions to pH fluctuations in pure aqueous solutions. SPPH-Cl has succeeded in applying to monitor the pH of volunteer urine samples based on a standard curve established in artificially simulated urine, and the detection results have accuracy comparable to pH meters. Therefore, this work provided a powerful molecule tool for detecting pH in urine samples.

Multiscale Frozen Density Embedding/Molecular Mechanics Approach for Simulating Magnetic Response Properties of Solvated Systems.

We present a three-layer hybrid quantum mechanical/quantum embedding/molecular mechanics approach for calculating nuclear magnetic resonance (NMR) shieldings and J-couplings of molecular systems in solution. The model is based on the frozen density embedding (FDE) and polarizable fluctuating charges (FQ) and fluctuating dipoles (FQFμ) force fields and permits the accurate ab initio description of short-range nonelectrostatic interactions by means of the FDE shell and cost-effective treatment of long-range electrostatic interactions through the polarizable force field FQ(Fμ). Our approach's accuracy and potential are demonstrated by studying NMR spectra of Brooker's merocyanine in aqueous and nonaqueous solutions.

Tuning the solvatochromic inversion of Brooker's merocyanine analogs

The synthesis and spectral behavior of three Brooker's merocyanine (BM) analogs are reported. The solvatochromic effect of the binding position of the phenolate donor group to the pyridinium acceptor ring and the degree of annulation of the acceptor moiety were investigated in pure solvents of varying polarity. All the dyes displayed an inverted solvatochromism. The structural modifications examined modulated the spectral shift ranges in both the negative and positive solvatochromic portions of the general inverted behavior by shortening the former and extending the latter. A second observation, and more remarkable result of the evaluated structural modifications, is the consistent displacement of the solvatochromic inversion point of the dyes toward higher solvent polarities compared to the BM, primarily because of the increase in the dyes' sensitivity to the solvent polarizability SP.

Ferrocene analogs of Brooker's merocyanine: a new library of organometallic inverted solvatochromic dyes

Four organometallic dyes with ferrocene as the electron donor group and pyridinium or quinolinium acceptor groups were synthesized and their spectral behavior was recorded in various solvents with different polarities.

Immobilization of Solvatochromic Dyes on Transparent Cellulose Films: an Improved Method for the Study of Homeopathic Potencies.

Highly diluted and succussed solutions (homeopathic potencies) have been shown to interact with a wide range of solvatochromic dyes based on changes in their UV-visible spectra. Studies so far have involved free dyes in solution, but there is a pressing need to find ways to investigate the potency-dye interaction using isolated dye molecules to ask more searching physico-chemical questions regarding the fundamental nature of potencies. The aims of the present study have been to look for ways to covalently immobilize solvatochromic dyes onto transparent cellulose films and hence be in a position to investigate dye-potency interactions without the complication of dye-dye interactions, including dye aggregation, which can occur with free dyes in solution. To date, a total of nine different dyes have been immobilized on cellulose films using epoxide activation of hydroxyl groups on the cellulose surface. Using this method, studies have begun looking at the time course of potency action on one of these immobilized dyes, Brooker's merocyanine. Results show that the interaction of Arsenicum 10M with this dye consists of three phases-an initial growth phase, a sustained plateau of interaction, and a final decline phase lasting several days. A method has been developed that successfully immobilizes solvatochromic dyes onto transparent cellulose film. These films can then be used in a spectrophotometer to study at a much more detailed level how potencies interact with dyes compared with using free dyes in solution. Results indicate that the information gained in this way provides new insights regarding the fundamental nature of potencies. Specifically, studies using immobilized Brooker's merocyanine with Arsenicum 10M reveal that the lifetime of the potency is much longer than expected and that its action consists of three distinct phases, suggesting a resonant interaction with the dye. How resonant interaction might help to explain the clinical action of potencies is discussed.

Unveiling the relationship between structural and polarization effects on the first hyperpolarizability of a merocyanine dye.

The nonlinear optical response, more specifically the Hyper-Rayleigh Scattering (HRS) response of the Brooker's merocyanine, has been calculated at the time-dependent density functional theory level and rationalized in terms of the structural changes and polarization effects induced by applied external electric fields. The structural change leads to large changes in the HRS response, while only slight variations were observed due to the polarization effects on the fixed quinoid form. Considering both structural and polarization contributions concurrently, the HRS response is dominated by cooperative behavior of those effects for weak and intermediate electric field strengths. At the same time, the competition between both effects was a crucial factor in the region of strong electric fields. The obtained results can lead to an easier understanding for upcoming studies considering more realistic models of solvents where it is not simple to disentangle these contributions.

Fluoroponytailed Brooker's merocyanines: Studies on solution behavior, solvatochromism and supramolecular aggregation

In this investigation, influences on solution behavior and solvatochromism caused by the attachment of a 1H,1H,2H,2H-perfluorooctyl side chain onto derivatives of the well-known Brooker's Merocyanine (BM) chromophore are explored. Starting from either 4-picoline or 2-picoline, the corresponding polyfluoroalkylated o- and p-BM have been synthesized in three steps. For all dyes, UV–Vis measurements were conducted in 21 different solvents. An attempted analysis of solvatochromic properties applying linear fits according to Kamlet-Taft parameters turned out to be partially inconclusive and was only feasible for five of the novel dyes after careful examination of their UV–Vis spectra. The observed changes of the spectral characteristics, in combination with the occurrence of either strong hypsochromic or bathochromic shifts, were too significant to be only ascribable to the influence of the solvating medium. Additionally, the maxima of different dyes in different solvents exposed tendencies to converge at specific wavelengths. Taking into account that both, merocyanines as well as fluorosurfactants are known for their formation of supramolecular assemblies, we suggest that aggregation is responsible for the observed phenomena, although controversially disputed in the preliminary literature concerning BM. To underline our proposal, concentration dependent UV–Vis measurements were supplemented.

Homeopathic Potencies May Possess an Electric Field(-like) Component: Evidence from the Use of Encapsulated Solvatochromic Dyes.

Homeopathic potencies have been shown to interact with a range of solvatochromic dyes to produce spectroscopic changes in the visible region of the electromagnetic spectrum. Furthermore, the nature of the changes observed under different experimental conditions is beginning to limit the number of possible hypotheses that can be put forward regarding the fundamental identity of potencies. The present study uses β-cyclodextrins to encapsulate solvatochromic dyes of widely varying structures. The purpose of this approach is to de-couple the primary dye-potency interaction from any subsequent aggregation effects. Despite large differences in molecular structure between dyes, results show that potencies affect all dyes according to the same fundamental principles. Specifically, positively and negatively solvatochromic dyes collectively respond in opposite and complementary ways to potencies in accordance with the differential stabilisation of their excited and ground electronic states. Under the conditions of encapsulation, positively solvatochromic dyes display a bathochromic shift of, on average, 0.4 nm with a 2% absorbance change, and negatively solvatochromic dyes display a hypsochromic shift of, on average, 0.2 nm with a 1% absorbance change. This behaviour is only ever seen in two situations-where solvent becomes more polar or where an electric field is applied to solutions of dyes. The conditions used in this and previous studies to investigate the interaction of potencies with solvatochromic dyes preclude increased polarity of solvent as being responsible for the observed effects and that an explanation in which potencies carry an electric field (or electric field-like) component is by far the more likely. From the magnitude of the spectral changes induced in the dye Brooker's merocyanine by Arsenicum 10M, an estimate of the strength of the postulated electric field of 1.16 × 107 V/m can be made, which is comparable with the potential difference across cell membranes.

Variation of Donor and Acceptor Strength in Analogues of Brooker's Merocyanine and Generalization to Various Classes of Charge Transfer Compounds.

Derivatives of Brooker's merocyanine (BM) have been investigated, which possess different donors and acceptors and therefore vary their donor-acceptor strength SDA. The 00 energies have been extracted from the spectra and compared. Under basic conditions, where the neutral (merocyanine) form is present, the absorption energies for all compounds are similar, whereas there is a large difference for acidic conditions where the cationic (cyanine) form is present. This behavior could be explained by a simple theoretical model involving the dependence of the excitation energy Δ E01 on SDA. This model can be generalized to describe in a consistent way two different well-known classes of neutral chromophores with a certain degree of charge separation, namely merocyanine I (TICT) and merocyanine II (often betainic) compounds. Merocyanines I are characterized by a medium polar aromatic ground state and a zwitterionic quinoid excited state and hence positive solvatochromism, whereas merocyanines II are formally characterized by a zwitterionic aromatic ground state and a less polar quinoid excited state and, accordingly, by negative solvatochromism. On increasing the donor-acceptor strength SDA sufficiently, merocyanines II can, however, move to the so-called overcritical region with the excited state dominated by the zwitterionic valence bond structure. For many of the merocyanine II molecules investigated here, a weakly positive solvatochromic behavior is observed indicating that the ground state contains less of the zwitterionic valence bond wave function than the excited state and that these compounds belong to the overcritical region. The fluorescence spectra have been analyzed in terms of the Franck-Condon model and confirm these conclusions.

A water-soluble two-dimensional supramolecular organic framework with aggregation-induced emission for DNA affinity and live-cell imaging.

A water-soluble two-dimensional supramolecular organic framework (2D SOF) was prepared via self-assembly of cucurbit[8]uril (CB[8]) and a three-arm flat linker molecule, which contains a benzene ring as the core and three Brooker's merocyanine (BM) analogs as arms. The strong host-guest interactions between BM and CB[8] and the directional head-to-tail stacking modes between the BM arms synergistically led to the formation of a 2D SOF. The structure of the 2D SOF was verified by 1H NMR, 2D 1H NMR NOESY, and DLS characterizations, while the monolayer structure was characterized by Cryo-TEM and AFM measurements. The 2D SOF exhibited an obvious AIE enhancement effect in H2O. In addition, DNA induced photoluminescence enhancement was observed for the monomer. As a result, this AIEgen-based 2D SOF could feature not only as a cell visualizer but also as a tracker for the nucleus in biological imaging due to the dynamic assembly process.

Effect of bulky substituents in the donor and acceptor terminal groups on solvatochromism of Brooker's merocyanine

Comparison of spectral properties of stilbazolium dyes in various solvents has exposed the influence of electrophilic and nucleophilic solvation on their solvatochromism.

Brooker's merocyanine: Comparison of single crystal structures

Brooker's merocyanine and its derivatives are well-studied molecules due to their very interesting optical properties. Merocyanine dyes exhibit different colors in solution depending on the solvent's polarity, pH, aggregation and intermolecular interactions. The synthesis of 1-methyl-4-[(oxocyclohexadienylidene)ethylidene]-1,4-dihydropyridine (MOED) dye yielded a particularly interesting solid state structure where in one crystal lattice, MOED and its protonated form are bound by hydrogen bonding interactions.

Solvatochromism and preferential solvation of Brooker's merocyanine in water-methanol mixtures.

The excitation energy of Brooker's merocyanine in water-methanol mixtures shows nonlinear behavior with respect to the mole fraction of methanol, and it was suggested that this behavior is related to preferential solvation by methanol. We investigated the origin of this behavior and its relation to preferential solvation using the three-dimensional reference interaction site model self-consistent field method and time-dependent density functional theory. The calculated excitation energies were in good agreement with the experimental behavior. Analysis of the coordination numbers revealed preferential solvation by methanol. The free energy component analysis implied that solvent reorganization and solvation entropy drive the preferential solvation by methanol, while the direct solute-solvent interaction promotes solvation by water. The difference in the preferential solvation effect on the ground and excited states causes the nonlinear excitation energy shift. © 2017 Wiley Periodicals, Inc.

Controllable Supramolecular Polymerization Promoted by Host-Enhanced Photodimerization.

In this letter, we report a new method of controllable supramolecular polymerization, taking advantage of host-enhanced photodimerization. The low-molecular-weight supramolecular oligomers were formed by noncovalent complexation between cucurbit[8]urils (CB[8]) and the bifunctional monomers (DBN) with Brooker's merocyanine moiety (MOED) on either end. Interestingly, when irradiated with UV light, the supramolecular oligomers could transform into supramolecular polymers with high molecular weight. The molecular weight of supramolecular polymers could be controlled by varying the irradiation time. It is highly anticipated that this work can enrich the methods on the modulation of supramolecular polymerization.

Three-dimensional reference interaction site model self-consistent field analysis of solvent and substituent effects on the absorption spectra of Brooker's merocyanine.

Solvent and substituent effects on the absorption spectra of Brooker's merocyanine (BM) are investigated using the three-dimensional reference interaction site model self-consistent field method and time-dependent density functional theory. The π-π* excitation energies are computed for BM and its derivative 2,6-di-tert-butyl (di-t-Bu) BM. The behaviors of the computed excitation energies with increasing solvent polarity are in good agreement with those of the corresponding experimental measurements. In addition, analysis of the solute-solvent interaction energies and spatial distribution functions reveals that the effects of the solvent on the absorption spectra are reduced by the steric hindrance of the t-Bu groups. Furthermore, from the difference in the solute-solvent interaction energies of BM and di-t-Bu BM, it is shown that the effect of the t-Bu substituents on the absorption spectrum is greater in high-polarity solvents.

Anionic chromogenic chemosensors highly selective for cyanide based on the interaction of phenyl boronic acid and solvatochromic dyes

Solutions of two solvatochromic dyes, Reichardt's pyridinium N-phenolate betaine (1) and Brooker's merocyanine (2), are colored in acetonitrile but become colorless when phenyl boronic acid (PBA) is added due to the formation of covalently linked dye-PBA species. Of the various anions added, only F− and CN− caused the reappearance of the original color related to the free dye in solution. These anions act as nucleophiles in acetonitrile and displace the dye leaving group. On the addition of very small amounts of water the system becomes highly selective toward CN− because of the ability of water to strongly solvate F−, inhibiting its nucleophilic action, while CN− is sufficiently naked to react with dye-PBA species. The titrations of the dye-PBA complexes with CN− revealed that the shape of the curves is dependent on the experimental conditions. With the use of large amounts of PBA, the dye, after being displaced, interacts with the free PBA forming hydrogen-bonded complexes, which are disrupted with the addition of an excess of the anion. This was not observed in aqueous acetonitrile since water can form hydrogen bonds with the boronic acid and with the dye, preventing the formation of dye-PBA hydrogen-bonded complexes.

A colorimetric and fluorescent dual-channel cyanide ion probe using crosslinked polymer microspheres functionalized with protonated Brooker's merocyanine

This paper describes the development of a colorimetric and fluorescent cyanide probe based on crosslinked polymer microspheres functionalized with a protonated merocyanine. The functionalised microspheres were prepared by free radical polymerization using 4-((E)-2-[(4-hydroxylphenyl) ethenyl-1-allyl pyridinium bromide as the functional monomer, ethylene glycol dimethacrylate as the crosslinker, and azobisisobutylnitrile as the radical initiator. Upon introducing CN– to a suspension of the functionalised microspheres in ethanol/H2O (9:1, v/v), a change from yellow to red and a decrease in fluorescence intensity at 497 nm were immediately observed. This CN– probe can be reversed many times, which is cost efficient and beneficial to the environment. Analytical application of the functionlised microspheres to measure CN– concentration in spiked water samples was explored with good recoveries. Thus, the colorimetric and fluorescent CN− probe has high potential for the ultrasensitive detection of CN− in real samples.

Solvatochromic Shift of Brooker's Merocyanine: Hartree-Fock Exchange in Time Dependent Density Functional Calculation and Hydrogen Bonding Effect.

The Brooker's merocyanine exhibits a large hypsochromic shift from an apolar aprotic solvent to a polar protic solvent. Quantum chemical calculations have been performed to study the solvatochromism, but there remained a discrepancy between the calculated and experimental solvatochromic shifts. In this paper we evaluate quantum mechanically the excitation energies of the Brooker's merocyanine in water, methanol, acetonitrile, and dichloromethane to investigate what are important factors to accurately model the solvatochromism of the dye by using TDDFT in combination with implicit and explicit solvation models including the PCM, PCMSMD, RISM-SCF-SEDD, and mean-field QM/MM. The results severely depend on the density functional, especially on the amount of Hartree-Fock exchange included in the functional. Furthermore, an explicit description of the solute-solvent hydrogen bonds makes a non-negligible contribution to the shift. The experimental large solvatochromic shift can be accurately reproduced by the TDDFT/RISM-SCF-SEDD and mean-field QM/MM calculations with the LC-BOP functional, although the excitation energies in solutions are considerably overestimated. We also estimated the excitation energies and the solvatochromic shift at the SAC-CI/RISM-SCF-SEDD and mean-field QM/MM level, which are in very good agreement with the experimental values. These results indicate that if an explicit solvent model is used, TDDFT calculations using such a long-range corrected functional can accurately model the solvatochromism. However, an ab initio quantum chemical method including sufficient electron correlation effects is required to reproduce not only the solvatochromism but also the excitation energies in solutions.

Optical chemosensor for the detection of cyanide in water based on ethyl(hydroxyethyl)cellulose functionalized with Brooker's merocyanine.

Ethyl(hydroxyethyl)cellulose was functionalized with Brooker's merocyanine. The modified polymer was easily transformed in a film, which could be used as a highly selective chromogenic and fluorogenic chemosensor for the detection of cyanide in water, with detection limits of 1.9 × 10(-5) and 1.0 × 10(-7) mol L(-1). The film was successfully applied to the detection of cyanide in cassava (Manihot esculenta Crantz) roots, which are a well-known source of endogenous biological cyanide.