Substituent Modulation from ESIPT to ICT Emission in Benzoimidazolphenyl-methanones Derivatives: Synthesis,Photophysical and DFT Study

Design and synthesis of five new derivatives of benzophenone based imidazole dyes is presented. Synthesized dyes were well characterized by ¹H NMR, ¹³C NMR, FT-IR and mass analysis. Dyes contain a secondary acceptor, ESIPT core and different donors forming (D-ESIPT core-A) as basic skeleton in order to study both ESIPT and ICT systematically in this same class of dyes. Dyes without a donor substituent showed ESIPT emission while dyes with a substituted strong donor showed intramolecular charge transfer (ICT) emission. Moreover emission properties of methoxy analogue dyes has been studied to further confirm non-ESIPT emission in dyes without donors and ICT emission in strong donor substituted dyes. All dyes exhibited long range emissions from 392 to 567 nm. Dyes exhibiting ESIPT emission showed negative solvatochromism while ICT emission exhibiting dyes shows positive solvatochromism. ICT and ESIPT characteristics are well correlated with polarity functions plots and Mulliken–Hush analysis. Experimental observations are well supported by TD–DFT and computed energies. The electrophilicity index has been calculated to get details of the stabilities of possible tautomers.     

Electronic effect on the optical properties and sensing ability of AIEgens with ESIPT process based on salicylaldehyde azine

Two novel AIE-active salicylaldehyde azine(SAA) derivatives with a typical excited-state intramolecular proton transfer(ESIPT) process are prepared by introducing electron-withdrawing and donating groups at para-position of phenolic hydroxyl group(CN-SAA and TPA-SAA). The effect of the proton activity in SAA framework on their optical behaviors is investigated spectroscopically. The results from NMR and solvation measurements show that the proton of phenolic hydroxyl group has higher activity when there are electron-withdrawing groups, and the absorption and fluorescence spectra in buffers with different pH also provide the same results. After inviting F. as a nucleophilic probe, this proton activity difference in CN-SAA and TPA-SAA becomes more obvious. The potential application of both molecules is investigated. TPA-SAA exhibits good quantitative sensing ability towards F. with a fluorescence "turn-on" mode, whereas the aggregates of TPA-SAA can selectively and sensitively detect Cu2+ in aqueous solution. From these results, a structure-property relationship is established: the occurrence of ESIPT process will become much easier when linking electron-withdrawing groups at the para-position of phenolic hydroxyl group(e.g., CN-SAA),and it is better to introduce electron-donating groups to enhance the sensing ability towards ions(e.g., TPA-SAA). This work will provide guidance for further design and preparation of AIE-active luminogens with ESIPT process for sensing applications.     

On the inoperativeness of the ESIPT process in the emission of 1-hydroxy-2-acetonaphthone: a reappraisal

For a molecule which contains an intramolecular hydrogen bond (IMHB) in its chemical structure to undergo an excited singlet intramolecular proton transfer (ESIPT) process, on photoexcitation, there must occur a simultaneous increase, in a substantial manner, in the acidity of the proton donor and the basicity of the proton acceptor forming the IMHB [J. Am. Chem. Soc. 2001, 123, 11940]. For the reason that those changes occur on photoexcitation of the 2-hydroxyacetophenone but not for 1-hydroxy-acetonaphthone, one draws the conclusion that, while ESIPT is operative in the 1(pi,pi*)(1) electronic state of the monocyclic compound 2-hydroxyacetophenone, it is not operative in its bicyclic homolog 1-hydroxy-2-acetonaphthone. We have shown the photophysics of 1-hydroxy-2-acetonaphthone in its first excited electronic state to be governed by two stable, easily reconverted enol structures, the presence of which causes the peaks in the free-jet fluorescence excitation spectrum for the compound to split into two of similar strength. In this paper, we rationalize photophysical evidence for 1-hydroxy-2-acetonaphthone obtained by femtosecond spectroscopy over the past 13 years in the light of existing photophysical patterns based on steady-state spectra for the compound [J. Am. Chem. Soc. 1993, 115, 4321].     

Synergistic effect of two solvents, tert-alcohol and ionic liquid, in one molecule in nucleophilic fluorination

We have demonstrated the synergistic effect in nucleophilic fluorination when we combined two solvents--ionic liquid (IL) and tert-alcohol--into one molecule. Consequently, these functionalized ILs not only increase the nucleophilic reactivities of the fluoride anion but also remarkably reduce the olefin byproduct. Although the mechanism of this synergistic effect remains to be elucidated, we have illustrated the possibility of solvent engineering for a specific reaction.     

Spectrofluorometric studies on the binding interaction of bioactive imidazole with bovine serum albumin: a DFT based ESIPT process

Bioactive imidazole derivatives were synthesized and characterized by NMR spectra, mass and CHN analysis. An excited state intramolecular proton transfer (ESIPT) process in hydroxy imidazole has been studied using emission spectroscopy. In hydrocarbon solvent, the tautomer emission predominates over the normal emission and in alcoholic solvent like ethanol; a dramatic enhancement of normal emission is observed which was due to increased solvation. DFT calculation on energy, charge distribution of the rotamers in the ground and excited states of the imidazole derivative were performed and discussed. PES calculation indicates that the energy barrier for the interconversion of two rotamers is too high in the excited state than in the ground state. The interaction between bioactive imidazole derivative and bovine serum albumin (BSA) was investigated.     

Observation of the missing mode effect in a poly-phenylenevinylene derivative: effect of solvent, chain packing, and composition

Optical emission spectra of poly[2-methoxy-5-[3('),7(')-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) in dilute solutions exhibit a vibronic progression interval (～1225?cm(-1)) that does not correspond to any ground state vibrational mode frequency. This phenomenon is assigned as the missing mode effect (MIME) in which five key displaced polymer backbone vibrational modes in the range of 800-1600?cm(-1) contribute to the MIME interval. Emission spectra are calculated by analytically solving the time-dependent Schro?dinger equation using estimates of mode-specific vibrational displacements determined independently from preresonance Raman intensities. Emission spectra of MDMO-PPV thin films and nanoparticles are measured and lineshapes show an increase of the MIME frequency to ～1340?cm(-1) in addition to changes in vibronic intensity distributions and energies. Composite blend thin films consisting of MDMO-PPV and a fullerene derivative (1:1 w/w) exhibit a substantially larger MIME interval (～1450?cm(-1)) that arises from an increase in polymer chain planarity. This structural change is most apparent from large decreases of the excited state displacement of an out-of-plane C-H bending mode (961?cm(-1)) that becomes forbidden in the planar structure.     

Electrochromism based on the charge transfer process in a ferrocene-BODIPY molecule

A new type of donor-acceptor molecule DiFc-B combined ferrocene and BODIPY unit has been synthesized, and the NMR spectra, photophysical property, and electrochemical property were studied. The in situ spectro-electrochemical experiment was carried out, a notable absorption change had been observed under oxidative potential, and a recovery could happen under reductive potential and this process could repeat for several times. Such a phenomenon also happened when oxidative metal ion was added into the solution of DiFc-B. In order to study the mechanism of the electrochromism, the theoretical calculation was performed, and the result shows a D (ferrocene)-π-A (BODIPY) system. The energy gap between the HOMO and LUMO had a good consistence with the electrochemical experiment and UV-vis data. The calculation of the frontier orbital belonging to the cation state of DiFc-B shows the directional change of the D-π-A system, which supplied a theoretical basis of the electrochromism.     

Unraveling pharmaceuticals removal in a sulfur-driven autotrophic denitrification process: Performance,kinetics and mechanisms

The removal of eight typical pharmaceuticals (PhACs) (i.e., ibuprofen (IBU), ketoprofen (KET), diclofenac (DIC), sulfadiazine (SD), sulfamethoxazole (SMX), trimethoprim (TMP), ciprofloxacin (CIP) and enoxacin (ENO)) in sulfur-driven autotrophic denitrification (SdAD) process were firstly investigated via long-term operation of bioreactor coupled with batch tests. The results indicated that IBU and KET can be effectively removed (removal efficiency > 50%) compared to other six PhACs in SdAD bioreactor. Biodegradation was the primary removal route for IBU and KET with the specific biodegradation rates of 5.3±0.7～18.1±1.8 µg g^?1-VSS d^?1 at initial concentrations of 25-200 µg/L. The biotransformation intermediates of IBU and KET were examined, and the results indicated that IBU was biotransformed to three intermediates via hydroxylation and carboxylation. KET biotransformation could be initiated from the reduction of the keto group following with a series of oxidation/reduction reactions, and five intermediates of KET were observed in this study. The microbial community composition in the system was markedly shifted when long-term exposure to PhACs. However, the functional microbes (e.g., genus Thiobacillus) showed high tolerance to PhACs, resulting in the high efficiency for PhACs, N and S removal during long-term SdAD reactor operation. The findings provide better insight into PhACs removal in SdAD process, especially IBU and KET, and open up an innovative opportunity for the treatment of PhACs-laden wastewater using sulfur-mediated biological process.     

Boranil dyes bearing tetraphenylethene: Synthesis,AIE/AIEE effect properties,pH sensitive properties and application in live cell imaging

A serial of novel fluorescent boranil dyes (7, 8, 9, 10) bearing tetraphenylethene were prepared through an efficient process. These dyes exhibited large stokes shifts (more than 5000?cm^?1) and moderate fluorescent quantum yield from 0.22–0.53. Dye 9 exhibited AIE/AIEE and exhibited weak fluorescence in pure MeCN or the MeCN/water mixture with a water fraction below 80%, in which a significant AIEE effect was observed in the mixture with 80% of water fraction and a sharp increasement in fluorescence intensity was also observed. And dye 8 and 10 showed moderate solvatochromism with the solvent changed from toluene to DMSO, and they displayed sensitivities to pH change in MeCN/water solution. Interestingly, dyes 8 and 10 obtained by column chromatography and slow solvent evaporation showed different X-ray diffraction properties. Moreover, compound 8 and 10 could be applied to cell imaging.     

Solubility of small molecule in ionic liquids: a model study on the ionic size effect

Recently, the solvent power of ionic liquid (IL) has been described based on Flory-Huggins (FH) theory assuming that the volumes of the components are the same (J. Phys. Chem. B, 2006, 110, 16205). Here, we extended the FH theory to derive the solvent power in the case of different sizes (molar volumes) of the IL's components based on "polymer-like" model. Applying this model, the effect of ionic size on the solvent power of ionic liquids has been investigated. It was found that the effect of size can be characterized by introducing the effective volume (V+ and V-) of each site of the ion, and for the equivalent ionic liquid, the larger effective volume of the ionic liquid has the larger solvent power. Our results are in excellent agreement with the experimental solubility data in various ionic liquids.     

Simulating the formation of sodium:electron tight-contact pairs: watching the solvation of atoms in liquids one molecule at a time

The motions of solvent molecules during a chemical transformation often dictate both the dynamics and the outcome of solution-phase reactions. However, a microscopic picture of solvation dynamics is often obscured by the concerted motions of numerous solvent molecules that make up a condensed-phase environment. In this study, we use mixed quantum/classical molecular dynamics simulations to furnish the molecular details of the solvation dynamics that leads to the formation of a sodium cation-solvated electron contact pair, (Na(+), e(-)), in liquid tetrahydrofuran following electron photodetachment from sodide (Na(-)). Our simulations reveal that the dominant solvent response is comprised of a series of discrete solvent molecular events that work sequentially to build up a shell of coordinating THF oxygen sites around the sodium cation end of the contact pair. With the solvent response described in terms of the sequential motion of single molecules, we are then able to compare the calculated transient absorption spectroscopy of the sodium species to experiment, providing a clear microscopic interpretation of ultrafast pump-probe experiments on this system. Our findings suggest that for solute-solvent interactions similar to the ones present in our study, the solvation dynamics is best understood as a series of kinetic events consisting of reactions between chemically distinct local structures in which key solvent molecules must be considered to be part of the identity of the reacting species.     

Late stage of the phase-separation process: coalescence-induced coalescence, gravitational sedimentation, and collective evaporation mechanisms

We study the separation in the binary and ternary mixtures of the water/surfactant C12E5/polymer PEG system. The phase separation in the mixtures at late stages is governed by two distinct mechanisms: the coalescence-induced coalescence and the droplet evaporation mechanism. We show that when the coalescence-induced coalescence process is globally terminated in the sample consisting of a dense system of domains, another mechanism, which we call the collective droplet evaporation, starts to dominate. It manifests itself as a front of "evaporating" domains, which propagates at constant speed in the system. We show that the collective evaporation is induced by the gravitational drift of large droplets.     

Dependence of charge-transport parameters on static correlation and self-interaction energy: the case of a 1,4-bis(phenylethynyl)benzene derivative conjugated molecule

The current research on molecular-based devices built with highly unsaturated molecules is largely assisted by computational techniques. These modern computational tools are intended to serve (i) to understand the relation between the mechanism of charge transport and the chemical composition of the semiconductors and (ii) to perform the molecular engineering needed to design new and more efficient organic materials. We have studied the case of a rod-shaped conjugated molecule widely used in molecular electronics. The results of multireference perturbation theory up to second order (MRMP2) and complete active space self-consistent field calculations (CASSCF) are compared with the results provided by energy density functionals. Motivated by the diverse accuracy of the results depending on the theoretical method selected, we have systematically studied the physical origin of the discrepancies. We find that a subtle interplay between correlation effects and the self-interaction energy mainly governs the results, which makes it thus difficult to anticipate the quality of a method without knowing in advance its dependence on both effects. We thus encourage careful testing of computational methods for the rational design and understanding of conjugated materials for charge conduits.     

The effect of diphenylamine on the electronic, optical, and charge transport properties of BTD-based derivative: Insights from theory

Theoretical investigations have been performed to explore the variation in electronic,optical,and charge transport properties upon the change of the chemical composition along the backbone in 2,1,3-benzothiadiazole(BTD)-based derivative.Narrow difference between hole and electron transportations with the charge hopping model indicates studied BTD-based derivative can be used as good ambipolar transport material in organic light-emitting diodes.     

The effect of scoparone, a coumarin derivative isolated from the Chinese crude drug Artemisiae capillaris flos, on the heart

In the present study, scoparone isolated from Artemisia Capillaris Flos has been investigated to determine its pharmacological properties on the heart. Scoparone was found to cause the increase in coronary flow and heart rate, but did not affect cardiac output, left ventricular pressure or left ventricular work in the isolated perfused heart. Scoparone at 25 mg/kg and 50 mg/kg, p.o. had a marked inhibitory effect on the ST wave depression. Consequently it is suggested that scoparone has antianginal action.     

Phosphated polyurethane dispersions: synthesis,emulsification mechanisms and the effect of the neutralising base

Phosphate-containing polyester macroglycols with different phosphate contents were synthesised from a phosphorus-containing monomer, a dicarboxylic acid and a diol. The macroglycols were then used as a soft segment for the preparation of segmented polyurethane dispersions. Aqueous dispersions were made by phase inversion from the organic solvent after the carboxylic acid groups were neutralized. Phase inversion was found to take place in three distinct stages. The stability and particle size of the polyurethane dispersions were dependent of the amount of carboxylic acid groups present, the degree of neutralisation and the neutralising cations. Metal-neutralized polyurethane dispersions gave smaller particle sizes and the corresponding films showed higher swelling in water due to the ease of hydration. The particle size and stability of the tertiary amine-neutralised polyurethanes were found to be related to the water solubility of the amines at a given dispersion temperature. Particle size increases for the higher alkyl chain neutalising amines due to the poor hydration of the corresponding cations.     

A new insight into encapsulation process of a drug molecule in the polymer/surfactant system: a molecular simulation study

Structural Chemistry - Drug delivery plays a substantial role in a more effective treatment of diseases of the central nervous system; therefore, the selection of an appropriate drug carrier system...     

Isolated monohydrates of a model peptide chain: effect of a first water molecule on the secondary structure of a capped phenylalanine

The formation of monohydrates of capped phenylalanine model peptides, CH(3)-CO-Phe-NH(2) and CH(3)-CO-Phe-NH-CH(3), in a supersonic expansion has been investigated using laser spectroscopy and quantum chemistry methods. Conformational distributions of the monohydrates have been revealed by IR/UV double-resonance spectroscopy and their structures assigned by comparison with DFT-D calculations. A careful analysis of the final hydrate distribution together with a detailed theoretical investigation of the potential energy surface of the monohydrates demonstrates that solvation occurs from the conformational distribution of the isolated peptide monomers. The distribution of the monohydrates appears to be strongly dependent on both the initial monomer conformation (extended or folded backbone) and the solvation site initially occupied by the water molecule. The solvation processes taking place during the cooling can be categorized as follows: (a) solvation without significant structural changes of the peptide, (b) solvation inducing significant distortions of the backbone but retaining the secondary structure, and (c) solvation triggering backbone isomerizations, leading to a modification of the peptide secondary structure. It is observed that solvation by a single water molecule can fold a β-strand into a γ-turn structure (type c) or induce a significant opening of a γ-turn characterized by an elongated C(7) hydrogen bond (type b). These structural changes can be considered as a first step toward the polyproline II condensed-phase structure, illustrating the role played by the very first water molecule in the solvation process.     

Remarks on the concept of an atom in a molecule and on charge transfer between atoms on molecule formation

Density functional theory provides a natural and rigorous definition of an atom in a molecule in its ground state: The molecular electron density is the sum of atomic densities, the atoms have the same chemical potential as does the molecule, and the atoms are minimally promoted from their ground states. These atoms in general are not spherical, and in general they bear nonintegral charges. Charge transfer on molecule formation is thereby uniquely defined. Calculations by Palke and by Guse are reviewed, in which the hydrogen atom is identified in the hydrogen molecule.