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Graphene is a material with outstanding properties and numerous potential applications in a wide range of research and technology areas, spanning from electronics, energy materials, sensors, and actuators to life-science and many more. However, the insolubility and poor dispersibility of graphene are two major problems hampering its use in certain applications. Tethering mono-, di-, or even poly-saccharides on graphene through click-chemistry is gaining more and more attention as a key modification approach leading to new graphene-based materials (GBM) with improved hydrophilicity and substantial dispersibility in polar solvents, e.g., water. The attachment of (poly)saccharides on graphene further renders the final GBMs biocompatible and could open new routes to novel biomedical and environmental applications. In this review, recent modifications of graphene and other carbon rich materials (CRMs) through click chemistry are reviewed.

In this work three molecules exhibiting dual sensing solvatochromic behaviors are examined in the context of solvation in binary solvent mixtures (BSMs). The compounds studied involve two functional groups with high responsiveness to solvent polarity namely pentacyanoferrate(II) (PC) and azo groups. Two of these compounds are [2]rotaxanes involving alpha- or beta- cyclodextrin (CyD) and the third is their CyD-free precursor. The dual solvatochromic behavior of these compounds is investigated in water/ethlylene glycol (EG) mixtures and their dual solvatochromic responses are assessed in terms of the intensity of solvatochromism and the extent of preferential solvation. To achieve this the linear solvation model by Kamlet, Abboud and Taft [J. Organomet. Chem. 1983, 48, 2877–2887] and the two-phase model of solvation by Bagchi and coworkers [J. Phys. Chem. 1991, 95, 3311–3314] are employed. The influence of the presence or lack of CyD (alpha- or beta-) on these dual solvatochromic sensors is analyzed.

Graphene has stimulated great enthusiasm in a variety of fields, while its chemically inert surface still remains challenging for functionalization towards various applications. Herein, we report an approach to fabricate non-covalently functionalized graphene by employing pi-pi stacking interactions, which has potentialities for enhanced ammonia detection. 5,5 '-Di(4-biphenylyl)-2,2 '-bithiophene (BP2T) molecules are used in our work for the non-covalent functionalization through strong pi-pi interactions of aromatic structures with graphene, and systematic investigations by employing various spectroscopic and microscopic characterization methods confirm the successful non-covalent attachment of the BP2T on the top of graphene. From our gas sensing experiments, the BP2T functionalized graphene is promising for ammonia sensing with a 3-fold higher sensitivity comparing to that of the pristine graphene, which is mainly attributed to the enhanced binding energy between the ammonia and BP2T molecules derived by employing the Langmuir isotherm model. This work provides essential evidence of the pi-pi stacking interactions between graphene and aromatic molecules, and the reported approach also has the potential to be widely employed in a variety of graphene functionalizations for chemical detection. Hu Li and Tianbo Duan share first authorship

In this work we utilize the marked solvatochromism of two cyclodextrin (CD) containing [2]rotaxanes and their CD-free linear precursor in order to investigate preferential solvation (PS) effects in water/ethylene glycol mixtures. Two well-known models of PS are employed in order to quantify the PS and rationalize local solute-solvent and solvent-solvent effects. Structural effects among the solvatochromic probes are furthermore examined in terms of the involvement or not of a CD macrocycle and also in terms of the size of CD involved, between the two [2]rotaxanes.

International audience; Water oxidation by copper-based complexes to form dioxygen has attracted attention in recent years, with the aim of developing efficient and cheap catalysts for chemical energy storage. In addition, high-valent metal–oxo species produced by the oxidation of metal complexes in the presence of water can be used to achieve substrate oxygenation with the use of H2O as an oxygen source. To date, this strategy has not been reported for copper complexes. Herein, a copper(II) complex, [(RPY2)Cu(OTf)2] (RPY2=N-substituted bis[2-pyridyl(ethylamine)] ligands; R=indane; OTf=triflate), is used. This complex, which contains an oxidizable substrate moiety (indane), is used as a tool to monitor an intramolecular oxygen atom transfer reaction. Electrochemical properties were investigated and, upon electrolysis at 1.30 V versus a normal hydrogen electrode (NHE), both dioxygen production and oxygenation of the indane moiety were observed. The ligand was oxidized in a highly diastereoselective manner, which indicated that the observed reactivity was mediated by metal-centered reactive species. The pH dependence of the reactivity was monitored and correlated with speciation deduced from different techniques, ranging from potentiometric titrations to spectroscopic studies and DFT calculations. Water oxidation for dioxygen production occurs at neutral pH and is probably mediated by the oxidation of a mononuclear copper(II) precursor. It is achieved with a rather low overpotential (280 mV at pH 7), although with limited efficiency. On the other hand, oxygenation is maximum at pH 8–8.5 and is probably mediated by the electrochemical oxidation of an antiferromagnetically coupled dinuclear bis(μ-hydroxo) copper(II) precursor. This constitutes the first example of copper-centered oxidative water activation for a selective oxygenation reaction.

The impact of solvent basicity on the solvatochromism of pentacyanoferrate(II) complexes has scarcely been discussed. In this work a study of the influence of solvent basicity on the local effects occurring in binary solvent mixtures consisting of an amide and water or an alcohol and water is reported. The author argues that the reason of the underestimation of the impact of solvent basicity on the solvatochromism of pentacyanoferrate(II) complexes is the use of empirical indicator-centric solvent basicity parameters for the description of solvatochromic shifts. The model of Inomata and coworkers [J. Phys. Chem. B 119 (2015) 14738–14,749] was utilized as a means to determine local, solute-centric basicity in three cases of binary solvent mixtures involving a pentacyanoferrate(II) complex as s'olute. Solute- and indicator-centric excess basicities were compared. It was found that the solute-centric properties markedly differed from the corresponding published indicator-centric properties. The contribution of the basicity was determined for each case of solvent mixture with the use of suitable linear solvation energy relationships (LSERs) involving terms expressing Lewis acidity, dipolarity, and the basicity of the medium. Additionally, a modified Redlich–Kister (CNIBS/R–K) equation, was employed for the algebraic description of the solute-centric solvent polarity parameters.

The cyclopropyl (cPr) group, which is a well-known probe for detecting radical character at atoms to which it is connected, is tested as an indicator for aromaticity in the first ππ* triplet and singlet excited states (T1 and S1 ). Baird's rule says that the π-electron counts for aromaticity and antiaromaticity in the T1 and S1 states are opposite to Huckel's rule in the ground state (S0 ). Our hypothesis is that the cPr group, as a result of Baird's rule, will remain closed when attached to an excited-state aromatic ring, enabling it to be used as an indicator to distinguish excited-state aromatic rings from excited-state antiaromatic and nonaromatic rings. Quantum chemical calculations and photoreactivity experiments support our hypothesis; calculated aromaticity indices reveal that openings of cPr substituents on [4n]annulenes ruin the excited-state aromaticity in energetically unfavorable processes. Yet, polycyclic compounds influenced by excited-state aromaticity (e.g., biphenylene), as well as 4nπ-electron heterocycles with two or more heteroatoms represent limitations.

Mono- and di-quaternized 4,4′-bipyridine derivatives constitute a family of heterocyclic compounds, which in recent years have been employed in numerous applications. These applications correspond to various disciplines of research and technology. In their majority, two key features of these 4,4′-bipyridine-based derivatives are exploited: their redox activity and their electrochromic aptitude. Contemporary materials and compounds encompassing these skeletons as building blocks are often characterized as multifunctional, as their presence often gives rise to interesting phenomena, e.g., various types of chromism. This research trend is acknowledged, and, in this review article, recent examples of multifunctional chromic materials/compounds of this class are presented. Emphasis is placed on solvent-/medium- and environment-responsive 4,4′-bipyridine derivatives. Two important classes of 4,4′-bipyridine-based products with solvatochromic and/or environment-responsive character are reviewed: viologens (i.e., N,N′-disubstituted derivatives) and monoquats (i.e., monosubstituted 4,4′-bipyridine derivatives). The multifunctional nature of these derivatives is analyzed and structure–property relations are discussed in connection to the role of these derivatives in various novel applications.

In this work we report the synthesis of two fluorescent 2-pyrazoline derivatives exhibiting remarkable (fluoro)solvatochromic behavior. The pyrazolines were synthesized in one step from the corresponding monocarbonyl curcuminoids and 4-hydrazinobenzoic acid in high yield and purity and were fully characterized by means of NMR and FT-IR spectroscopy and HRMS spectrometry. The structure of the novel derivative 2 was also characterized by means of X-ray crystallography. Both compounds were studied computationally in the gas phase. Additionally, the effects of solvent polarity on the absorption and fluorescence spectra of these derivatives were investigated in a solvent group consisting of various neat molecular solvents exhibiting hydrogen bond donating (HBD), hydrogen bond accepting (HBA), and/or dipolar behavior. The solvent effects observed were quantified and rationalized by employing suitable multiparametric Linear Solvation Energy Relationships (LSERs) involving dipolarity, HBD-acidity and HBA-basicity terms. The contribution of each of these parameters provided insights on the predominant solute-solvent interactions occurring in solution. Importantly, some differences in the (fluoro)solvatochromic aptitude/behavior were revealed among the derivatives and they were rationalized on the basis of their structural diversity.

In this work, the preferential solvation of an intensely solvatochromic ferrocyanide(II) dye involving a 4,4'-bipyridine-based ligand was examined in various binary solvent mixtures. Its solvatochromic behavior was rationalized in terms of specific and nonspecific solute-solvent interactions. An exceptional case of solvatochromic inversion was observed when going from alcohol/water to amide/water mixtures. These effects were quantified using Onsager's solvent polarity function. Furthermore, the sensitivity of the solvatochromism of the dye was determined using various solvatochromic parameters such as π* expressing the dipolarity/polarizability of solvents and α expressing the hydrogen-bond-donor acidity of solvents. This analysis was useful for the rationalization of the selective solvation phenomena occurring in the three types of alcohol/water and amide/water mixtures studied. Furthermore, two preferential solvation models were employed for the interpretation of the experimental spectral results in binary solvent mixtures, namely, the model of Suppan on dielectric enrichment [J. Chem. Soc. Faraday Trans. 1 1987, 83, 495-509] and the model of Bosch, Rosés, and co-workers [J. Chem. Soc., Perkin Trans. 2, 1995, 8, 1607-1615]. The first model successfully predicted the charge transfer energies of the dye in formamide/water and N-methylformamide/water mixtures, but in the case of MeOH/water mixtures, the prediction was less accurate because of the significant contribution of specific solute-solvent interactions in that case. The second model gave more insights for both specific solute-solvent as well as solvent-solvent interactions in the cybotactic region. The role of dielectric enrichment and specific interactions was discussed based on the findings.

We have investigated spectrally, crystallographically as well as computationally the charge transfer complexes involving newly synthesized N-aryl-N′-methyl non-symmetric viologens (AMVs) and hexacyanoferrate(II) (HCF) anions. The supramolecular binding of AMVs and HCF was studied in solution and in the crystal state for one of the obtained complexes. Substituent effects on the electron affinities of the dicationic AMVs, determined using Mulliken's theory [R. S. Mulliken, J. Am. Chem. Soc., 1952, 74, 811–824] were quantified. The structure of one of the AMV//FeII(CN)6 pairs solved through Single-Crystal X-ray Diffraction (SCXRD), provided insights for the supramolecular binding of the anionic and cationic counterparts and the role of lattice water molecules. Supramolecular binding in solution, studied with the use of NMR spectroscopy, is in agreement with the results obtained in the solid state.

The solvatochromic behavior of novel synthesized azo-containing viologen-based rotaxanes, combining push–pull linear and α or β-cyclodextrin macrocyclic components is examined. These rotaxanes are stoppered by pentacyanoferrate(II) units. The latter stabilize these systems and furthermore act as strong electron donors. These units are linked to strong electron withdrawing viologen units thus giving rise to an exceptionally intense solvatochromic behavior. Suitable solvent polarity scales and Linear Solvation Energy Relationships (LSERs) were employed in order to rationalize the solvent polarity effects observed, both specific and non-specific ones. The results for the title compounds as well as their Cyclodextrin-Free-Dumbbell (CFD) like analogue, are compared to recent published solvatochromic data regarding similar smaller pentacyanoferrate(II) complexes as well as other highly solvatochromic compounds. Structural effects on the solvatochromic intensity as well as the contribution of different solvent-solute interactions are rationalized and quantified.

The antiaromatic character of benzene in its first ππ* excited triplet state (T1) was deduced more than four decades ago by Baird using perturbation molecular orbital (PMO) theory [J. Am. Chem. Soc. 1972, 94, 4941], and since then it has been confirmed through a range of high-level quantum chemical calculations. With focus on benzene we now first review theoretical and computational studies that examine and confirm Baird's rule on reversal in the electron count for aromaticity and antiaromaticity of annulenes in their lowest triplet states as compared to Hückel's rule for the ground state (S0). We also note that the rule according to quantum chemical calculations can be extended to the lowest singlet excited state (S1) of benzene. Importantly, Baird, as well as Aihara [Bull. Chem. Soc. Jpn. 1978, 51, 1788], early put forth that the destabilization and excited state antiaromaticity of the benzene ring should be reflected in its photochemical reactivity, yet, today these conclusions are often overlooked. Thus, in the second part of the article we review photochemical reactions of a series of benzene derivatives that to various extents should stem from the excited state antiaromatic character of the benzene ring. We argue that benzene can be viewed as a molecular "Dr Jekyll and Mr Hyde" with its largely unknown excited state antiaromaticity representing its "Mr Hyde" character. The recognition of the "Jekyll and Hyde" split personality feature of the benzene ring can likely be useful in a range of different areas.

A new solvatochromic pentacyanoferrate(II) complex with a 4,4′-bipyridine based dicationic ligand was synthesized and characterized. Its chromotropic behavior markedly affected by solvent polarity was examined in different media i.e. neat solvents, binary solvent mixtures, and aqueous glucose solutions, and quantified using suitable solvent polarity parameters. The metal to ligand charge transfer (MLCT) energy shows a linear correlation with the Reichardt solvent polarity parameter as well as the Kirkwood dipolarity function and suitable functions expressing polarizability. Using suitable Linear Solvation Energy Relationships (LSERs) it was concluded that mainly specific solute–solvent interactions contribute to the solvatochromic phenomenon. The investigation of the solvatochromic behavior of the title compound in aqueous glucose solutions revealed a different response to medium polarity. Tuning of the solvatochromic intensity of the title compound by changing the type of medium was further studied focusing on aqueous glucose solutions.

The first hydrogenation step of benzene, which is endergonic in the electronic ground state (S0), becomes exergonic in the first triplet state (T1). This is in line with Baird's rule, which tells that benzene is antiaromatic and destabilized in its T1 state and also in its first singlet excited state (S1), opposite to S0, where it is aromatic and remarkably unreactive. Here we utilized this feature to show that benzene and several polycyclic aromatic hydrocarbons (PAHs) to various extents undergo metal-free photochemical (hydro)silylations and transfer-hydrogenations at mild conditions, with the highest yield for naphthalene (photosilylation: 21%). Quantum chemical computations reveal that T1-state benzene is excellent at H-atom abstraction, while cyclooctatetraene, aromatic in the T1 and S1 states according to Baird's rule, is unreactive. Remarkably, also CVD-graphene on SiO2 is efficiently transfer-photohydrogenated using formic acid/water mixtures together with white light or solar irradiation under metal-free conditions., Baird's rules say that the first triplet state of benzene displays antiaromatic character. Here, the authors exploit this to show that aromatic molecules can undergo rapid transfer hydrogenation or silylations without the need for metal catalysts when photochemcially excited into this state.

A group of new non-symmetric viologens was synthesized and characterized spectrally using various techniques. These viologens contain active methylene moieties being capable to act as hydrogen bond donors (HBD) and interact in solution with various solvents, the latter acting as hydrogen bond acceptors (HBA). These specific solute-solvent interactions result in intense coloration of the resulting solutions. The chromotropic behavior of these compounds is triggered by basic solvents, and no significant change in color is observed in poorer HBA-solvents, such as several alcohols. The dependence of the color of the solutions on the polarity parameters of solvents (solvatochromism) was investigated. Solvent polarity parameters expressing both dipolarity/polarizability and basicity of solvents have been used. Finally the correlation of the chromotropic behavior of these compounds with their structure is examined, using both experimental data and Hammett equation.

In this work, a new [2]rotaxane consisted of a diazobenzene containing π-conjugated linear compartment, including the 4,4′-bipyridyl moiety and α-cyclodextrin (α-CD) as the macrocyclic compartment, was synthesised with yields of nearly 57% and fully characterised. α-CD easily assembled with the linear compartment and suitable bulky ends (stoppers) in water to give a new [2]rotaxane. The characterisation of this supramolecular compound was accomplished using several spectroscopic techniques such as 1H NMR, 13C NMR and 2D NMR spectroscopy, powder X-ray diffraction, fourier transform infrared spectroscopy, induced circular dichroism and UV–vis spectrophotometry, as well as scanning electron microscopy and Energy Dispersive X-ray. Furthermore, the reversible E–Z photoisomerisation of both [2]rotaxane and its molecular dumbbell was investigated by irradiation with UV light.

The intense solvatochromic behavior of several pentacyanoferrate complexes with aryl substituted 4,4′-bipyridines acting as ligands, was investigated in six hydroxylic and non hydroxylic solvents using UV-Visible spectroscopy. The metal-to-ligand-charge-transfer bands of the visible spectra of these compounds proved to be markedly affected by solvent polarity. In order to quantify the extent of the observed solvatochromism and reveal the dominant interactions which take place in the cybotactic region, resulting in solvatochromism, the Kamlet-Taft equation was used. This is a multiparametric linear-solvation-energy-relationship (LSER) widely used for the study of solvent effects on various physicochemical properties. Through this analysis it was proved that both specific and non specific interactions contribute to the observed solvatochromism. Furthermore, the preferential solvation of the complex salts was studied in binary solvent mixtures. Solvatochromism was used as the key approach to rationalize solvent-solute and solvent-solvent interactions in the binary solvent mixtures studied.

In this work six new 4-aryl substituted bispyridinium salts have been synthesized using 2,4-dinitrophenyl- bispyridinium chloride as the starting material, which was arenamine exchanged via the Zincke reaction. These aromatic heterocyclic salts were used as ligands, acting as Lewis bases to form a series of 4-pentacyanoferrate-4′-aryl substituted bispyridinium complex salts in high yields. The complex salts were characterized using several spectroscopic techniques including 1H as well as 13C NMR spectroscopy, UV–Vis and FTIR spectrophotometry. These materials present a number of interesting electronic and optical properties. Herein we mainly focused on the electronic absorption of these materials. The visible metal-to-ligand-charge-transfer (MLCT) band of these materials assigned as dπ(FeII) π*(L) was proved to be affected by substituent changes (of the benzene ring of the complexes) but mainly by solvent polarity changes. Band shifts of even 4000 cm−1 were induced by small solvent polarity changes (e.g., water to methanol). The Vis absorption spectra were investigated in four protic solvents (water, 2,2,2-trifluoroethanol, ethylene glycol, and methanol). The substituent effects were then quantified using the Hammett equation which correlates the MLCT absorption wavenumbers with the Hammett constant (σx). Furthermore, two of the most successful solvent polarity parameters (the acceptor number AN and the normalized solvent polarity scale E) were used to quantify the solvent polarity effects on the MLCT absorption wavenumbers. The correlations obtained in all cases proved to be satisfactory. The dominant interaction responsible for the solvent polarity effects proved to be the hydrogen-bond formation between the cyano groups of the complex salts and the protic solvents. Copyright © 2009 John Wiley & Sons, Ltd.

Herein, a photochemical method for functionalization of graphene using 2-propanol is reported. The functionalization method which is catalyst-free operates at ambient temperature in neat 2-propanol ...

A novel tetranuclear copper(II) complex (1) was synthesized from the self-assembly of copper(II) perchlorate and the ligand N-benzyl-1-(2-pyridyl)methaneimine (L(1)). Single-crystal X-ray diffraction studies revealed that complex 1 consists of a Cu4(OH)4 cubane core, where the four copper(II) centers are linked by μ3-hydroxo bridges. Each copper(II) ion is in a distorted square-pyramidal geometry. X-ray analysis also evidenced an unusual metal cation-π interaction between the copper ions and phenyl substituents of the ligand. Calculations based on the density functional theory method were used to quantify the strength of this metal-π interaction, which appears as an important stabilizing parameter of the cubane core, possibly acting as a driving parameter in the self-aggregation process. In contrast, using the ligand N-phenethyl-1-(2-pyridyl)methaneimine (L(2)), which only differs from L(1) by one methylene group, the same synthetic procedure led to a binuclear bis(μ-hydroxo)copper(II) complex (2) displaying intermolecular π-π interactions or, by a slight variation of the experimental conditions, to a mononuclear complex (3). These complexes were studied by X-ray diffraction techniques. The magnetic properties of complexes 1 and 2 are reported and discussed.

This work deals with the design, synthesis, and characterization of a new solvatochromic dye. The intense solvatochromic behavior of this new synthesized non symmetric viologen was investigated using UV–Vis spectrophotometry. A further purpose was the study of the interactions between the solvent and solute molecules responsible for the solvatochromism. Several protic and aprotic solvents were used, and the resulting absorption maxima wavenumbers obtained via UV–Vis spectrophotometry, were correlated with the solvent polarity parameters, E T (30) (Dimroth–Reichardt solvent polarity parameter) and the Gutmann’s donor number (DN) using the biparametric model introduced by Krygowski and Fawcett. The analysis of the relative contribution of each parameter has clearly shown that the dominating interaction responsible for the solvatochromic behavior observed is the proton donation by the solute molecules to the solvent molecules, the latter acting as a Lewis bases. This is an interaction which can be described by DN. Additionally, the good correlation with the Kamlet–Taft parameter β is in good agreement.

The photoconductive properties of an azo-containing [2]rotaxane, bearing a π-conjugated axial part and its corresponding dumbbell compound are investigated. Structural effects on the observed photoconductive behavior in both cases are discussed. The photoresponsive behavior of the title [2]rotaxane was proved to be more intense than that of its analogue lacking the α-cyclodextrin (α-CyD) macrocycle. A mechanism of the photoinduced charge transport in both cases is proposed.