Advanced Functional Luminescent Metallomesogens: The Key Role of the Metal Center

The use of liquid crystals for the fabrication of displays incorporated in technological devices (TVs, calculators, screens of eBook's, tablets, watches) demonstrates the relevance that these materials have had in our way of living. However, society evolves, and improved devices are looked for as we create a more efficient and safe technology. In this context, metallomesogens can behave as multifunctional materials because they can combine the fluidic state of the mesophases with properties such as photo and electroluminescence, which offers new exciting possibilities in the field of optoelectronics, energy, environment, and even biomedicine. Herein, it has been established the role of the molecular geometry induced by the metal center in metallomesogens to achieve the self-assembly required in the liquid-crystalline mesophase. Likewise, the effect of the coordination environment in metallomesogens has been further analyzed because of its importance to induce mesomorphism. The structural analysis has been combined with an in-depth discussion of the properties of these materials, including their current and potential future applications. This review will provide a solid background to stimulate the development of novel and attractive metallomesogens that allow designing improved optoelectronic and microelectronic components. Additionally, nanoscience and nanotechnology could be used as a tool to approach the design of nanosystems based on luminescent metallomesogens for use in bioimaging or drug delivery.

A novel biphenyl-derived salicylhydrazone Schiff base fluorescent probes for identification of Cu2+ and application in living cells

A novel biphenyl-derived salicylhydrazone Schiff base (BSS) fluorescent probes for highly sensitive and selective identification of Cu²⁺ has been synthesized. In addition, the recognition has been proved experimentally. The results indicated that the complex forms a 1:1 complex with Cu²⁺ shows fluorescent quenching. Furthermore, the detection limit of 1.54×10^-8M. More interesting, the probe BSS not only have a good biocompatibility in living cells, but also the sense behavior of Cu²⁺ in the cell nucleus.

Supramolecular Aggregation of a New Substituted Bis(salicylaldiminato)zinc(II) Schiff-Base Complex Derived from trans-1,2-Diaminocyclohexane

In this contribution is reported the synthesis, characterization, and aggregation properties in solution of a novel Zn(II) complex, (R)-2, derived from the enantiopure chiral trans-1,2-diaminocyclohexane and a substituted salicylaldehyde. Detailed 1H NMR, DOSY NMR, optical absorption, and circular dichroism spectroscopic studies and chemical evidence allowed to investigate the nature of aggregate species in solution. The high solubility of (R)-2 in solution of the non-coordinating chloroform solvent leads to formation of various aggregates, some of them consisting of large oligomers estimated to contain up to 27 monomeric units. The chiral trans-stereochemistry of the bridging diamine favors a different aggregation mode in these complexes, both in the oligomers and dimers, involving a tetrahedral coordination geometry around the metal center. Overall data suggest the formation of helical oligomers, (ZnL)n, in freshly prepared chloroform solutions which, by standing or heating, evolve towards a more thermodynamically stable, dinuclear double-helicate Zn2L2 dimer.

Vapochromic and chemiresistive characteristics of a nanostructured molecular material composed of a zinc(ii)-salophen complex

A Zn^II Schiff-base complex shows vapochromic and chemiresistive behaviour when exposed to vapours of a Lewis base.

A novel, highly sensitive, selective, reversible and turn-on chemi-sensor based on Schiff base for rapid detection of Cu(II)

In this work, a novel optical fluoro-chemisensor was designed and synthesized for copper (II) ions detection. The sensor film is created by embedded N,N-Bis(2-hydroxo-5-bromobenzyl)ethylenediamine in poly vinyl chloride (PVC) film in presence of dioctyl phthalate (DOP) as plasticizer. The receptor Schiff base reveals "off-on" mode with high selectivity, significant sensitivity to Cu(II) ions. The selectivity of optical sensor for Cu(II) ions is the result of chelation enhanced fluorescence (CHEF). The optimal conditions of pH and response time at which higher efficiency of sensor film is performed was found to be 6.8 and 2.48min. The possible interference of other metal ions in solution was examined in presence of different types of metal ions. This film shows high selectivity and ultra-sensitivity with low detection limit LOD (1.1×10^-8M). Thus, these considerable properties make it viable to monitor copper metal ions within very low concentration range (0-15×10^-6M Cu(II)) and highly selective even in the presence of different types of metal ions. The sensor reversibility was achieved by utilizing EDTA solution with concentration of 0.1M solution.

Benzophenone based fluorophore for selective detection of Sn2+ ion: Experimental and theoretical study

Synthesis of novel benzophenone-based chemosensor is presented for the selective sensing of Sn²⁺ ion. Screening of competitive metal ions was performed by competitive experiments. The specific cation recognition ability of chemosensor towards Sn²⁺ was investigated by experimental (UV-visible, fluorescence spectroscopy, ¹H NMR, ¹³C NMR, FTIR and HRMS) methods and further supported by Density Functional Theory study. The stoichiometric binding ratio and binding constant (K_a) for complex is found to be 1:1 and 1.50×10⁴, respectively. The detection limit of Sn²⁺ towards chemosensor was found to be 0.3898ppb. Specific selectivity and superiority of chemosensor over another recently reported chemosensor is presented.

New phosphorescent platinum(ii) complexes with tetradentate C*N^N*C ligands: liquid crystallinity and polarized emission

Novel tetradentate cyclometalated platinum(ii) complexes bearing two peripheral alkoxy chains can self-assemble into thermotropic smectic liquid crystalline complexes and show a polarized emission.

On the Lewis acidic character of bis(salicylaldiminato)zinc(ii) Schiff-base complexes: a computational and experimental investigation on a series of compounds varying the bridging diimine

The electronic effects induced by the geometry of the 1,2-diimine bridge control the Lewis acidic character in a series of Zn^II Shiff-base complexes.

A highly selective, sensitive and reversible fluorescence chemosensor for Zn2+ and its cell viability

A new ligand (H2L) was synthesized and designed for sensing properties. H2L shows fluorescence ‘switch ON’ with Zn²⁺ ions with a detection limit of 1.47 μM. The H2L and 1 showed marginal toxicity against MCF-7 and A375 cell lines.

Synthesis and characterization of a novel, ditopic, reversible and highly selective, “Turn-On” fluorescent chemosensor for Al3+ ion

A ditopic Schiff base fluorescent chemosensor, L (OFF state), selectively senses Al³⁺ by inhibition of ESIPT/GSIPT, CN isomerization and CHEF (ON state).

Synthesis and aggregation behaviour of luminescent mesomorphic zinc(ii) complexes with ‘salen’ type asymmetric Schiff base ligands

Mesomorphism and solvent dependent aggregation behaviour of a new series of photoluminescent Zn(ii)-salen type asymmetric Schiff base complexes have been investigated.

A cap-type Schiff base acting as a fluorescence sensor for zinc(II) and a colorimetric sensor for iron(II), copper(II), and zinc(II) in aqueous media

A simple and low cost chemosensor is described. This sensor could simultaneously detect three biologically important metal ions through fluorogenic (Zn(2+)) and chromogenic (Fe(2+), Cu(2+), and Zn(2+)) methods in aqueous solution. The sensor could function as a "turn-on" fluorescence receptor only to Zn(2+) ions. In addition, the sensor could be successfully applied to the detection of intracellular Zn(2+). Meanwhile, the sensor displayed an obvious red color upon selective binding with Fe(2+). Therefore, the sensor could serve as a useful tool for the discrimination of Fe(2+) from Fe(3+) in aqueous media. Moreover, the sensor also showed color changes from yellow to colorless upon selective binding with Zn(2+) and Cu(2+), respectively. The detection limit of the sensor for Cu(2+) (1.5 μM) is far below the guidelines of the World Health Organization (30 μM) as the maximum allowable copper concentration in drinking water, and therefore it is capable of being a practical system for the monitoring of Cu(2+) concentrations in aqueous samples. These results provide a new approach for selectively recognizing the most important three trace elements in the human body simultaneously, for Zn(2+) by emission spectra and Fe(2+), Cu(2+), and Zn(2+) by the naked eye.

Silver-pyrazole complexes as hybrid multifunctional materials with metallomesogenic and photoluminescent behaviour

New pyridine-functionalised pyrazole compounds [Hpz(R(n)py)] (R(n) = C(6)H(4)OC(n)H(2n+1); n = 12, 14, 16, 18; 1-4) and their corresponding silver complexes [Ag(Hpz(R(n)py))(2)][A] ([A] = NO(3)(-), BF(4)(-); ) have been synthesised and characterised. All of them, with the exception of 1, are liquid crystal materials exhibiting monotropic or enantiotropic SmA mesophases, in contrast to the non-mesomorphic related R(n)-monosubstituted compounds. Because the molecular shape is a factor determinant in the organisation of molecules in the liquid crystal phase, we were interested in solving the crystal structure of representative examples of the mentioned compounds, such as 1 and 6. So, the X-ray crystal structure of [Hpz(R(12)py)] 1 shows the presence of dimeric units through N-H···N hydrogen bonds, which conform to an elongated molecular shape containing a double chain length. On the other hand, the structure of [Ag(Hpz(R(14)py))(2)][NO(3)] 6 also evidenced Ag-Ag bonded dimers from 'U'-shaped cationic entities. These dimers exhibit four chains, two by two alternated, so giving rise to a longer molecular length. Of particular interest was to observe that in both structures, the dimers are layer-like packed, their lamellar structures being related to that of the mesophases found in both kinds of compounds. Furthermore, the analysis of the optical data of the compounds 2 and 4 and the silver compounds 5, 6, 9 and 10 as representative examples pointed out their luminescent behaviour as well as their good ability to act as fluorescent probes for Zn(2+), Cu(2+) and Ag(+). An increase in the fluorescence quantum yields is observed in the final complexes produced in the titrations, this fact being specially notable when 9 was used as the starting compound.

Synthesis, spectroscopic, photoluminescence properties and biological evaluation of novel Zn(II) and Al(III) complexes of NOON tetradentate Schiff bases

Novel mononuclear Zn(II) and Al(III) complexes were synthesized from the reactions of Zn(OAc)(2).2H(2)O and anhydrous AlCl(3) with neutral N2O2 donor tetradentate Schiff bases; N,N'bis(salicylaldehyde)4,5-dimethyl-1,2-phenylenediamine (H(2)L(1)) and N,N'bis(salicylaldehyde)4,5-dichloro-1,2-phenylenediamine (H(2)L(2)). The new complexes were fully characterized by using micro analyses (CHN), FT-IR, (1)H NMR, UV-Vis spectra and thermal analysis. The analytical data have been showed that, the stoichiometry of the complexes is 1:1. Spectroscopic data suggested tetrahedral and square pyramidal geometries for Zn(II) and Al(III) complexes, respectively. The synthesized Zn(II), and Al(III) complexes exhibited intense fluorescence emission in the visible region upon UV-excitation in methylene chloride solution at ambient temperature. This high fluorescence emission was assigned to the strong coordination of the ligands to the small and the highly charged Zn(II) and Al(III) ions. Such strong coordination seems to extend the π-conjugation of the complexes. Thermal analysis measurements indicated that the complexes have good thermal stability. As a potential application the biological activity (e.g., antimicrobial action) of the prepared ligands and complexes was assessed by in-vitro testing of their effect on the growth of various strains of bacteria and fungi.

Laterally substituted symmetric and nonsymmetric salicylideneimine-based bent-core mesogens

Bent-core mesogens have gained considerable importance due to their ability to form new mesophases with unusual properties. Relationships between the chemical structure of bent-core molecules and the type and physical properties of the formed mesophases are relatively unknown in detail and differ strongly from those known for calamitic liquid crystals. In this paper symmetric and nonsymmetric five-ring salicylideneaniline-based bent-core mesogens are presented, and the effect of lateral substituents attached at the outer phenyl rings (F, Cl, Br) or the central phenyl ring (CH₃) on the liquid-crystalline behaviour and on the physical properties is studied. Corresponding benzylideneaniline-based compounds were additionally prepared in order to study the influence of the intramolecular hydrogen bond. The occurring mesophases were investigated by differential scanning calorimetry, polarising microscopy, X-ray diffraction and dielectric and electro-optical measurements. The paper reports on new findings with respect to the structure–property relationships of bent-core mesogens. On one hand, the disruptive effect of laterally substituted halogen atoms, F, Cl and Br, on the mesophase behaviour of three isomeric series was much lower than expected. On the other hand, an increase of the clearing temperature by 34 K was observed, caused by small lateral substituents. The electro-optical behaviour, especially the type of polar switching and corresponding molecular movements, is sensitive to variations in the molecular structure.