Luminescent Ionic Liquids Research Articles

Photoluminescent ionic liquid-poly(vinylidene fluoride) hybrid materials for UV-Vis filter applications

Smart multifunctional materials have been increasingly applied in different fields of knowledge. In particular, photoluminescent materials have been explored for displays, radiation detection, lamps or anti-counterfeiting applications, among others. This work reports the development of photoluminescent materials based on poly(vinylidene fluoride) (PVDF) polymer incorporating different contents (0, 5, 10, and 20 % w/w) of the luminescent ionic liquid (IL) 1-butyl-3-methylimidazolium tetrakis(thenoyltrifluoroacetonato)europate(III) ([Bmim][Eu(tta)4]). The inclusion of the IL induced an increase of roughness and a slightly porous structure. No changes occur in the PVDF chemical structure and thermal behaviour. A decrease in the Young Modulus was observed, from 1.75×103 ± 1.56×102 to 5.09×102 ± 2.07×102 MPa for the sample incorporating 20 % w/w of IL which acted as a plasticizer. Further, the presence of ionic charges promoted an increase in electrical conductivity. The influence of IL content on the luminance was evaluated and a proof of concept demonstrating the potential of the composites as a UV–vis filter converter is provided.

Mesomorphism, high-contrast negative fluorosolvatochromism and photoinduced fluorescence conversion of thienylcyanostyrene-pyridinium salts

Novel thienylcyanostyrene and pyridinium-based luminescent ionic liquid crystals (ILCs) characterized with different length of N-alkyl chains (N–C3H7 and N–C8H17) and different size of counter anions (Br−, BF4−, PF6− and Tf2N−) on pyridinium moiety have been synthesized. The chemical modifications of N-alkyl chains and counter anions are easily achieved via pyridine alkylation followed with further ion exchanges, which played a key role in tuning supramolecular self-assembly of these ILCs. The compounds with shorter N–C3 alkyl chain (E-CTPC3X, X = Br−, BF4−, PF6− and Tf2N−) can self-assemble into 3D cubic phase or 2D hexagonal columnar phase depending on the size of counter anion, while the analogues with longer N–C8 alkyl chain (E-CTPC8X, X = BF4− and Tf2N−) only result smectic A phases. Moreover, the prolongation of the N-alkyl chain or enlargement of counter anion could significantly decrease the clear points of LC phases avoiding the thermal decomposition at high temperature, whereas introducing counter anions such as BF4−, PF6− that can form hydrogen bonds have stabilized the LC phases. The notable negative fluorosolvatochromism and the photoinduced fluorescence conversion with high-contrast of these ILCs were observed using UV–vis absorption and photoluminescence (PL) spectra, and was further analyzed by dynamic 1H NMR. These ILCs had been used as dopant to modify the n-Si/PEDOT:PSS heterojunction solar cells (HSCs) with 2 fold hole mobility (μhole) enhancement of the PEDOT:PSS layer.

Luminescent Rhenium-containing Ionic Liquid Exhibiting Photoinduced Vapochromism

Abstract A luminescent ionic liquid containing a cationic rhenium tricarbonyl complex was synthesized. UV photoirradiation of this liquid in the presence of an organic solvent vapor caused a color change and luminescence quenching via photochemical ligand exchange, thereby enabling the photocontrol of vapochromism.

Luminescent ionic liquid formed from a melted rhenium(v) cluster.

Recently, non-crystalline coordination materials have been shown to represent a versatile class of functional materials. However, such materials incorporating metal complex clusters have remained largely unexplored. Herein, we demonstrate that a luminescent tetranuclear ReV cluster melts at 489 K, with the cluster structure being maintained in the corresponding supercooled ionic liquid phase.

Highly Luminescent Ionic Liquids Based on Complex Lanthanide Saccharinates

Four strongly luminescent ionic liquids with complex lanthanide saccharinate anions, [C4mim]3[Eu(Sac)6(H2O)2] (1), {C4mpy}5{[Ln(Sac)6(H2O)2][Ln(Sac)5(H2O)3]}{(H2O)2(CH3CN)2} (Ln = Sm for 2a; Ln = Eu for 2b), and [C4mpy]3[Eu(Sac)6][CH3CN] (3) (C4mim = 1-butyl-3-methylimidazolium; C4mpy = N-butyl-4-methylpyridinium; Sac = saccharinate), have been obtained by reacting the ionic liquids 1-butyl-3-methylimidazolium saccharinate, [C4mim][Sac], and N-butyl-4-methylpyridinium saccharinate, [C4mpy][Sac], with the respective lanthanide saccharinates. Single-crystal X-ray diffraction analyses reveal the respective lanthanide center to be six- or eight-coordinated by five or six saccharinate anions and two or three aqua ligands in the cases of 1 and 2 when lanthanide saccharinated hydrate was employed as the starting material. Coordination of water to the lanthanide can be avoided when using the anhydrous lanthanide saccharinate as shown by the structure of 3. Using a co-solvent, acetonitrile, to facilitate the reaction led to incorporation of solvent molecules into the crystal structure of the final materials (2 and 3). Differential scanning calorimetry analyses reveal that 1 is an ionic liquid whereas 2 and 3 are low-temperature molten salts. The three europium(III)-containing compounds (1, 2b, and 3) all show characteristic intense red emissions of Eu(III) upon excitation into levels of the saccharinate ligands (321 nm) or Eu(III) (393 nm). At room temperature, the decay times of 1 and 2b are all ∼0.5 ms, whereas the decay time of 3 amounts to 3.85 ms due to removal of aqua ligands in the first coordination sphere; accordingly, the quantum efficiencies of 1, 2b, and 3 were determined to be 15.9%, 22.95%, and 57.75%, respectively. The CIE chromaticity coordinates for all Eu compounds are in the red region and approach the NTSC standard CIE values when the temperature is increased. Sm(III)-containing compound 2a shows characteristic Sm(III) emission peaks. As expected, the CIE coordinates of samarium compound 2a fall in the orange-red region.

Designing Polymorphic Bi3+-Containing Ionic Liquids for Stimuli-Responsive Luminescent Materials.

Solid-state luminescent materials that possess reversible fluorescence changes toward external multistimuli are of immense interest because of their potential applications in data storage and sensors. While the recent developments in this field are mainly focused on the π-conjugated organic molecules. Herein two polymorphic luminescent ionic liquid (IL)-based stimuli-responsive materials were designed by the supramolecular assemblies of an organic-decorated chlorobismuthate anion and a rotationally flexible imidazolium cation, namely, α (1)/β (2)-[Bmmim][BiCl4(2,2'-bpy)] (Bmmim = 1-butyl-2,3-dimethylimidazolium; 2,2'-bpy = 2,2'-bipyridine). Because of the different conformations of the n-butyl chains on the imidazolium cations, tuning of the supramolecular packing structures as well as luminescent colors for 1 and 2 was realized. Single-crystal X-ray diffraction and Hirshfeld surface analyses disclose that the polymorphism-dependent emission may be attributed to the different weak interactions, especially to the π-π interactions between adjacent [BiCl4(2,2'-bpy)]- anions in two compounds. Additionally, compound 2 could be transformed into 1 spontaneously at ambient conditions, which could be triggered by the moisture in the air. Both of the title compounds could detect NH3 vapor selectively through the luminescence "turn-off" method rapidly and reversibly because of the destruction of intermolecular interactions, indicating their stimuli-responsive property toward NH3.

Luminescent ionic liquids based on cyclometalated platinum(ii) complexes exhibiting thermochromic behaviour in different colour regions.

Luminescent ionic liquids, based on anionic Pt(ii) complexes, were developed. Depending on the cyclometalating ligands used, they exhibit thermochromic luminescence with different colours. The chromic properties in the flexible liquid and glass states emerge through the self-assembling character of the square-planar Pt(ii) complexes.

The effect of three luminescent ionic liquids on corroded glass surfaces – A first step into stained-glass cleaning

Corrosion in medieval stained-glass represents a challenging issue in Conservation Science, being mainly composed by calcium salts. Model glass materials were produced and then subjected to an accelerated corrosion environment. Early stage glass corrosion layers observed were afterwards cleaned with luminescent ionic liquids (ILs). The effectiveness of the treatment was compared with Ethylenediaminetetraacetic acid solution and high levels of humidity, both of which have caused alterations on the glass surface. With the ILs, detectable morphological or chemical alterations were avoided and the gel-layer remains on the glass surface, indicating that these are a viable alternative to conventional cleaning methods.

Piezoluminescence and Liquid Crystallinity of 4,4′-(9,10-Anthracenediyl)bispyridinium Salts

Piezoluminescence and liquid crystallinity of anthracene-based bispyridinium salts were investigated in stimulus-responsive luminescent organic crystals and luminescent ionic liquid crystals. The salts possess an anthracene moiety as a fluorophore in their center, and the pyridiniums attached to the anthracene moiety are substituted with trialkoxybenzyl groups. Single crystals of the salts bearing two trimethoxybenzyl groups were obtained as solvates. Ethyl acetate, acetone, and dioxane solvates of the chlorides have almost the same crystal structures with one-dimensional channels. Grinding of the solvated crystals caused the extrusion of the included solvent molecules, which resulted in the red shifts of their fluorescence in the solid state. The dimethyl sulfoxide solvate of the hexafluorophosphate also showed piezoluminescene by grinding. Tris(octyloxy)benzyl and tris(dodecyloxy)benzyl derivatives exhibited rectangular columnar liquid crystals upon being heated for their bromide and tetrafluoroborate s...

Luminescent dansyl-based ionic liquids from amino acids and methylcarbonate onium salt precursors: synthesis and photobehaviour

Luminescent ionic liquids (LILs) bearing the dansyl chromophore were prepared from two aminoacids, a dipeptide, and onium salts precursors using innovative eco-friendly protocols.

Full-Color Tunable Photoluminescent Ionic Liquid Crystals Based on Tripodal Pyridinium, Pyrimidinium, and Quinolinium Salts

Color-tunable luminescent ionic liquid crystals have been designed as a new series of luminescent materials. To achieve tuning of emission colors, intramolecular charge transfer (ICT) character has been incorporated into tripodal molecules. A series of the compounds has three chromophores in each molecule, incorporated with both electron-donating moieties such as alkylaminobenzene and alkoxybenzene, and electron-accepting moieties such as pyridinium, pyrimidinium, and quinolinium parts. These C(3)-symmetrical molecules self-assemble into liquid-crystalline (LC) columnar (Col) structures over wide temperature ranges through nanosegregation between ionic moieties and nonionic aliphatic chains. Photoluminescent (PL) emissions of these tripodal molecules are observed in the visible region both in the self-assembled condensed states and in solutions. For example, a pyrimidinium salt with didodecylaminobenzene moieties exhibits yellowish orange emission (λ(em) = 586 nm in a thin film). Multicolor PL emissions are successfully achieved by simple tuning of changing electron-donating and electron-accepting moieties of the compounds, covering the visible region from blue-green to red. It has been revealed that ICT processes in the excited states and weak intermolecular interactions play important roles in the determination of the PL properties of the materials, by measurements of UV-vis absorption and emission spectra, fluorescence lifetimes, and PL quantum yields.

Influence of the liquid crystal behaviour on the Langmuir and Langmuir–Blodgett film supramolecular architecture of an ionic liquid crystal

A new luminescent ionic liquid crystal, called Ipz-2, has been synthesised and its mesophase behaviour and also at the air–liquid interface has been studied and compared with Ipz, another ionic pyrazole derivative, with a similar molecular structure, previously studied. The X-ray diffraction pattern shows that Ipz-2 exhibits hexagonal columnar mesomorphism, while Ipz adopts lamellar mesophases. Langmuir films of both compounds are flat and homogeneous at large areas per molecule, but create different supramolecular structures under further compression. Ipz-2 Langmuir films have been transferred onto solid substrates, and Atomic Force Microscopy (AFM) images of the Langmuir–Blodgett films have shown that large columnar structures hundreds of nm in diameter are formed on top of the initial monolayer, in contrast with well-defined trilayer LB films obtained for Ipz. Our results show that Ipz-2 has a tendency to stack in columnar arrangements both in liquid crystalline bulk and in Langmuir and Langmuir–Blodgett films.

‘Liquid litmus’: chemosensory pH-responsive photonic ionic liquids

We report on the founding member of a unique class of luminescent ionic liquids integrating a photoacidic anion that responds to the presence of both condensed- and gas-phase basicity; the analytical response is ratiometric in nature, visible to the naked eye, and offers fascinating prospects in smart photofluids, liquid logic gates, electronic noses, and sensory inks.

Supramolecular Architecture in Langmuir Films of a Luminescent Ionic Liquid Crystal

A new luminescent ionic liquid crystal (ILC) with a positive charge in the aromatic central core and two hydrophobic alkyl chains at the ends, called Ipz, has been synthesized and its behavior at the air−liquid (NaCl 2 × 10−6 M) interface has been characterized by combination of surface pressure and surface potential versus area per molecule (π−A and ΔV−A) isotherms, Brewster angle microscopy (BAM) and UV−vis reflection spectroscopy. The results indicate the formation of a supramolecular architecture at the air−liquid interface formed by a head-to-head bilayer on top of a flat-core monolayer. Langmuir films were transferred onto solid substrates, and atomic force microscopy (AFM) and X-ray reflection (XRR) have confirmed that well-ordered multilayer films are obtained. Langmuir films supramolecular structure is different from the molecular organization of Ipz in lamellar liquid-crystalline phases. Furthermore, fluorescence emission spectra reveal a blue shift of the emission band of about 18 nm when compa...

Thermotropic Ruthenium(II)-Containing Metallomesogens Based on Substituted 1,10-Phenanthroline Ligands

Imidazo[4,5-f]-1,10-phenanthroline and pyrazino[2,3-f]-1,10-phenanthroline substituted with long alkyl chains are versatile ligands for the design of metallomesogens because of the ease of ligand substitution. Whereas the ligands and the corresponding rhenium(I) complexes were not liquid-crystalline, mesomorphism was observed for the corresponding ionic ruthenium(II) complexes with chloride, hexafluorophosphate, and bistriflimide counterions. The mesophases were identified as smectic A phases by high-temperature small-angle X-ray scattering (SAXS) using synchrotron radiation. The transition temperatures depend on the anion, the highest temperatures being observed for the chloride salts and the lowest for the bistriflimide salts. The ruthenium(II) complexes are examples of luminescent ionic liquid crystals.