Highly luminescent organic-inorganic hybrid materials have been prepared by combining task-specific polymerized ionic liquids (PILs) based on the 1-alkyl-3-vinylimidazolium cation ([CnVim]+ (with n = 2-6)) with suitable halides of trivalent lanthanides such as europium and terbium. The resulting materials have been characterized by 1H nuclear magnetic resonance, Fourier transform infrared, UV-Vis and photoluminescence spectroscopy. They show bright and intense luminescence over a wide range of excitation wavelengths, which particularly for the Eu3+ containing compounds, benefits from efficient energy transfer from the organic aromatic moieties in the PIL to the emitting level of the lanthanide(iii) ion. In the case of the Tb3+ ion, the emission benefits from excitation into the Tb3+ d levels. The emission colour can be tuned from green to red for Tb and Eu respectively. This includes bright white emission for Eu that can be achieved by altering the excitation wavelength. The easy processability of these novel PILs renders them interesting for a wide range of optical applications.

Since the discovery of AlQ3 (Q = 8-quinolinolato) quinolinato complexes, they have been extensively scrutinized as emitter materials for organic lighting. Herein, we report on the first representatives of a series of tetrabutylphosphonium tetrakis(8-quinolinolato)lanthanidate complexes [P4444][Ln(Q)4]·2X (Ln = Dy-Lu and Y; X = H2O for Ln = Dy-Tm, Lu and Y and (CH3)2CO for Ln = Yb), which are synthesised by a simple metathesis reaction of the respective potassium tetrakis(8-quinolinolato)lanthanidate salts with tetrabutylphosphonium bromide in acetone at room temperature. Single-crystal X-ray diffraction reveals that Ln(iii) is coordinated by four bidentate 8-quinolinato ligands in the form of a distorted square antiprism. The distinct [Ln(Q)4]− anions interact with the [P4444]+ cations through secondary bonding interactions, such as CH-π and van der Waals interactions, in addition to electrostatic coulombic interactions. Although these compounds contain crystal water/solvent molecules (and their synthesis does not require an inert atmosphere), they do not enter the metal coordination sphere but form pairwise intramolecular hydrogen bonds with the two 8-quinolinato ligands of the complex lanthanide anions. Combined differential scanning calorimetry-thermogravimetric analysis indicates that crystal water is lost at around 100 °C and [P4444][Ln(Q)4] is formed, which is stable up to 300 °C, where further degradation occurs. All compounds feature strong emission in the green region, originating from the π* → π transitions within the 8-quinolinato ligand, with lifetimes in the nanosecond range. The luminescence colour changes from blue-green to yellow-green depending on Ln3+, which opens up additional directions in the colour tuning of emitters for organic lighting applications.

A set of IL-forming ion combinations has been studied to gain a deeper understanding of how, aside from obvious electrostatic interactions and ion size effects, secondary bonding such as hydrogen as well as halogen bonding and van der Waals interactions along with conformational and structural flexibility influence the crystallization behavior of potentially IL forming salts. The scrutinized ions have been specifically chosen to allow for unraveling preferential interactions of functional groups that may favor or disfavor crystallization with respect to secondary bonding interactions, i.e., primary and quaternary ammonium cations of variable alkyl chain lengths, which were also endowed with hydroxy groups, combined with formate and bis(trifluoromethanesulfonyl)amide anions. The background is to provide a deeper fundamental understanding of how to intentionally pair cations and anions that will not support the formation of a crystalline solid but rather IL formation, an approach described as “anti-crystal engineering”. This concept is based on the idea to avoid combining ions that are strong supramolecular synthons for crystallization. To this avail, the crystallization behavior of salts constituted of combinations of selected ions bearing different structural, supramolecular crystallization motifs has been studied in detail by low-temperature differential scanning calorimetry (DSC). Single crystal X-ray structure analysis has been used to elucidate ion packing and preferential interactions whenever crystalline solid formation is observed. The study reveals that the lowest melting points are supported by cation-anion combinations that have the least hydrogen bonding. However, if there are multiple possibilities of H-bonding for an ion with its counteranion, this bonding frustration leads as well to low melting points-albeit they are still higher compared to ion combinations with no H-bonding capacity. Through a careful balance of primary and secondary, directional and nondirectional interactions, it was possible to rationally identify a record class of ionic liquids, which combine exceptionally high decomposition points (440-450 °C) with an enormously high liquid range around of more than 500 °C and no tendency for solidification down to well below ambient temperature (−90 °C). These ILs are formed by bis(trifluoromethane)sulfonylamides with quaternary ammonium ions that bear an −OH group in the side chain.

Commercial (protiated) samples of the green and biodegradable bioester 2-ethylhexyl laurate (2-EHL) were mixed with D-2-EHL synthesized by hydrothermal deuteration, with the mixtures demonstrating bulk structuring in small-angle neutron scattering measurements. Analysis in a polymer scattering framework yielded a radius of gyration (R (g)) of 6.5 angstrom and a Kuhn length (alternatively described as the persistence length or average segment length) of 11.2 angstrom. Samples of 2-EHL dispersed in acetonitrile formed self-assembled structures exceeding the molecular dimensions of the 2-EHL, with a mean aggregation number (N-agg) of 3.5 +/- 0.2 molecules across the tested concentrations. We therefore present structural evidence that this ester can function as a nonionic (co)-surfactant. The available surfactant-like conformations appear to enable performance beyond the low calculated hydrophilic-lipophilic balance value of 2.9. Overall, our data offer an explanation for 2-EHL's interfacial adsorption properties via self-assembly, resulting in strong emolliency and lubricity for this sustainable ester-based bio-oil.

Emerging organic light-emitting devices, such as light-emitting electrochemical cells (LECs), offer a multitude of advantages but currently suffer from that most efficient phosphorescent emitters are based on expensive and rare metals. Herein, it is demonstrated that a rare metal-free salt, bis(benzyltriphenylphosphonium)tetrabromidomanganate(II) ([Ph₃PBn]₂[MnBr₄]), can function as the phosphorescent emitter in an LEC, and that a careful device design results in the fact that such a rare metal-free phosphorescent LEC delivers broadband white emission with a high color rendering index (CRI) of 89. It is further shown that broadband emission is effectuated by an electric-field-driven structural transformation of the original green-light emitter structure into a red-emitting structure. 

Light-emitting materials based on earth-abundant metals, such as manganese hold great promise as emitters for organic lighting devices. In order to apply such emitter materials and, in particular, to overcome the problem of self-quenching due to cross-relaxation, we investigated a series of tetrabromidomanganate ([MnBr₄]²⁻) salts with bulky tetraalkylphosphonium counter cations [P_nnn]⁺, namely [P_nnnn]₂[MnBr₄] (n = 4 (1), 6 (2) and 8 (3)), which can be obtained by a straightforward reaction of the respective phosphonium bromide and MnBr₂. Variation of the cation size allows control of the properties of the resulting ionic materials. 1 and 3 qualify as ionic liquids (ILs), where 1 features a melting point of 68 °C, and 3 is liquid at room temperature and even at very low temperatures. Furthermore, 1 and 2 show the formation of higher-ordered thermotropic mesophases. For 1 a transition to a thermodynamically metastable smectic liquid crystalline phase can be observed at room temperature upon reheating from the metastable glassy state; 2 appears to form a plastic crystalline phase at ∼63 °C, which persists up to the melting point of 235 °C. The photoemission is greatly affected by phase behaviour and ion dynamics. A photoluminescence quantum yield of 61% could be achieved, by balancing the increase in Mn²⁺-Mn²⁺ separation and reducing self-quenching through increasingly large organic cations which leads to adverse increased vibrational quenching. Compared to analogous ammonium compounds, which have been promoted as @#x0308;inorganic hybrid perovskite, the phosphonium salts show superior performance, with respect to photoluminescent quantum yield and thermal and air/humidity stability. As the presented compounds are not sensitive to the atmosphere, in particular moisture, and show strong visible electroluminescence in the green region of light, they are important emitter materials for use in organic light-emitting devices.

In search of ionic liquids (ILs) with multiple types of soft donor atoms capable of preferentially complexing a range of soft metal ions over harder ions, we investigated structural clues to the role of hydrogen bonding in IL behavior through a series of salts with anions containing both N- and S-donor atoms based on azole thiolates. Reaction of equimolar amounts of triethylamine (Et₃N) or diisobutylamine (DBA) with 1-phenyl-1H-tetrazole-5-thiol (PhTzSH), 1-methyl-1H-tetrazole-5-thiol (MeTzSH), or 5-methyl-1,3,4-dithiazole-2-thiol (MeDiTSH) yielded [Et₃NH][MeTzS] (1), a yellow liquid, and the low melting yellow solids [DBAH][MeTzS] (2), [Et₃NH][PhTzS] (3), [DBAH][PhTzS] (4), [Et₃NH][MeDiTS] (5), and [DBAH][MeDiTS] (6). Thermal analysis revealed that all of them qualify as ILs with melting points below 100 °C. Single crystal X-ray structure analysis of 2–6 revealed the presence of an extensive H-bonding network that includes the rare N–H⋯S hydrogen bonds in 3, 4, and 6. These weaker interactions appear to significantly influence thermal behavior, where strong bonding leads to higher melting temperatures and lower decomposition points.

A series of 19 ionic liquids (ILs) based on phosphonium and imidazolium cations of varying alkyl-chain lengths with the orthoborate anions bis(oxalato)borate [BOB]⁻, bis(mandelato)borate, [BMB]⁻ and bis(salicylato)borate, [BScB]⁻, are synthesized and studied using small-angle neutron scattering (SANS). All measured systems display nanostructuring, with 1-methyl-3-n-alkyl imidazolium-orthoborates forming clearly bicontinuous L₃ spongelike phases when the alkyl chains are longer than C₆ (hexyl). L₃ phases are fitted using the Teubner and Strey model, and diffusely-nanostructured systems are primarily fitted using the Ornstein-Zernicke correlation length model. Strongly-nanostructured systems have a strong dependence on the cation, with molecular architecture variation explored to determine the driving forces for self-assembly. The ability to form well-defined complex phases is effectively extinguished in several ways: methylation of the most acidic imidazolium ring proton, replacing the imidazolium 3-methyl group with a longer hydrocarbon chain, substitution of [BOB]⁻ by [BMB]⁻, or exchanging the imidazolium for phosphonium systems, irrespective of phosphonium architecture. The results suggest there is only a small window of opportunity, in terms of molecular amphiphilicity and cation:anion volume matching, for the formation of stable extensive bicontinuous domains in pure bulk orthoborate-based ILs. Particularly important for self-assembly processes appear to be the ability to form H-bonding networks, which offer additional versatility in imidazolium systems. 

Albeit tris(8-hydroxyquinolinato) aluminum (Alq₃) and its derivatives are prominent emitter materials for organic lighting devices, and the optical transitions occur among ligand-centered states, the use of metal-free 8-hydroxyquinoline is impractical as it suffers from strong nonradiative quenching, mainly through fast proton transfer. Herein, it is shown that the problem of rapid proton exchange and vibration quenching of light emission can be overcome not only by complexation, but also by organization of the 8-hydroxyquinolinium cations into a solid rigid network with appropriate counter-anions (here bis(trifluoromethanesulfonyl)imide). The resulting structure is stiffened by secondary bonding interactions such as π-stacking and hydrogen bonds, which efficiently block rapid proton transfer quenching and reduce vibrational deactivation. Additionally, the optical properties are tuned through methyl substitution from deep blue (455 nm) to blue-green (488 nm). Time-dependent density functional theory (TDFT) calculations reveal the emission to occur from which an unexpectedly long-lived S₁ level, unusual for organic fluorophores. All compounds show comparable, even superior photoluminescence compared to Alq₃ and related materials, both as solids and thin films with quantum yields (QYs) up to 40–50%. In addition, all compounds show appreciable thermal stability with decomposition temperatures above 310 °C.

Lanthanide (Ln) metals are strong reducing agents (E⁰(Ln³⁺/Ln⁰)≈−2.3 V vs. NHE) which can be applied in various manners in organic synthesis. While samarium and ytterbium have been employed for more than 50 years, the last 20 years have seen the emergence of synthetic applications using other metals, such as lanthanum, cerium, praseodymium, neodymium or dysprosium. The large electron reservoir of lanthanide metals, the Lewis acidic character of the Ln³⁺ ions and their intermediate electronegativity compared to lithium or magnesium can provide unique reactivity patterns. This review provides an overview on the potential of these metals for synthetic organic chemistry in the following areas: 1) for Grignard type reactivity and radical generation, 2) in reduction chemistry involving carbonyl compounds and dehalogenation reactions and 3) in combination with transition metals.