A hydrogen bond accepting (HBA) scale for anions, including room temperature ionic liquids

Lungwitz, Ralf; Spange, Stefan

doi:10.1039/b714629a

Cited by 268 publications

(242 citation statements)

References 27 publications

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“…Moreover, the chemical shifts of the N-H proton in 1 H NMR spectra indicated the formation of hydrogen bonds with the counterions in solution. The signal of this proton displayed a marked downfield shift when counterion changed from PF 6 À to Cl À , which is in agreement with the reported hydrogen bondaccepting capability of the anions in solutions (PF 6 À oBF 4 À oI À oBr À oCl À ) 26,27 . Previous reports have also confirmed this observation that revealed the formation or strengthening of hydrogen bonds leads to a decrease in the electron density on the bonding hydrogen atom and an increase on the acceptor and donor heteroatoms [28][29][30] , thereby resulting in a downfield shift of the proton chemical shift 31 .…”

Section: Resultssupporting

confidence: 77%

Smart responsive phosphorescent materials for data recording and security protection

et al. 2014

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Smart luminescent materials that are responsive to external stimuli have received considerable interest. Here we report ionic iridium (III) complexes simultaneously exhibiting mechanochromic, vapochromic and electrochromic phosphorescence. These complexes share the same phosphorescent iridium (III) cation with a N-H moiety in the N^N ligand and contain different anions, including hexafluorophosphate, tetrafluoroborate, iodide, bromide and chloride. The anionic counterions cause a variation in the emission colours of the complexes from yellow to green by forming hydrogen bonds with the N-H proton. The electronic effect of the N-H moiety is sensitive towards mechanical grinding, solvent vapour and electric field, resulting in mechanochromic, vapochromic and electrochromic phosphorescence. On the basis of these findings, we construct a data-recording device and demonstrate data encryption and decryption via fluorescence lifetime imaging and time-gated luminescence imaging techniques. Our results suggest that rationally designed phosphorescent complexes may be promising candidates for advanced data recording and security protection. D ata recording, storage and security technologies have been widely utilized in economic and military fields as well as in our daily life. Smart luminescent materials that are responsive to external stimuli have received considerable attention in the construction of optical data recording and storage devices [1][2][3][4][5] . These materials have been classified on the basis of the types of external stimuli that they are responsive to. Mechanochromic materials show changes in emission colour in the presence of mechanical stimuli (for example, shearing, grinding and rubbing) because of the interruption of intermolecular interactions (for example, p-p stacking and hydrogen bonds) [6][7][8][9][10] . Vapochromic luminescence has been observed in materials that are responsive to volatile organic compounds 11,12 . Electric field is an important external stimulus. Electrochromism occurs in p-conjugated polymers because of the reversible transition between two redox states [13][14][15][16] . However, materials showing electrochromic luminescence, which is distinct luminescence colour responses to an electric field, are scarce. We envision the potential commercial applications of electrochromic luminescent materials because they can be conveniently integrated into semiconductor-based electronic devices. In addition, it is conceivable that compounds simultaneously showing mechanochromic, vapochromic and electrochromic luminescence are of great use to the development of multifunctional materials.Phosphorescent transition-metal complexes, such as those of Ir(III) and Pt(II), have been extensively studied for various photonic and electronic applications because of their rich excited-state properties, including high luminescence quantum yields, long emission lifetimes, large Stokes shifts, high photostability and various luminescence colours [17][18][19][20] . These complexes have also been utilized a...

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Section: Resultssupporting

confidence: 77%

Smart responsive phosphorescent materials for data recording and security protection

et al. 2014

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“…The analysis of the 1 H-NMRspectra of pure ILs, where additional solvent interactions can be ruled out, reveals that the increasing size of the anion, accompanied by gradual reduction in anion basicity, leads to a reduction in H-bonding, which is in line with fi ndings from other groups measuring ILs in organic solvents. [ 91,92 ] The 13 C-NMR signals of the imidazolium ring are only weakly infl uenced by the nature of the anion. However, a small shift of the signal from the carbon atom in 2-position refl ects an anion-dependent change of electronic structure within the ring, which is likely related to alterations in ring hybridization, an argument that is also supported by our NBO analysis.…”

Section: Progress Reportmentioning

confidence: 99%

Surface Science and Model Catalysis with Ionic Liquid‐Modified Materials

et al. 2011

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Materials making use of thin ionic liquid (IL) films as support-modifying functional layer open up a variety of new possibilities in heterogeneous catalysis, which range from the tailoring of gas-surface interactions to the immobilization of molecularly defined reactive sites. The present report reviews recent progress towards an understanding of "supported ionic liquid phase (SILP)" and "solid catalysts with ionic liquid layer (SCILL)" materials at the microscopic level, using a surface science and model catalysis type of approach. Thin film IL systems can be prepared not only ex-situ, but also in-situ under ultrahigh vacuum (UHV) conditions using atomically well-defined surfaces as substrates, for example by physical vapor deposition (PVD). Due to their low vapor pressure, these systems can be studied in UHV using the full spectrum of surface science techniques. We discuss general strategies and considerations of this approach and exemplify the information available from complementary methods, specifically photoelectron spectroscopy and surface vibrational spectroscopy.

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“…13,15,17,[22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][47][48][49][50][51] It should be highlighted that the hydrogen-bond acceptor strength of an IL is dominated by its anion while the hydrogen-bond donor ability is essentially controlled by the cation and only slightly depends upon the anion of the IL. 18,19 Thus, and since we were focused on developing an extended series for the hydrogen-bond acidity of ILs, ILs comprising a fixed anion ([NTf 2 ] − ) and a wide range of cations (imidazolium-, pyridinium-, piperidinium-, pyrrolidinium-, ammonium-, sulfonium-, and phosphonium-based) were selected.…”

Section: Introductionmentioning

confidence: 99%

Hydrogen-bond acidity of ionic liquids: an extended scale

Kurnia

Lima

Cláudio

et al. 2015

Phys. Chem. Chem. Phys.

101

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One of the main drawbacks comprising an appropriate selection of ionic liquids (ILs) for a target application is related to the lack of an extended and well-established polarity scale for these neoteric fluids. Albeit considerable progress has been made on identifying chemical structures and factors that influence the polarity of ILs, there still exists a high inconsistency in the experimental values reported by different authors. Furthermore, due to the extremely large number of possible ILs that can be synthesized, the experimental characterization of their polarity is a major limitation when envisaging the choice of an IL with a desired polarity. Therefore, it is of crucial relevance to develop correlation schemes and a priori predictive methods able to forecast the polarity of new (or not yet synthesized) fluids. In this context, and aiming at broadening the experimental polarity scale available for ILs, the solvatochromic Kamlet-Taft parameters of a broad range of bis(trifluoromethylsulfonyl)imide-([NTf 2 ] − )-based fluids were determined. The impact of the IL cation structure on the hydrogen-bond donating ability of the fluid was comprehensively addressed. Based on the large amount of novel experimental values obtained, we then evaluated COSMO-RS, COnductor-like Screening MOdel for Real Solvents, as an alternative tool to estimate the hydrogen-bond acidity of ILs. A three-parameter model based on the cation-anion interaction energies was found to adequately describe the experimental hydrogen-bond acidity or hydrogen-bond donating ability of ILs. The proposed three-parameter model is also shown to present a predictive capacity and to provide novel molecular-level insights into the chemical structure characteristics that influence the acidity of a given IL. It is shown that although the equimolar cation-anion hydrogen-bonding energies (E HB ) play the major role, the electrostaticmisfit interactions (E MF ) and van der Waals forces (E vdW ) also contribute, admittedly in a lower extent, towards the hydrogen-bond acidity of ILs. The new extended scale provided for the hydrogen-bond acidity of ILs is of high value for the design of new ILs for task-specific applications. † Electronic supplementary information (ESI) available: Comparison between experimental and literature solvatochromic values; correlation between experimental and predicted hydrogen-bond acidity; equation to calculate the absolute relative deviation. See

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A hydrogen bond accepting (HBA) scale for anions, including room temperature ionic liquids

Abstract: A hydrogen bond accepting (HBA) ability scale for anions of room temperature ionic liquids (RTILs) has been determined by means of 1 H NMR spectroscopy and a solvatochromic UV/vis probe.Scheme 1 Structure of dye 1 used in this work to determine the b values of RTILs.

Cited by 268 publications

References 27 publications

Smart responsive phosphorescent materials for data recording and security protection

Smart responsive phosphorescent materials for data recording and security protection

Surface Science and Model Catalysis with Ionic Liquid‐Modified Materials

Hydrogen-bond acidity of ionic liquids: an extended scale

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