Estimating Enthalpies of Vaporization of Imidazolium‐Based Ionic Liquids from Far‐Infrared Measurements

Fumino, Koichi; Wulf, Alexander; Verevkin, Sergey P.; Heintz, Andreas; Ludwig, Ralf

doi:10.1002/cphc.201000140

Cited by 71 publications

(71 citation statements)

References 34 publications

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“…Owing to the low emission quantum yield of 1·I in the solid state, we chose fi ve counteranions (i.e., NTf 2 − , PF 6 − , OTf − , BF 4 − , and N(CN) 2 − ) to illustrate the correlation between the cation-anion interaction and the mechanochromic performance of 1·X (X = counteranion). After three minutes of pressing under 6 MPa using an oil press, 1·NTf 2 , 1·PF 6 , 1·OTf , 1·BF 4 , and 1·N(CN) 2 underwent redshifts of the peak emission wavelengths (approximately 102 nm, 90 nm, 78 nm, 36 nm, and 7 nm, respectively) ( Table 1 and Figure 1 a), which was in good agreement with the known order of the strength of the cation-anion interaction as following: [22][23][24][25] It hinted that the strength of the cation-anion interaction could determine the mechanochromic luminescence property to a certain extent. The NTf 2 − anion associated with the delocalization of negative charge and the shielding effect of the sulfonyl oxygens and trifl uoromethane groups is widely used to reduce the capacity of the cationanion interaction to develop low melting ionic liquids.…”

Section: Introductionsupporting

confidence: 75%

“…[ 1,11,15 ] It is well-known that the cation-anion interaction is one of the important interactions to govern the molecular packing modes of onium salts and, thus, can lead to changes in the properties such as melting point, density, viscosity, and electrical conductivity. [22][23][24][25] Given that the molecular assemblies of organic cations with a rich set of anions can offer a great abundance of cation-anion interactions, we envisioned that the cation-anion interactions and other intra-and intermolecular interactions could be regarded as ideal competing factors to reach such a balance through the variation of counteranions. Thus, onium salts would be promising candidates for mechanochromic luminescent materials.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Cation–Anion Interaction‐Directed Molecular Design Strategy for Mechanochromic Luminescence

Song

et al. 2013

Adv Funct Materials

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Mechanofl uorochromic materials have great potential for a wide variety of applications such as sensors, memory devices, motion systems, security systems, and so forth. However, only few design principles have been disclosed, which greatly impedes the growth of mechanofl uorochromic dyes. Here, a strategy of molecular design for mechanochromic luminescence is reported, based on the cation-anion interaction-directed switching of molecular stacking. On the basis of this strategy, a series of common N-heteroaromatic onium fl uorophores such as imidazolium, 1,2,4-triazolium, triazolopyridinium, benzoimidazolium, γ -carbolinium, and pyridinium salts have been designed and proved to have striking reversible mechanofl uorochromic behaviors. The simple attachment of a non-fl uorescent imidazolium unit to the pyrene scaffold through a fl exible carbon chain can even trigger the mechanofl uorochromic phenomenon, which gives a consummate interpretation that the cation-anion interaction can be considered as an important general tool to design organic mechanochromic luminescent materials.

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Section: Introductionsupporting

confidence: 75%

Section: Introductionmentioning

confidence: 99%

Cation–Anion Interaction‐Directed Molecular Design Strategy for Mechanochromic Luminescence

Song

et al. 2013

Adv Funct Materials

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“…[40] This relation between FIR frequency shifts and changing interaction strengths provides further options. Frequency shifts in the far-infrared spectra can be referred to stronger or weaker interactions in these Coulomb fluids.…”

Section: Methodsmentioning

confidence: 99%

Dissecting Anion–Cation Interaction Energies in Protic Ionic Liquids

Fumino¹,

Fossog²,

Wittler³

et al. 2013

Angew Chem Int Ed

Self Cite

110

119

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Knowledge of intermolecular forces is a requisite for understanding material properties. These forces determine whether matter sticks together, gases condense to liquids, and liquids freeze to solids. The study of these forces in ionic liquids is particularly interesting. [1][2][3][4] Although the structure and properties of these fluid materials are determined to a large extent by the Coulomb forces, hydrogen bonding and dispersion forces can play a crucial role. The strong anion-cation interaction in these Coulomb fluids is reflected in their extremely low vapor pressures and high enthalpies of vaporization. [5][6][7][8][9][10][11][12] These properties, among others, make ionic liquids (ILs) attractive for science and technology.However, measuring intermolecular interactions in ionic liquids is still a challenge. In principle these interactions can be studied by experimental techniques that cover the frequency range of these interaction energies. Meanwhile there are numerous spectroscopic techniques available covering the frequency range of interest between 1 and 300 cm À1 , corresponding to 0.03 and 9 THz. The palette of spectroscopic methods includes optical heterodyne-detected Ramaninduced Kerr effect (RIKE), far-infrared (FIR), Raman, and THz spectroscopy as well as low-energy neutron scattering. [13][14][15][16][17][18][19][20][21][22][23] Although it has been shown that this spectral region may be extremely useful for studying intermolecular forces, we concede that the measured spectra are quite complicated and difficult to dissect. In particular the unequivocal assignment of the vibrational bands to intermolecular interactions is a challenge. Low-frequency absorption can arise from internal molecular vibrations, librational modes, and torsional modes such as alkyl group rotation. Usually, DFT and MD methods are required for the interpretation of the measured spectra. [24][25][26][27][28][29][30][31] In principle, these methods are suitable to indicate low-frequency intramolecular vibrational modes.However, a serious problem still remains. It is not clear to what extent DFT methods or force fields typically used in classical molecular dynamics (MD) simulations are able to describe intermolecular interactions accurately. [32] In principle ab initio molecular dynamics (AIMD) simulation is the method of choice for analyzing this frequency range, as shown by Heyden et al. for the case of liquid water. [33] However, for the relatively viscous ionic liquids the small system sizes and short simulation runs provide insufficient statistics and result in noisy and unspecific spectra in the far-infrared region. [34] But even if this frequency range is analyzed properly and the vibrational modes giving the intermolecular interaction between anion and cation can be assigned correctly, another problem persists. It is unclear to what extent frequency positions and frequency shifts of intermolecular vibrational bands can be fully referred to changing force constants indicating stronger or weaker interaction between the a...

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“…[5][6][7][8][9] Despite the importance of the vapor pressures of the ionic liquids and the related thermodynamic properties of vaporization (enthalpies, entropies, and Gibbs energies of vaporization), most of the works performed until know were focused in estimate/determine the enthalpies of vaporization. 7,[10][11][12][13][14][15][16][17][18][19][20][21] The nature of the gas phase of ionic liquids is still in debate; however, the theory that the vaporization of ionic liquids occurs as a direct liquid to gas transfer of the intact ionic pair has been supported by several studies using photoionization, 22 line of sight mass spectrometry, 11,12,23 Fourier transform ion cyclotron resonance, 24,25 field ionization method, 26 tunable vacuum ultraviolet photoionization, 15 and more recently by molecular dynamics simulations. 27,28 Recently, we reported the thermodynamic study concerning the vaporization of the [C N-1 C 1 im][NTf 2 ] (N = 3-9, 11, and 13) ionic liquid series, where important trends for the enthalpies and entropies of vaporization were found, which are related to a change in the molecular structure of the liquid phase around [C 6 C 1 im][NTf 2 ].…”

Section: Introductionmentioning

confidence: 99%

Vapor pressures of 1,3-dialkylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids with long alkyl chains

Rocha

Coutinho

Santos

2014

The Journal of Chemical Physics

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4, 6, 8, 10, and 12). This effect is related with the predominant orientation of the terminal methyl group of the alkyl chain to the imidazolium ring and their influence in the cation-anion interaction. The same Critical Alkyl length at the hexyl, (C 6 C 1 and C 6 C 6 ) was found for both asymmetric and symmetric series indicating that the nanostructuration of the ionic liquids is related with alkyl chain length.

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Estimating Enthalpies of Vaporization of Imidazolium‐Based Ionic Liquids from Far‐Infrared Measurements

Cited by 71 publications

References 34 publications

Cation–Anion Interaction‐Directed Molecular Design Strategy for Mechanochromic Luminescence

Cation–Anion Interaction‐Directed Molecular Design Strategy for Mechanochromic Luminescence

Dissecting Anion–Cation Interaction Energies in Protic Ionic Liquids

Vapor pressures of 1,3-dialkylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids with long alkyl chains

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