Time-dependent density functional theory study on the electronic excited-state hydrogen bonding of the chromophore coumarin 153 in a room-temperature ionic liquid

Fluorescence quenching of coumarin 153 by hydroxyl-functionalized room temperature ionic liquids

Steady-state absorption and fluorescence as well as time-resolved fluorescence of coumarin 151 (C151) and coumarin 153 (C153) were measured in hydroxyl-functionalized ionic liquids ([HOEmim][BF4] and [HOEmim][N(CN)2]) and in nonhydroxyl-functionalized ionic liquids ([Emim][BF4] and [Emim][N(CN)2]). Both the steady-state fluorescence and time-resolved fluorescence observations reveal that hydroxyl-functionalized ionic liquid quenches the fluorescence of C153 while the nonhydroxyl-functionalized ionic liquid does not. We also measured the time-resolved fluorescence anisotropy of C151 and C153 in both [HOEmim][BF4] and [Emim][BF4]. It is found that the ratio of the rotational relaxation lifetime of C153 in [HOEmim][BF4] with respect to that in [Emim][BF4] is about 15% larger than that of C151 in [HOEmim][BF4] with respect to that in [Emim][BF4], indicating extra interaction between C153 and [HOEmim][BF4] exists except the effect of the viscosity of ionic liquid.

Sodium-ion electrolytes based on ionic liquids: a role of cation-anion hydrogen bonding

Recent success of the sodium-ion batteries fosters an academic interest for their investigation. Room-temperature ionic liquids (RTILs) constitute universal solvents providing non-volatility and non-flammability to electrolytes. In the present work, we consider four families of RTILs as prospective solvents for NaBF4 and NaNO3 with an inorganic salt concentration of 25 and 50 mol%. We propose a methodology to rate RTILs according to their solvation capability using parameters of the computed radial distribution functions. Hydrogen bonds between the cations and the anions of RTILs were found to indirectly favor sodium solvation, irrespective of the particular RTIL and its concentration. The best performance was recorded in the case of cholinium nitrate. The reported observations and correlations of ionic structures and properties offer important assistance to an emerging field of sodium-ion batteries. Graphical Abstract Sodium-ion electrolytes.

DFT STUDY OF SOME TRIVALENT d- AND f-BLOCK METAL ION COMPLEXES OF ALLOXAN

Density functional calculations have been employed to elucidate the structures of some six coordinated complexes of alloxan monohydrate with some d- and f-block metals. Alloxan monohydrate may exist in the mono-ionized or di-ionized form in its complexes, and both states were investigated. It is found that when the metal ion is coordinated to three bidentate ligands, the structures are nearly trigonal prismatic, but replacement of a bidendate ligand by two monovalent ligands changes the geometry to deformed octahedral. The metal-alloxanate bonding is largely ionic for the lanthanoids. The calculated vibrational frequencies are in agreement with the experimentally determined ones.

Spectroscopic investigations and hydrogen bond interactions of 8-aza analogues of xanthine, theophylline and caffeine: a theoretical study

The structure, spectral properties and the hydrogen bond interactions of 8-aza analogues of xanthine, theophylline and caffeine have been studied by using quantum chemical methods. The time-dependent density functional theory (TD-DFT) and the singly excited configuration interaction (CIS) methods are employed to optimize the excited state geometries of isolated 8-azaxanthine, 8-azatheophylline tautomers and 8-azacaffeine in both the gas and solvent phases. The solvent phase calculations are performed using the polarizable continuum model (PCM). The absorption and emission spectra are calculated using the time-dependent density functional theory (TD-DFT) method. The results from the TD-DFT calculations reveal that the excitation spectra are red shifted relative to absorption in aqueous medium. These changes in the transition energies are qualitatively comparable to the experimental data. The examination of molecular orbital reveals that the molecules with a small H→L energy gap possess maximum absorption and emission wavelength. The relative stability and hydrogen bonded interactions of mono and heptahydrated 8-azaxanthine, 8-azatheophylline tautomers and 8-azacaffeine have been studied using the density functional theory (DFT) and Møller Plesset perturbation theory (MP2) implementing the 6-311++G(d,p) basis set. The formation of strong N-H...O bond has resulted in the highest interaction energy among the monohydrates. Hydration does not show any significant impact on the stability of heptahydrated complexes. The atoms in molecule (AIM) and natural bonding orbital (NBO) analyses have been performed to elucidate the nature of the hydrogen bond interactions in these complexes.