Solvent effects

About: Solvent effects is a research topic. Over the lifetime, 17552 publications have been published within this topic receiving 436125 citations. The topic is also known as: solvent effect & solvent dependence.

A Mixed‐Solvent Strategy for Efficient Exfoliation of Inorganic Graphene Analogues

Abstract: Layered two-dimensional (2D) nanomaterials such as graphene are a conceptually new class of materials that offers new access to low-dimensional physics. Besides wellknown graphene, inorganic graphene analogues (IGAs) such as layered transition metal dichalcogenides (e.g., MoS2 and WS2) [5–7] and boron nitride (BN) have been attracting rapidly increasing attention in the past few years. These IGAs were expected to exhibit unique properties and have great potential in applications like transistors, energy storage, thermal conductors, and topological insulators. Moreover, IGAs like MoS2 and WS2 have intrinsic band gap and high mobility, and may even compete with graphene in certain fields. However, investigations on IGAs have been significantly hindered by the practical difficulties in the preparation and assembly of these 2D nanomaterials. Only a few approaches to obtain few-layered IGAs have been reported. Mechanical exfoliation was first used to obtain layered IGAs from their bulk materials. Other approaches that are being explored include chemical synthesis and liquid exfoliation. Coleman et al. recently reported a surfactant-free liquid-exfoliation method which can produce few-layered nanosheets of IGAs dispersed in various organic solvents. Thermodynamic analysis suggested that, because of the high surface energy of IGAs, the best solvents are likely to have high boiling points. Using nonvolatile solvents makes it difficult to process IGAs into devices, due to the difficulties in the removal of solvent and the occurrence of aggregation during the slow solvent evaporation. To date, liquid exfoliation of layered MoS2 and WS2 in volatile solvent has met with very limited success. Herein we demonstrate a versatile and scaleable mixedsolvent strategy for liquid exfoliation of IGAs, including WS2, MoS2, and BN, in volatile solvents. By choosing solvents with appropriate composition, highly stable IGA suspensions can be obtained in low-boiling solvent mixtures, which can then be easily used in further applications. The dispersion of nanomaterials in liquids can be partially predicted by the theory of Hansen solubility parameters (HSP), which is a semi-empirical correlation developed to explain dissolution behavior. Three HSP parameters are used to describe the character of a solvent or material: dD, dP, and dH, which are the dispersive, polar, and hydrogen-bonding solubility parameters, respectively. The dissolution process is one of adaptation between the HSP parameters of solvents and solutes. The HSP distance Ra is used to evaluate the level of adaptation [Eq. (1)].

Combined molecular mechanical and continuum solvent approach (MM-PBSA/GBSA) to predict ligand binding

Abstract: Significant progress has been achieved in computational methods to treat solvent effects in recent years. Among various techniques, the continuum solvent approach appears to be practically promising because it can be used to calculate reliable interaction and solvation energies in complex systems. A computational scanning mutagenesis method, one of such new approaches, has been recently developed. It combines the molecular mechanical and continuum solvent approaches and allows one to identify the `hotspots' in binding interfaces from a single trajectory of a wild type complex. Such techniques can be also used as a tool to optimize the interacting species for the binding, or as a ranking procedure in high throughput screening.

Photochemistry of Ru( bpy)32+. Solvent Effects

Abstract: The excited-state lifetime of the metal-to-ligand charge-transfer (MLCT) excited state or states of Ru(bpy)3Z+ has been measured in a series of solvents at a series of temperatures. The data can be fit to the equation r(T)-' = k + k"' exp (-(AE'/k,T)) where k is the sum of the radiative (k,) and nonradiative (k,,) rate constants for decay of the MLCT state(s) and the temperature-dependent term involves a thermally activated transition from the MLCT state to a low-lying state or states presumably d-d in character. From a combination of lifetime and emission quantum yield measurements, values for k, and k,, have been obtained in the series of solvents. From the variations of the various kinetic parameters with solvent the following conclusions can be reached: (1) k, is only slightly solvent dependent; (2) the variations in k,, and emission energy with solvent are in quantitative agreement with the predictions of the energy gap law for radiationless transitions; and (3) the solvent dependence of the kinetic parameters k'O and AE', which characterize the MLCT - dd transition, can be considered in the context of electron-transfer theory including the observation of a linear relationship between In k'O and AE'(Barc1ay-Butter plot). In a final section the implications of solvent effects on the use of Ru(bpy)32+* as a sensitizer are discussed. We have shown that the energy gap law can be applied to nonradiative decay in a series of polypyridyl complexes of OS(II).'~~ The studies were based on the metal-to-ligand charge-transfer (MLCT) excited states of the two series of complexes (phen)- OSI*L,~+ and (bpy)OsL42+ (bpy is 2,2'-bipyridine, phen is 1,lO- phenanthroline; L = '/2bpy, 1/2phen, pyridine, PR,, Me2S0, CH,CN, ...). The nature of the experiment was to show from excited-state lifetime and emission measurements that plots of In k,, vs. E,, are linear where k,, is the nonradiative decay rate constant and E,, the emission energy. In addition, it was possible to account for the origin of the solvent dependence of k,, on the basis of the energy gap law using the series of Os-phen based MLCT excited states., In these studies, radiative rate constants, k,, for excited-state decay, were shown to be relatively insensitive to variations either in complex or in solvent. The earlier studies based on the Os(I1) complexes are part of a larger effort to explore in detail the photochemical and pho- tophysical properties of MLCT excited states. In many ways the "parent" compound associated with MLCT excited states is Ru- (b~y),~+. The excited-state electronic structures of R~(bpy),~+ and related complexes have been investigated by spectroscopic studie~,~ low-temperature emission and lifetime measurement^,^