Dielectric relaxation and ultrafast transient absorption spectroscopy of [C6mim]+[Tf2N]−/acetonitrile mixtures.
Dielectric relaxation and ultrafast transient absorption spectroscopy of [C6mim]+[Tf2N]−/acetonitrile mixtures.
复制标题
DOI：
10.1039/c2cp23704k
复制
发表时间：
2012-02
期刊：
影响因子：
--
通讯作者：
P. W. Lohse;N. Bartels;A. Stoppa;R. Buchner;T. Lenzer;K. Oum
中科院分区：
文献类型：
--
作者：
P. W. Lohse;N. Bartels;A. Stoppa;R. Buchner;T. Lenzer;K. Oum
用介电弛豫光谱（DRS）和超快瞬态吸收技术研究了离子液体[C（6）mim]（+）[Tf（2）N]（-）和乙腈的混合体系，并以12 '-脱辅基-β-胡萝卜素-12'-酸（12'CA）为探针.还记录了12'CA分子的稳态吸收光谱。探针的S（0）→ S（2）吸收最大值的位置与混合物的极化率线性相关，表明整体组成是局部组成的良好近似。12'CA的S（1）/ICT态的寿命τ（1）随组成在纯乙腈（42 ps）和纯[C（6）mim]（+）[Tf（2）N]（-）（94 ps）之间相当平稳地变化。在低IL含量似乎是离散离子对的影响。采用静态介电常数从DRS实验中，人们发现，在IL混合物中的探针的寿命短于在具有相同极性参数的纯有机溶剂。这表明在含IL的混合物中S（1）/ICT状态的稳定性增加，最可能是由于阳离子和探针偶极的负端之间的IL特异性库仑相互作用。观察到一个超快溶剂化成分，这是ca。0.5 ps的纯乙腈中，并接近纯IL的值（2.0 ps）已经约x（IL）= 0.3。这是解释在一个有效的干扰乙腈的合作溶剂化反应的存在下，少量的IL和可能的粘度增加时，加入IL。加入少量从DRS实验中提取的IL后，乙腈的平均纵向弛豫时间增加，也支持这一观点。
Mixtures of the ionic liquid (IL) [C(6)mim](+)[Tf(2)N](-) and acetonitrile have been investigated by a combination of dielectric relaxation spectroscopy (DRS) and ultrafast transient absorption techniques using the molecular probe 12'-apo-β-carotenoic-12'-acid (12'CA). Steady-state absorption spectra of the 12'CA molecule have also been recorded. The position of the probe's S(0)→ S(2) absorption maximum correlates linearly with the polarizability of the mixture, suggesting that the bulk composition is a good approximation to the local composition. The lifetime τ(1) of the S(1)/ICT state of 12'CA varies rather smoothly with composition between the value for pure acetonitrile (42 ps) and neat [C(6)mim](+)[Tf(2)N](-) (94 ps). At low IL contents there appears to be an influence of discrete ion pairs. Employing static dielectric constants from the DRS experiments, one finds that the lifetime of the probe in the IL mixtures is shorter than that in pure organic solvents with the same polarity parameter. This suggests an increased stabilization of the S(1)/ICT state in IL-containing mixtures, most likely due to IL-specific Coulombic interactions between the cation and the negative end of the probe's dipole. An ultrafast solvation component is observed which is ca. 0.5 ps in pure acetonitrile, and approaches the value for the pure IL (2.0 ps) already around x(IL) = 0.3. This is interpreted in terms of an efficient perturbation of the cooperative solvation response of acetonitrile by the presence of small amounts of IL and possibly also the viscosity increase when adding IL. This view is also supported by the increase of the average longitudinal relaxation time of acetonitrile upon addition of small IL amounts extracted from the DRS experiments.