Physical Properties and Low-Frequency Polarizability Anisotropy and Dipole Responses of Phosphonium Bis(fluorosulfonyl)amide Ionic Liquids with Pentyl, Ethoxyethyl, or 2-(Ethylthio)ethyl Group
Physical Properties and Low-Frequency Polarizability Anisotropy and Dipole Responses of Phosphonium Bis(fluorosulfonyl)amide Ionic Liquids with Pentyl, Ethoxyethyl, or 2-(Ethylthio)ethyl Group
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DOI：
10.1021/acs.jpcb.2c07466
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发表时间：
2023-01-05
影响因子：
3.3
通讯作者：
Shirota, Hideaki
中科院分区：
文献类型：
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作者：
Ando, Masatoshi;Ohta, Kaoru;Shirota, Hideaki
本研究比较了三种合成离子液体（ILs）的物理性质，如玻璃化转变温度、熔点、粘度、密度、表面张力、电导率等，以及在200 cm-1下的低频光谱，即三乙基戊基磷二（氟磺酰基）酰胺（[P2225][NF2]）、乙氧基乙基三乙基磷二（氟磺酰基）酰胺（[P222(2O2)][NF2]）和三乙基[2-（乙基硫）乙基]磷二（氟磺酰基）酰胺（[P222(2S2)][NF2]）。在不同温度下使用飞秒拉曼诱导克尔效应光谱（fs-RIKES）和太赫兹时域光谱（THzTDS）。[P222(2S2)][NF2]的粘度和玻璃化转变温度最高，而[P222(2O2)][NF2]的粘度和玻璃化转变温度最低。其中[P222(2S2)][NF2]具有最高的密度和表面张力，[P222(2O2)][NF2]具有最高的导电性。三种il的RIKES和THz-TDS谱线形状变化显著。对于[P2225][NF2]，分子动力学模拟成功地再现了实验光谱的线形，并表明RIKES谱主要是由于阳离子和交叉项及其旋转运动，而THz-TDS谱主要是由于阴离子及其平动运动。这表明，利用fs-RIKES和THz-TDS方法来揭示分子在低频域的运动是可取的。与[P2225][NF2]和[P222(2O2)][NF2]相比，[P222(2S2)][NF2]在fs-RIKES和THz-TDS的低频谱中具有更高的频率峰和更宽的频带。
This study compared the physical properties, e.g., glass transition temperature, melting point, viscosity, density, surface tension, and electrical conductivity, and the low-frequency spectra under 200 cm-1 of three synthesized ionic liquids (ILs), triethylpentylphosphonium bis(fluorosulfonyl)amide ([P2225][NF2]), ethoxyethyltriethylphosphonium bis(fluorosulfonyl)amide ([P222(2O2)][NF2]), and triethyl[2-(ethylthio)ethyl]phosphonium bis(fluorosulfonyl)amide ([P222(2S2)][NF2]), at various temperatures using femtosecond Raman-induced Kerr effect spectroscopy (fs-RIKES) and terahertz time-domain spectroscopy (THzTDS). The [P222(2S2)][NF2] had the highest viscosity and glass transition temperature, whereas the [P222(2O2)][NF2] had the lowest. Among the three ILs, the [P222(2S2)][NF2] had the highest density and surface tension, and the [P222(2O2)][NF2] had the highest electrical conductivity. The RIKES and THz-TDS spectral line shapes for the three ILs varied significantly. For the [P2225][NF2], molecular dynamics simulations successfully reproduced the line shapes of the experimental spectra and indicated that the RIKES spectrum was mainly due to the cation and cross-term and their rotational motions, whereas the THz-TDS spectrum was mainly due to the anion and its translational motion. This shows that it is desirable to utilize both fs-RIKES and THz-TDS methods to reveal molecular motions at the low-frequency domain. The [P222(2S2)][NF2] had higher frequency peaks and broader bands in the low-frequency spectra via fs-RIKES and THz-TDS than those for the [P2225][NF2] and [P222(2O2)][NF2].