物理化学学报2019，Vol.35Issue(6)：624-629,6.DOI:10.3866/PKU.WHXB201807035
偶氮苯基型离子液体溶液对空气中湿度的变色响应
Moisture-Responsive Behavior in the Azophenolic Ionic Liquid Solution Accompanied by a Naked-Eye Color Change
摘要
Abstract
Room temperature ionic liquids (ILs) that can exhibit a colorimetric response to moisture in the air are rarely reported in the literature.In this study,an azophenolic IL solution exhibited a spontaneous a colorimetric response,driven by the formation of hydrogen bonding between the [PhN=NPhO] anion and moisture in the air.This phenomenon was clearly understood using ultraviolet-visible (UV-Vis)absorption spectroscopy,nuclear magnetic resonance (NMR) spectra,experimental data,and theoretical calculations.Specifically,in the UV-Vis absorption spectra,absorption around 455 nm decreased,while the band around 343 nm increased in the IL CHCl3 solution as time progressed;this was accompanied by a color change from orange to faint yellow.This spontaneous,self-responsive process was further observed using 1H NMR data.When the IL solution was placed with sufficient time,all the 1H NMR peaks of the azophenolic anion shifted downfield,but no new signals appeared in the upfield region.The reason for this was easily identified as the stimuli in the air,such as CO2 and moisture.When pure CO2 was bubbled through the IL CHCl3 solution,the solution color changed from its original orange to light orange,but could not change further to faint yellow,which ruled out CO2 gas as a stimulus.When a small amount of water was gradually added to the IL solution (MeCN solvent),the absorption band around 474 nm decreased,coupled with an increase in the absorption band around 347 nm.This was accompanied by a color change from orange to faint yellow,which was almost identical to the self-responsive process in CHCl3 and CCl4.Moreover,two cuvettes of IL CHCl3 solution were placed under relative humidities of 28％ and 100％,respectively;the IL CHCl3 solution required a much longer time to exhibit a complete color change from orange to faint yellow under a lower relative humidity,demonstrating that moisture is the most likely stimulus triggering the self-responsive color change of the IL solution.As revealed by the Gaussian 09 program at the B3LYP/6-31++G(p,d) level,the distance between the oxygen atom on the azophenolic anion and the hydrogen atom on the H2O molecule was 0.174 nm,and the corresponding angle was 171.12°.Furthermore,the atomic dipole moment corrected Hirshfeld (ADCH) charge of the oxygen atom on the azophenolic anion was-0.52,and it increased to-0.62 after the azophenolic anion interacted with the H2O.Reduced density gradient analysis revealed that the spike corresponding to O…H-O for the IL-H2O complex was located at around-0.04 a.u..All the above data indicate that the presence of hydrogen bonding rendered the IL solution responsive to the moisture stimulus,and this response was accompanied by a color change that was visible to the naked eye.To the best of our knowledge,this is the first demonstration of a colorimetric change in an IL solution in response to moisture.We hope this work can help us to gain insight into some seemingly abnormal phenomena that occur during the research process.关键词
刺激响应/湿度/比色变化/氢键/离子液体溶液Key words
Stimuli-responsive/Moisture/Colorimetric change/Hydrogen bonding/lonic liquid solution分类
化学化工引用本文复制引用
潘明光,赵永升,曾小勤,邹建新..偶氮苯基型离子液体溶液对空气中湿度的变色响应[J].物理化学学报,2019,35(6):624-629,6.基金项目
The project was supported by the China Postdoctoral Science Foundation (2017M621476,2017M621477) and National Natural Science Foundation of China(51771112).中国博士后基金(2017M621476,2017M621477)和国家自然科学基金(51771112)资助项目 （2017M621476,2017M621477）
