Study Of The Microenvironment Effects On TCNQ With Spectrum Technology

The changing of microenvironment, such as different solvents, different pH and alterative electric/magnetic field, has various effects on the physical, chemical or biologic phenomena that we are interested in, even leading to different results. It is quite important to investigate the microenvironment effects so as to improving the study of Physics, Chemistry and biology.TCNQ has been in the center of people's attention since it was discovered in 1958 because of its favorable optical and electrical properties, especially its capability of forming various polymer films with different metals or compounds which have quite a lot of potential applications. Although most of the investigations about TCNQ are taken in solutions or in electric/magnetic field, the microenvironment effects on TCNQ has not been discussed in organized set, and the effects of different solvents on the molecular vibration and the energy level transition of TCNQ has even never been reported before. In this article, with the help of infrared spectrum technology, UV-vis spectrum technology and spectroelectrochemistry technology, we study how the changing of microenvironment infects the molecular structure, vibrational frequency and energy level transition of TCNQ.1, through changing the kind of solvents, we investigate the solvent effects on the C≡N vibrational frequency using the technology of infrared spectrum. We record the infrared spectra of TCNQ in five different solvents and find out that the C≡N vibrational frequency is decreasing along with the increasing of the AN of the solvents after careful analysis. The conclusion is explained using the accept-donor model as following: C≡N has lone pair electrons, which is easy to give out. The more the solvent is"attractive"to electrons (means that the bigger the AN is), the stronger the interaction between C≡N and the solvent is. Then the combine of them is more stable, which makes the energy of C≡N smaller and the vibrational frequency lower. So in the infrared spectra the wave number of C≡N get smaller when the AN get bigger. It is obvious that the accept-donor model which use the AN and DN of solvents to explain the changing of vibrational frequency is a simple, convenience half-experienced model. Because of its simple linear relationship with the move of frequency, it is very helpful to explain and forecast the changing of vibrational frequency.Besides, utilizing the Linear Solvation Energy Relationship, we carry out linear least-squares fitting on the parametersπ^*,δ,α,βand build the LSER equation of TCNQ:υ=2242.8-35.6π^*-5.9βAnd through the analysis of the LSER equation, we conclude that the effect of solvent on C≡N vibrational frequency is coming from the combine of the acceptor and donor but not from the H bond.2, with the help of UV-vis spectrum technology, we study the solvatochromism phenomenon of TCNQ. The absorption band of the UV-vis region is moving due to the effect of different solvents on the electronic energy levels. we record the UV-vis spectra of TCNQ in five different solvents for investigation.Through the experiment, we find out that the absorption band of TCNQ around 400nm move to the shortwave region during the solvent polarity parameters E^T_N,ET(30)get bigger, which means the solvent polarity increases. And also the peak values of the absorption bands have good linear relationship with the value of the solvent polarity parameters. Via calculation we know that the absorption band of TCNQ around 400nm is due to the transition ofπ→π* and the energy of the transition is about 3.10eV. In the molecular orbit model, the transition is because of the co-work of the orbital transition of B_3g→B_1u and B_3g→Au.The increasing of solvent polarity induces the absorption band of TCNQ to carry through a increasing blue shift, which we call as negative solvatochromism. So we deduce that during the increasing of solvent polarity, the LUMO and LUMO+1 energy levels are getting higher at the same time as the HOMO and HOMO-1 energy levels are getting lower. Also, we could know that the dipole moment of the ground state is larger than that of the excited state (μg>μe).By comparing of the linear fitting results, we conclude that the molecular probes which are similar with the solute in structure are better in describing the solvent polarity than the physical parameter we usually employ.3, we develop a spectroelectrochemistral thin cell which could use in both the UV and Raman detective all by ourselves to realize our experimental tentative plan. We employ an optically transparent Pt minigrid electrode as the working electrode, a Pt plate as the counter electrode and the 217 saturated calomel electrode as the reference electrode to build up the three- electrode system. When design the thin cell, we overall consider the Optical routes of UV and Raman spectrographs, the impedance effect and the edge effect.Using the cyclic vonammetry test we represent the thin cell. We could see that the oxidation and reduction peaks are in good symmetry; the voltaic ratio of the oxidation and reduction peaks is nearly 1; the current go back to the basic line after getting to the maximum. All of the above prove that the thin cell has restrained the impedance effect and the edge effect, and works quite well to meet the requirements of electrospectrochemistral experiments.4, using our self-made spectroelectrochemistral thin cell, with the help of UV-vis spectrum technology, we research the electrochromism phenomenon of TCNQ. In the electric field, the neutral TCNQ turns into TCNQ^-, and then go on turning into TCNQ^2-, which is not able to last long but will turn to DCTC^- in the present of oxygen. This series of changing could be reflected in the UV spectrum and we also could tell that from the color's changing of the solution.In the spectrogram we could see that the absorption band around 400nm decreases until disappear, which means the TCNQ and TCNQ- surrounding the working electrode are reducing till they are totally converted to TCNQ^2-; the characteristic absorption band of TCNQ^2- around 330nm increases means that the TCNQ^2- surrounding the working electrode are getting more and more; the characteristic absorption band of DCTC- around 488nm is also increasing after the 330nm absorption band's increasing is visible, which means the TCNQ^2- are turning into DCTC- in the present of oxygen. The continuous absorption band from 700nm to 900nm are increasing at first and decreasing after a while, which implies the TCNQ turns into TCNQ- after get an electron at first, and along with the durative current, the TCNQ- turns into TCNQ^2- after a while.The color of the solution also turns from dark green to saffron yellow while the current goes on. We can tell that TCNQ has the character of electrochromism.In this paper, we investigate the solvent effects, solvatochromism and electrochromism characters of TCNQ through the technologies of molecular spectrum and spectroelectrochemistry. This work must have some referenced value for the study of TCNQ.