Low Temperature Time-resolved FTIR Spectroelectrochemistry Technique And The Studies On Electron Transfer Mechanisms Of Ferrocenyl Derivatives

A briefly review for the method, experimental technique, application anddevelopment of in-situ FTIR spectroelectrochemistry (FTIRs) and IRspectroelectrochemical cell was carried out. A low temperature in-situ infraredreflected absorbance spectroelectrochemical (LT IRRAS) cell was designed andcharacterized. A series of ferrocenyl derivatives were designed, synthesized andcharacterized. A systematic investigation of the electron transfer (ET) behavior of thebisferrocenyl derivatives was undertaken via electrochemistry and in-situ FTIRs. Themechanism of electrochemical redox reactions of the bisferrocenyl derivatives and theeffects of conjugated group and molecular structure on the ET behavior of thebisferrocenyl derivatives were discussed. The research conclusions provide usefulinformation at molecular lever for molecular electronic devices, energy conversion,electron-transfer mediators and ion sensors. The dissertation focuses on the followingaspects:1. A low temperature in-situ infrared reflected absorbance spectroelectrochemical(LT IRRAS) cell was designed. It works very well in the temperature range from 173K to room temperature with temperature control precision within±0.5 K. Besides, itcan work, successively, for long time with filling the Dewar flask with liquid N₂. Theelectrochemical performance of the cell is characterized by cyclic voltammetry withK₄Fe(CN)₆ at room temperature and by steady-state voltammetry with ferrocene atlow temperature. The low temperature applicability of the cell for in situ FTIR isdemonstrated to observe the electrogenerated intermediate of1,4-bis(2-ferrocenylvinyl)benzene (p-(Fc-CH=CH)₂BZ).2. A series of ferrocenyl derivatives were designed and synthesized by Suzuki,Wittig and other reactions. The products were characterized with IR, MS, ¹H-NMRand ICP-AES.3. Electron transfer mechanisms and electron pass pathways of the bisferrocenyl derivatives were studied by cyclic voltammetry (CV), differential pulse voltammetry(DPV) and steady-state voltammetry. The effects of different substitutes onelectrochemical behaviour of ferrocenyl group were discussed. The results showedthat the electron transfer mechanisms of D-Ï€-D molecules LP 1, LP2, LP3, LP4, LP5,LP6 and LP7 are all two-consecutive one-electron processes. As the conjugatedgroups (bridge) between the two ferrocenyl moieties were various in the molecules,only LP2, LP4 and LP5 showed two pairs of distinguished redox waves involtammograms, due to the strong interacting between two redox centers in themolecules. As the mercury atom was an electron donor and there were repulsiveelectrostatic effect between mercury atom and iron atom, the electrochemicalbehaviors of mercury-bridged D-M-D molecules LP9 and LP10 were different fromthe D-Ï€-D molecules. Moreover, the voltammograms of LP9 show a single redox peakwhichâ–³E_p is between those of 1e and 2e reaction. It is suggested that the secondstep electron transfer is easier than the first.4. The electrochemical redox processes of bisferrocenyl derivatives were studiedby in-situ FTIR spectroelectrochemistry combined with rapid-scan time-resolvedFTIR, surface-enhanced infrared spectroscopy, two-dimensional infrared (2D-IR)correlation spectroscopy and digital simulation. The simulation of in-situ FTIRspectroelectrochemical behavior of LP1 under various temperatures was carried out,and several dynamical parameters were got according to the simulation. The in-situFTIR spectroelectrochemical behavior of LP2 was studied by surface-enhancedinfrared spectroscopy undertook on Au electrode electrodeposited wtih Pt nano-layers.2D-IR was employed to analyze the in-situ FTIR spectroelectrochemistry of LP3 andLP4. There were intermediate absorption bands at～1589 and 1604 cm^-1 in the in-situFTIR spectroelectrochemical redox processes of LP1 and LP2, respectively; andintermediate absorption bands at～2202 cm^-1 in the in-situ FTIRspectroelectrochemical redox processes of LP3 and LP4. The bands at 1589 and 1604cm^-1 were the absorption of benzene skeleton vibration due to the asymmetricpara-substituents. Because of the influences of para-substituents, molecular plane andconjugated properties, there were no considerable changes to the benzene skeleton vibration during the electrochemical processes of LP3, LP6 and LP7, therefore, therewere no intermediate absorption bands between～1590 to～1600 cm^-1. As the C≡Cstretch vibration modeν_C≡C in LP3 was sensitive toÏ€-electron changes of theconjugated system, herein the intermediate absorption bands at 2202 cm^-1 was visible.In the molecule of LP4, the C≡C—C≡C system was linear and can be taken as thesymmetric center of the molecule, moreover, there was considerable interactingamong the conjugatedÏ€-electron system of the whole molecule; hereby, theintermediate absorption bands at 2202 cm^-1 was visible.