Electrochemical And Surface-enhanced Raman Spectroscopy Studies On Properties Of Oligo(1,4-phenylene Ethynylene)S Anthraquinone Molecular Wires On Gold Electrode

Quinone species are widely found in living organism and are attractive for the preparation of molecular devices and switches. In particular, quinone derivatives are important to understand the coupling of proton and electron transfer which are at the core of numerous natural and artificial systems in chemistry and biology. SERS is considered as a noninvasive technology with very high sensitivity by which one can get high-quality characteristic signal of adsorbed molecule through avoid the interference of the same species in the solution phase effectively, thus it has been widely used in chemistry, catalysis, physics, materials science, biology chemistry, energy and many other fields.To understand the coupling of proton and electron transfer, electrochemical surface-enhanced Raman spectroscopy (EC-SERS), combined with cyclic voltammetry, and the density functional theoretical (DFT) method were used to investigate self-assembledmonolayer (SAM) adsorption and reduction processes of anthraquinone derivatives in buffered, unbuffered aqueous solution and ionic liquids.The main contents and results are as below:1. Aiming to deeply understand the redox reaction of quinone, in both buffered and unbuffered aqueous solution at different pH’s, we carried out an in situ electrochemical surface-enhanced Raman spectroscopic (EC-SERS) study to characterize 2-(thiolphenylene ethynylene) anthraquinone molecular wires (2-AQ) various surface species in different electrode potential regions on gold electrodes. A further analysis with DFT calculation reveals that the redox reaction of anthraquinones in buffered water is well described as a two-electron two-proton reduction to make the hydroquinone, while an overall reaction in unbuffered water is main a complex reduction to make an mixture of protonation states and quinone dianion, implying that intermolecular hydrogen-bonding plays an important role in making quinones a 2 e- redox couple in aqueous solution.2. To deeply understand the redox mechanism of quinone, we carried out an in situ EC-SERS study to characterize the redox behavior of 2-(thiolphenylene ethynylene) anthraquinone molecular wires (2-AQ) in ionic liquids. The results of CV and EC-SERS measurements as well as DFT calculations indicate clearly that its redox reaction undergoes (1) two chemically reversible one-electron reduction to make AQ·- and 2-AQ2-, respectively, in ionic liquids (BMIMPF6); (2) an overall reaction in ionic liquids with the addition of water, is as a two-electron reduction to produce an mixture of protonation states and quinone dianion. The results show that intermolecular hydrogen-bonding plays a crucial important role in the redox behavior of quinone and its derivates.3. We have studied the reduction reaction of 1-(thiolphenylene ethynylene) anthraquinone molecular wires (1-AQ) by cyclic voltammetry and EC-SERS. The results indicate that, the C=O reacts with the C=C in the molecular structure of 1-AQ and form a pyran ring under acidic conditions.4. With the high sensitivity of SERS, we have studied the photoinduced coupling reaction of aminothiophenol derivatives on metal substrate. The results indicate that the coupling reactions could happen only there is a good conjugation effect between the amino and the molecule.