Electron Transfer of Manganese Halogenated Tetraphenylporphyrin Derivatives Assembled on Gold Electrodes

Abstract

Disulfide-linked manganese halogenated tetraphenylporphyrin derivatives separated by spacer methylene-chain groups (C n ), (MnPFPP−C n −S)2, (MnDCPP−C n −S)2, and (MnTTP−C n −S)2 [n = 2, 6, 12], were synthesized. The formation and redox response of self-assembled monolayers of these derivatives on a gold electrode were examined by electrochemistry combined with optical techniques in aqueous solution as well as in dimethyl sulfoxide (DMSO) solution. The self-assembly depended on the spacer methylene-chain length and the halogen species bound to the porphyrin. The fluorinated porphyrin with long methylene-chain length exhibited the largest surface concentration on the electrode. Electron transfer of the monolayers on the electrode was assumed to occur between Mn(III) and Mn(II) occluded in the porphyrin ring from results of cyclic voltammetry (CV) and potential modulation reflectance, that is, electroreflectance (ER) in DMSO and aqueous solutions. The ER could detect the electron transfer at higher sensitivities than CV especially in aqueous solution. The porphyrin with the longer methylene chain induced the larger positive shift of the formal potential in addition to the larger surface concentration of the porphyrins in the monolayer. The shift in the formal potential also depended on the halogen species in the order MnTTP−C n −S monolayer > MnDCPP−C n −S monolayer > MnPFPP−C n −S monolayer. Rate constants of the electron transfer from the monolayer to the electrode in DMSO and aqueous solutions, which can be calculated from the ER versus modulation frequency relation, increased with decreasing chain length and changed with the halogen species bound to the porphyrin in the order MnDCPP−C n −S monolayer > MnTTP−C n −S monolayer > MnPFPP−C n −S monolayer. The effect of the halogen species may be explained by steric hindrance against aggregation among the porphyrin units in the monolayers especially in aqueous solution.

Porphyrins as Active Components for Electrochemical and Photoelectrochemical Devices

“…The attenuation factor was estimated to be 0.07 Å −1 per methylene unit. 115 Instead, for unsaturated bridges, which are resonant with the metal Fermi energy, the electrons are injected directly into the chemical bonds of the molecular bridge and reach the electrode through a resonant transport (or hopping) mechanism. In this latter case, the distance dependence of the conductance is weak and small β values are typical of a resonant mechanism.…”

Electron transfer of quinone self-assembled monolayers on a gold electrode

“…The SAMs were formed on the gold electrode (50 nm of Au (1 1 1) on Ti-deposited smooth glass, Nippon Laser & Electronics Lab) by immersion in a solution of chloroform containing the quinone derivatives (50 mol dm −3 ) for 12 h, followed by carefully rinsing with chloroform [20,21]. Infrared reflectionabsorption spectroscopy (IR-RAS) measurements of the SAMs were performed with a PerkinElmer Spectrum 2000 FT-IR spectrometer.…”

TiO2 Photonic Crystal Sensitized with Mn3O4 Nanoparticles and Porphine Manganese(III) as Efficient Photoanode for Photoelectrochemical Water Splitting

“…31,33 Figure 4B shows that PMA demonstrates a strong absorbance at 480 nm, which can be assigned to charge transfer mixed with the π to π* transition of the PMA moiety, 34 and the weak absorbance in the range 560−800 nm is attributed to the Q-bands of the a 2u (π) → e g *(π) transition of PMA. 34,35 From Figure 4B, we can also see that the PMA/TPC electrode and the Mn 3 O 4 /PMA/TPC electrode exhibit the same two typical electronic absorptions to free PMA. However, the low energy Q-band with maxima at 650 nm of PMA in the composite shows a 28 nm red-shift with respect to that of free PMA, which is attributed to the strong electronic coupling and significant electronic interaction between the PMA moiety and TiO 2 .…”

“…However, the TPC electrode has higher diffuse reflection capabilities in the visible regions (from 400 to 800 nm) (Figure A), indicating that the incident light is significantly scattered within these macroporous TPC electrodes . The high light scattering of TPC will increase the light-harvesting efficiency. , The multireflection of the incident light in an air-filled pore of the TiO 2 matrix can effectively enhance the optical pathway. , Figure B shows that PMA demonstrates a strong absorbance at 480 nm, which can be assigned to charge transfer mixed with the π to π* transition of the PMA moiety, and the weak absorbance in the range 560–800 nm is attributed to the Q-bands of the a 2 u (π) → e g * (π) transition of PMA. , From Figure B, we can also see that the PMA/TPC electrode and the Mn 3 O 4 /PMA/TPC electrode exhibit the same two typical electronic absorptions to free PMA. However, the low energy Q-band with maxima at 650 nm of PMA in the composite shows a 28 nm red-shift with respect to that of free PMA, which is attributed to the strong electronic coupling and significant electronic interaction between the PMA moiety and TiO 2 .…”