Influence of the Protonatable Site in the Photo-Induced Proton-Coupled Electron Transfer between Rhenium(I) Polypyridyl Complexes and Hydroquinone

Abstract

In the present work the influence of the distance of the protonatable site of different ancillary ligands to the metal center on the luminescence quenching of Re I polypyridyl complexes by hydroquinone are evaluated by means of experimental and theoretical studies. In these systems, it is expected the occurrence of proton-coupled electron transfer (PCET) reactions upon excitation, which is a key process in solar-to-fuels energy conversion. The series fac-[Re(CO) 3 (2,2-bpy)(L)]PF 6 , L = pyridine, 1,4-pyrazine, 4,4'-bipyridyl, 1,2-bis-(4-pyridyl)ethane were synthesized and the luminescence quenching rate constant (k q ) by hydroquinone in CH 3 CN and 1:1 CH 3 CN/H 2 O were determined by steady-state and lifetime measurements. In bare acetonitrile, the 1,4-pyrazine exhibits the higher k q (3.49 ± 0.02) × 10 9 L mol -1 s -1 among the species investigated, followed by 4,4'-bipyridyl (k q = 2.50 ± 0.02) × 10 9 L mol -1 s -1. In 1:1 CH 3 CN/H 2 O, the k q values for all complexes are very similar evidencing the role of water molecules as proton acceptor following the reductive quenching of the complexes by hydroquinone. In CH 3 CN, the proton release for the solvent is not spontaneous and the higher basicity of the coordinated 1,4-pyrazine and 4,4'-bipyridyl in relation to 1,2-bis-(4-pyridyl)ethane after metal-to-ligand charge transfer (MLCT) excitation contributes to the proton transfer step. These results are corroborated by time-dependent density functional theory (TD-DFT) calculations. Moreover, the low H/D kinetic isotope effect (KIE) in 3:1 CH 3 CN/X 2 O (X = H or D) confirms that the major PCET pathway is the electron transfer followed by proton transfer, but for 1,4-pyrazine and 4,4'-bipyridyl the concerted proton-electron transfer seems to play a role at high hydroquinone concentrations.

New Cationic fac-[Re(CO)3(deeb)B2]+ Complex, Where B2 Is a Benzimidazole Derivative, as a Potential New Luminescent Dye for Proteins Separated by SDS-PAGE

“…Such intramolecular quenching has been previously reported through flash quench experiments of a ruthenium bipyridine complex ( Zhang et al, 2011 ; Nomrowski and Wenger, 2015 ; Lennox et al, 2017 ). The proton-coupled electron transfer has also been observed for rhenium(I) tricarbonyl complexes in intermolecular interactions ( Manbeck et al, 2016 ; Prado et al, 2016 ; Pannwitz and Wenger, 2019 ). The presence of the intramolecular hydrogen bond (IHB) in B2 could also be contributing to the relatively low quantum yield in the fac -[Re(CO) 3 ( deeb ) B2 ] + complex.…”

Phase‐Inversion Induced 3D Electrode for Direct Acidic Electroreduction CO2 to Formic acid

“…By contrast, at neutral pH, the lower proton concentration induces the electron transfer followed by proton transfer pathway. [29] Based on above, possible mechanism for formate/FA formation on TDPE-PPSU is proposed under neutral and acidic conditions (Equations (1-7)). At neutral pH, CO 2 is first adsorbed on the Bi surface, and accepts one electron to form CO 2 •−* (Equation 1).…”

Water-Induced Tuning of the Emission of Polyaniline LEDs within the NIR to Vis Range

“… 1 , 3 , 7 , 8 , 13 , 14 , 18 Such complex problems and systems are very often successfully examined with experimental and theoretical models, supported by computer simulations. 5 − 7 , 9 , 17 , 19 …”

“…1,3,7,8,13,14,18 Such complex problems and systems are very often successfully examined with experimental and theoretical models, supported by computer simulations. [5][6][7]9,17,19 A unique model material for studying some aspects of these processes by electroluminescence 20,21 is p-toluenesulfonic aciddoped polyaniline (PANI/PTSA). This is due to the presence of a conjugated π-electron system with relatively high electrical conductivity and an interacting with it coupled hydrogen bonding system, which can be modified by the presence of water molecules (Figure 3a).…”

“…Electron transfer, proton transfer, and excitation energy transfer from electrons to protons with excitation of the proton system are of great importance for key biological processes and modern advanced technological applications − as both intramolecular processes ,,,,,, and external, intermolecular, and intersystem ones. ,,− ,,, The last case is particularly interesting in connection to technical applications, ,, but they also have a crucial role in functioning biological systems at cellular and sub cellular levels. ,,,,,, Such complex problems and systems are very often successfully examined with experimental and theoretical models, supported by computer simulations. − ,,, …”