| Autor: |
Franz J; Institute of Theoretical Chemistry, University of Vienna, Währinger Straße 17, A-1090 Vienna, Austria., Oelschlegel M; Institute of Inorganic Chemistry, University of Göttingen, Tammannstraße 4, D-37077 Göttingen, Germany., Zobel JP; Institute of Theoretical Chemistry, University of Vienna, Währinger Straße 17, A-1090 Vienna, Austria., Hua SA; Institute of Inorganic Chemistry, University of Göttingen, Tammannstraße 4, D-37077 Göttingen, Germany., Borter JH; Department of Dynamics at Surfaces, Max-Planck-Institute for Multidisciplinary Sciences, Am Faßberg 11, D-37077 Göttingen, Germany., Schmid L; Department of Chemistry, University of Basel, St.-Johanns-Ring 19, CH-4056 Basel, Switzerland., Morselli G; Department of Chemistry, University of Basel, St.-Johanns-Ring 19, CH-4056 Basel, Switzerland., Wenger OS; Department of Chemistry, University of Basel, St.-Johanns-Ring 19, CH-4056 Basel, Switzerland., Schwarzer D; Department of Dynamics at Surfaces, Max-Planck-Institute for Multidisciplinary Sciences, Am Faßberg 11, D-37077 Göttingen, Germany., Meyer F; Institute of Inorganic Chemistry, University of Göttingen, Tammannstraße 4, D-37077 Göttingen, Germany.; International Center for Advanced Studies of Energy Conversion (ICASEC), D-37077 Göttingen, Germany., González L; Institute of Theoretical Chemistry, University of Vienna, Währinger Straße 17, A-1090 Vienna, Austria.; Vienna Research Platform for Accelerating Photoreaction Discovery, University of Vienna, Währinger Straße 17, A-1090 Vienna, Austria. |
| Abstrakt: |
We report a rhenium diimine photosensitizer equipped with a peripheral disulfide unit on one of the bipyridine ligands, [Re(CO) 3 (bpy)( S-S bpy 4,4 )] + ( 1 + , bpy = 2,2'-bipyridine, S-S bpy 4,4 = [1,2]dithiino[3,4- c :6,5- c ']dipyridine), showing anti-Kasha luminescence. Steady-state and ultrafast time-resolved spectroscopies complemented by nonadiabatic dynamics simulations are used to disclose its excited-state dynamics. The calculations show that after intersystem crossing the complex evolves to two different triplet minima: a ( S-S bpy 4,4 )-ligand-centered excited state ( 3 LC) lying at lower energy and a metal-to-(bpy)-ligand charge transfer ( 3 MLCT) state at higher energy, with relative yields of 90% and 10%, respectively. The 3 LC state involves local excitation of the disulfide group into the antibonding σ* orbital, leading to significant elongation of the S-S bond. Intriguingly, it is the higher-lying 3 MLCT state, which is assigned to display luminescence with a lifetime of 270 ns: a signature of anti-Kasha behavior. This assignment is consistent with an energy barrier ≥ 0.6 eV or negligible electronic coupling, preventing reaction toward the 3 LC state after the population is trapped in the 3 MLCT state. This study represents a striking example on how elusive excited-state dynamics of transition-metal photosensitizers can be deciphered by synergistic experiments and state-of-the-art calculations. Disulfide functionalization lays the foundation of a new design strategy toward harnessing excess energy in a system for possible bimolecular electron or energy transfer reactivity. |
