Bifurcation of Excited-State Population Leads to Anti-Kasha Luminescence in a Disulfide-Decorated Organometallic Rhenium Photosensitizer

Author(s)

Julia Franz, Manuel Oelschlegel, J. Patrick Zobel, Shao An Hua, Jan Hendrik Borter, Lucius Schmid, Giacomo Morselli, Oliver S. Wenger, Dirk Schwarzer, Franc Meyer, Leticia González

Abstract

We report a rhenium diimine photosensitizer equipped with a peripheral disulfide unit on one of the bipyridine ligands, [Re(CO)₃(bpy)(^S-Sbpy^4,4)]⁺ (1⁺, bpy = 2,2′-bipyridine, ^S-Sbpy^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-Sbpy^4,4)-ligand-centered excited state (³LC) lying at lower energy and a metal-to-(bpy)-ligand charge transfer (³MLCT) state at higher energy, with relative yields of 90% and 10%, respectively. The ³LC 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 ³MLCT 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 ³LC state after the population is trapped in the ³MLCT 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.

Organisation(s)

Department of Theoretical Chemistry, Research Platform Accelerating Photoreaction Discovery

External organisation(s)

Georg-August-Universität Göttingen, Max Planck Institute for Natural Sciences, Universität Basel

Journal

Journal of the American Chemical Society

ISSN

0002-7863

DOI

https://doi.org/10.1021/jacs.4c00548

Publication date

2024

Peer reviewed

Yes

Austrian Fields of Science 2012

104016 Photochemistry, 104017 Physical chemistry, 106002 Biochemistry

ASJC Scopus subject areas

Catalysis, Chemistry(all), Biochemistry, Colloid and Surface Chemistry

Portal url

https://ucris.univie.ac.at/portal/en/publications/bifurcation-of-excitedstate-population-leads-to-antikasha-luminescence-in-a-disulfidedecorated-organometallic-rhenium-photosensitizer(d0fbc6a6-4766-45c1-b1ed-2ec850ee3b71).html