This study investigates the impact of structural isomerism on the excited state lifetime and redox energetics of heteroleptic [Ir(ppy)2(bpy)]+ and homoleptic Ir(ppy)3 photoredox catalysts using ground-state and time-dependent density functional theory methods. While the ground- and excited-state reduction potentials differ only slightly among the isomers of these complexes, our findings reveal significant variations in the radiative and non-radiative decay rates of the reactivity-controlling triplet 3MLCT states of these closely related species. The observed differences in radiative decay rates could be traced back to variations in the transition dipole moment, vertical energy gaps, and spin–orbit coupling of the isomers. In [Ir(ppy)2(bpy)]+, transition dipole moment differences play a significant role in controlling the relative lifetime of the triplet states, which we rationalized by a vectorial analysis of permanent dipole moments of the ground and excited states. Regarding the two isomers of Ir(ppy)3, changes in radiative decay rates were primarily attributed to variations in vertical energy gaps and intensity borrowing from other singlet-singlet transitions driven by spin–orbit coupling. Non-radiative decay variations were assessed in terms of differences in reorganization energies, adiabatic energy gap, and spin–orbit coupling. For both complexes, reorganization energies associated with low-energy molecular vibrations and metal–ligand bond length changes following the de-excitation process were major contributors. These insights provide a deeper understanding of how molecular design can be leveraged to optimize the performance of iridium-based photoredox catalysts, potentially guiding the development of more efficient catalytic systems for future applications.
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14 January 2025
Research Article|
January 14 2025
A computational study on the effect of structural isomerism on the excited state lifetime and redox energetics of archetype iridium photoredox catalyst platforms [Ir(ppy)2(bpy)]+ and Ir(ppy)3
Daniel Gómez Bustos
;
Daniel Gómez Bustos
(Conceptualization, Investigation, Methodology, Writing – original draft, Writing – review & editing)
Department of Chemistry and Biochemistry, University of Texas at El Paso
, El Paso, Texas 79968, USA
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Sreeprasad Sreenivasan
;
Sreeprasad Sreenivasan
(Supervision)
Department of Chemistry and Biochemistry, University of Texas at El Paso
, El Paso, Texas 79968, USA
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Balazs Pinter
Balazs Pinter
a)
(Conceptualization, Supervision, Writing – original draft, Writing – review & editing)
Department of Chemistry and Biochemistry, University of Texas at El Paso
, El Paso, Texas 79968, USA
a)Present address: European Research Council Executive Agency, Brussels, Belgium. Author to whom correspondence should be addressed: [email protected]
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a)Present address: European Research Council Executive Agency, Brussels, Belgium. Author to whom correspondence should be addressed: [email protected]
J. Chem. Phys. 162, 024306 (2025)
Article history
Received:
September 18 2024
Accepted:
December 19 2024
Citation
Daniel Gómez Bustos, Sreeprasad Sreenivasan, Balazs Pinter; A computational study on the effect of structural isomerism on the excited state lifetime and redox energetics of archetype iridium photoredox catalyst platforms [Ir(ppy)2(bpy)]+ and Ir(ppy)3. J. Chem. Phys. 14 January 2025; 162 (2): 024306. https://doi.org/10.1063/5.0239293
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