Impact of peripheral ligand modification on MLCT stability and optical properties of Ru(II) complexes for potential photocatalytic application
DOI:
https://doi.org/10.65419/albahit.v5i1.118Keywords:
Ru(II) complexes, Photochemical degradation, tbbpy and dppz ligands, pseudo-first-order kinetics, Apparent rate constant, solvent effects, MLCTAbstract
This study investigates the role of peripheral ligand modification in controlling the MLCT energetics and photochemical stability of Ru(II) polypyridyl complexes, using tbbpy- and dppz-based systems as a comparative platform. By combining ¹H NMR spectroscopy, steady-state UV–Vis absorption, and time-dependent photochemical kinetics, we demonstrate that peripheral ligands act as electronically active components rather than passive structural substituents.
A key finding of this work is the spectral invariance of the Ru–tbbpy complex in both aprotic (CH₃CN) and protic (CH₃OH) solvents, which provides a rare baseline for isolating solvent-driven photochemical pathways. In contrast, incorporation of the π-extended dppz ligand induces a systematic increase in the MLCT energy gap and markedly enhances photochemical robustness under continuous irradiation. Kinetic analysis in methanol reveals pseudo-first-order behavior for the tbbpy system, with an apparent rate constant of (3.3 ± 0.2) × 10⁻³ min⁻¹ and a half-life of approximately 210 min.
The emergence of new ligand-centered absorption bands upon irradiation indicates photo-induced transformation into stable photoproducts rather than nonspecific decomposition. These results highlight peripheral ligand design as an effective strategy for modulating MLCT stability and improving the durability of Ru(II)-based photosensitizers, offering mechanistic insights relevant to the rational development of photoactive coordination complexes.
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