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Ruthenium polypyridyl complexes have gained significant interest as photochemotherapies (PCTs) where their excited-state properties play a critical role in the photo-cytotoxicity mechanism and efficacy. Herein we report a systematic electrochemical, spectrochemical, and photophysical analysis of a series of ruthenium( ii ) polypyridyl complexes of the type [Ru(bpy) 2 (N–N)] 2+ (where bpy = 2,2′-bipyridine; N–N is a bidentate polypyridyl ligand) designed to mimic PCTs. In this series, the N–N ligand was modified through increased conjugation and/or incorporation of electronegative heteroatoms to shift the metal-to-ligand charge-transfer (MLCT) absorptions near the therapeutic window for PCTs (600–1100 nm) while incorporating steric bulk to trigger photoinduced ligand dissociation. The lowest energy MLCT absorptions were red-shifted from λ max = 454 nm to 564 nm, with emission energies decreasing from λ max = 620 nm to 850 nm. Photoinduced ligand ejection and temperature-dependent emission studies revealed an important interplay between red-shifting MLCT absorptions and accessing the dissociative 3 dd* states, with energy barriers between the 3 MLCT* and 3 dd* states ranging from 850 cm −1 to 2580 cm −1 for the complexes measured. This work demonstrates the importance of understanding both the MLCT manifold and 3 dd* state energy levels in the future design of ligands and complexes for PCT.
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This content will become publicly available on July 29, 2025
Picosecond Metal-to-Ligand Charge-Transfer Deactivation in Co(ppy) 3 via Jahn–Teller Distortion
The excited-state dynamics of fac-Co(ppy)3, where ppy = 2-[2-(pyridyl)phenyl], are measured with femtosecond UV-Vis transient absorption spectroscopy. The initial state is confirmed with spectroelectrochemistry to have significant metal-to-ligand charge transfer (MLCT) character, unlike other Co complexes that generally have ligand-to-metal charge transfer or ligand-field transitions in this energy range. Ground-state recovery occurs in 8.65 ps in dichloromethane. Density functional theory (DFT) calculations show that the MLCT state undergoes Jahn-Teller distortion and converts to a 5-coordinate 3MC state in which one Co-N bond is broken. The results highlights a potential pitfall of heteroleptic-bidentate ligands when designing strong-field ligands for transition metal chromophores.
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- Award ID(s):
- 2102376
- PAR ID:
- 10534042
- Publisher / Repository:
- Inorganic Chemistry
- Date Published:
- Journal Name:
- Inorganic Chemistry
- Volume:
- 63
- Issue:
- 30
- ISSN:
- 0020-1669
- Page Range / eLocation ID:
- 13825 to 13830
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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