Ultrafast transient absorption spectroscopy was employed to investigate the excited state dynamics of the iron(II)-cobalt(III) dyad [Fe-BL-Co] following excitation at 515 nm. Measurements were conducted on 10 mM solutions in acetonitrile to avoid dissociation effects. The transient spectra revealed a complex relaxation cascade initiated by population of hot singlet and triplet metal-to-ligand charge transfer (MLCT) states. A fast decay component, shorter than the instrument response function (IRF ≈ 0.12 ps), was observed, consistent with internal conversion from a hot 1MLCT* state to a vibrationally relaxed 3MLCT* manifold within tens of femtoseconds. This is followed by a rapid thermalization process characterized by a time constant of 140 fs (2), corresponding to equilibration within the 3MLCT energy landscape.
The most prominent feature in the data is the long-lived 3MLCT state, which exhibits a lifetime of 19.8 ps—significantly longer than the 17.1 ps observed for the isolated photosensitizer [Fe-BL]. This extension is attributed to stabilization of the charge-transfer state through electronic coupling with the cobalt center, confirmed by both experimental redshifts in the MLCT band and DFT calculations showing a reduced HOMO-LUMO gap. The decay associated spectra (DAS) obtained via global fitting reveal four distinct kinetic components: DAS₁ (
Notably, the spectral evolution in the red region (>520 nm) differs significantly between [Fe-BL] and [Fe-BL-Co].SH3BGRL Antibody MedChemExpress In the dyad, the ground state bleach (GSB) shifts to longer wavelengths by ~30–40 nm, accompanied by a pronounced increase in the amplitude and broadening of the excited state absorption (ESA) signal. This redshift corresponds to a ~0.17 eV decrease in the effective bandgap, in excellent agreement with the DFT-predicted reduction in the HOMO-LUMO gap.PMID:34978098 Furthermore, the kinetics around 400 nm exhibit mixed behavior: amplitudes rise above zero before decaying below it, suggesting a contribution from both GSB and ESA features, possibly arising from vibrational relaxation or secondary charge redistribution.
Despite the absence of direct optical signatures from the cobalt center, the enhanced 3MLCT lifetime and the observed spectral changes strongly indicate intramolecular electron transfer from the Fe(II) center to Co(III), forming a reactive Co(II) species capable of proton reduction. This directional transfer is facilitated by the conductive 4,4′-bipyridine linker, which enables efficient electronic communication while minimizing non-radiative losses. The results confirm that covalent integration of the catalyst into the photosensitizer framework not only stabilizes the key excited state but also enables a more efficient, stepwise charge transfer pathway essential for photocatalytic applications. These findings provide critical insight into the design principles for next-generation base metal dyads in solar fuel generation.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com