Wide-band TA maps an Fe(II) four-state cascade
Femtosecond TA from 370–1200 nm resolves 1PALCT → 3PALCT → 3MC → 5MC decay in an iron amido chromophore, including a ~100 fs NIR CT signature.
Source
Resolving consecutive excited-state evolution in Fe-amido chromophores by wide-band optical transient absorption spectroscopy
Study at a glance
- Design
- Other — Wide-band ultrafast spectroscopy of Fe amido chromophores resolving PALCT→MC cascade
- N
- Photophysics of molecular Fe complexes — no sample N
- Population
- Iron amido chromophores in toluene
- Outcome
- Consecutive excited-state lifetimes from PALCT through high-spin MC states
Structured fields used in claim comparison tables when every cited study has a complete layer.
What they did
They pumped (CF3L1)2Fe in toluene at 600 nm and probed 370–1200 nm with ~100 fs IRF, using polarization control and 100 µm cells. High-spin (CF3L2)2Fe and spectroelectrochemistry modeled 5MC and PALCT spectra. Global fits extracted oscillations and sequential lifetimes.
What they found
NIR ESA (800–1200 nm) marks PALCT and decays in ~100 fs into a nanosecond 5MC (~3.5 ns). Faster ~50 fs ISC (1PALCT → 3PALCT) precedes that. An isosbestic point at 545 nm (175–325 fs) is assigned to 3MC → 5MC (~250 fs). Coherent Raman modes at 60, 80, and 110 cm–1 appear. High-spin analogue absorbs at 470 nm (ε = 23 600 M–1 cm–1).
The limits
What it doesn't show
The ~50 fs ISC is near the IRF, so the number is an estimate. The four-state model assumes no ground-state recovery before 5MC. Only toluene solutions of two related complexes are measured, not devices or other metals.
Key terms
- PALCT
- π-antibonding-to-ligand charge transfer unique to these amido-Fe chromophores, analogous to MLCT.
- Metal-centered (MC) state
- d–d excited state (3MC or 5MC) that usually quenches Fe(II) CT states in picoseconds or less.
- Optical transient absorption (oTA)
- Pump–probe UV/vis/NIR spectroscopy of excited-state populations versus delay.
- Intersystem crossing (ISC)
- Change of spin multiplicity, here 1PALCT → 3PALCT in ~50 fs.
- Isosbestic point
- Wavelength where two species have equal ΔA, here 545 nm during 3MC → 5MC.
Flashcards
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Quiz yourself
The distinctive PALCT excited-state absorption is mainly in the
Common questions
Why did earlier visible-only TA miss the CT state?
PALCT’s distinctive ESA is in the NIR (800–1200 nm); 400–800 nm looks a lot like 5MC.
What is the long-lived state?
A 5MC lasting ~3.5 ns, matching X-ray emission assignments.
What does (CF3L2)2Fe provide?
A synthetic high-spin ground-state model of the 5MC spectrum.
Sequence of states?
1PALCT → 3PALCT (~50 fs) → 3MC (~100 fs) → 5MC (~250 fs) → ground state (ns).
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