Femtosecond Excited-State Dynamics of an Iron(II) Polypyridyl Solar Cell Sensitizer Model

Abstract

Time-resolved electronic absorption spectroscopy on a ∼100 fs time scale has been used to study excited-state dynamics in an FeII polypyridyl complex. [Fe(tren(py)3)]2+, where tren(py)3 is tris(2-pyridylmethyliminoethyl)amine, forms a 1MLCT excited state upon irradiation at 400 nm and is known from previous studies to undergo relaxation to a low-lying ligand-field state having S = 2. Static absorption measurements on the low-spin parent complex and a high-spin analogue have been used to identify spectroscopic signatures for the S = 0 and S = 2 ligand-field states, respectively. Comparison of these data with femtosecond and nanosecond differential absorption spectra establishes that the net ΔS = 2 intersystem crossing is essentially complete in well under 1 ps. Spectroelectochemistry on [Fe(tren(py)3)]2+ has also been used to find an absorption feature characteristic of the initially formed 1MLCT state at λ ≳ 600 nm. Analysis of single-wavelength kinetics data in this spectral region reveals that the charg...