Photochemically generated •Y356. Time-resolved spectroscopic data are recorded after excitation (λex = 355 nm) of met-[Re]-S355C-β2. Top: Transient absorption spectrum of [Re]-S355C-β2 collected 1 μs after excitation (65 μM in 50 mM HEPES, 32.5 mM RuIII(NH3)6Cl3, 1 mM EDTA, pH 8.0). The spectrum shown is obtained from 2,500 four-spectrum sequences taken on two samples (1,250 four-spectrum sequences each), averaged, and smoothed using a low-pass filter on the basis of a fast Fourier transform (FFT). Bottom: Transient absorption kinetics for transient •Y356 (λobs = 408 nm) and a biexponential fit (blue) (50 μM in 69% 50 mM HEPES, 25 mM RuIII(NH3)6Cl3, 1 mM EDTA, pH 8.0) (τ1 = 8.1 ± 1.1 μs, τ2 = 2.0 ± 0.8 μs 31%). The trace shown is obtained from 5,000 sweeps (averages) taken on a single sample.