Cryogenic action spectroscopy of the cyan fluorescent protein chromophore anion

Action spectroscopy at T ≈ 30 K, as a proxy for the visible absorption band, and the branching between electron detachment and dissociation in the cyan fluorescent protein chromophore anion are reported. The cryogenic action spectra, which show the presence of several rotamers, serve as a reference point for interpreting the effect of nano-environmental interactions in complex protein environments. The adiabatic detachment energy for the lowest energy geometric isomer (Z1) is 19 531 ± 40 cm^-1, with the vertical S₁ ← S₀ transition energy at 23 734 ± 40 cm^-1. For Z1, the propensity for internal conversion followed by dissociation is low (<10%) compared with autodetachment as the S₁ ← S₀ absorption band is entirely situated in the detachment continuum and is classified as a shape resonance.