Figure 6.

Proposed models for the observed excitation-driven dynamics: I_ex dependence of the flicker rate at high pH suggests that transitions between bright (B) and dark (D) states occur with low probability via the excited B₁ and D₁ states by routes that are not yet distinguishable. However, the different time scales of excited state lifetimes k_f⁻¹ (ns) and flicker times (microseconds) simplify the kinetic model to a direct interconversion between the two states B ⇌ D. The overall transition rates k_B and k_D are thus linearly dependent on I_ex. At low pH, additional independent reversible proton-binding transitions occur from the B–D system to an externally protonated dark state D_H0.