Figure 1.

Simplified PYP photocycle at room temperature and neutral pH. Intermediates GSI, I₀, and I₀^‡ are populated on the picosecond timescale. The pR intermediate is populated within a few nanoseconds and has a red-shifted (465 nm) absorption maximum compared with the dark state (446 nm). The pR state consists of two conformations: pR_E46Q and pR_CW. Further rotation of the phenolate moiety forms the pB intermediate, with blue-shifted absorption (355 nm). The pB state relaxes back to the dark-state pG on the millisecond timescale.