Left, Sorghum bicolor; Right Glycine max. Above: RR spectra of the Pr states (blue traces) and their photoconversion products (red traces) obtained upon 670 and 750 nm irradiation at ambient temperature. All spectra were measured at 90 K with 1064 nm excitation. The spectral regions labelled are indicative of (i) the methine bridge configurations and conformations (C=C stretching modes of the A-B and C-D methine bridges at ca. 1600–1650 cm−1), (ii) pyrrole nitrogen protonation state (N-H in-plane bending modes of rings B and C at ca. 1550 – 1580 cm−1) and (iii) the C-D methine bridge torsion (hydrogen-out-of-plane [HOOP] mode at ca. 795 - 825 cm−1). The broad feature at ca. 1460 cm−1 is largely due to non-resonant Raman bands of the protein. The high intensity of this feature relative to the RR bands of the chromophore indicates that the latter experience a low resonance enhancement. Below: IR “photoproduct minus Pr” difference spectra obtained upon irradiation with 670 and 750 nm at ambient temperature. The positive signals indicated by black lines and labels refer to the photoproduct, whereas the grey lines and labels mark the signals of the Pr state. Representative spectra based on at least two samples are shown. Spectra for each sample were measured several times. Each spectrum is based on 1000 separate FT scans.