I have been learning a little more about phytochromes which are a important class of photo-active biomolecules. This was stimulated by my previous post about single molecule spectroscopy studies of a photosynthetic protein containing phytochromes.
I mention here two recent PNAS papers that I found particularly interesting. I just include some key text and figures from the papers.
Ultrafast excited-state isomerization in phytochrome revealed by femtosecond stimulated Raman spectroscopy
Photochemical interconversion between the red-absorbing (Pr) and the far-red-absorbing (Pfr) forms of the photosensory protein phytochrome initiates signal transduction in bacteria and higher plants. The Pr-to-Pfrtransition commences with a rapid Z-to-E photoisomerization at the C15C16 methine bridge of the bilin.
This paper reports evidence that this isomerization occurs on the excited state potential energy surface.
Phytobilin chromophores can underdo two further possible rotations of the end rings following absorption of red light. Different proteins favour different rotations of these D rings.
The associated quantum chemistry has been considered in Deciphering Intrinsic Deactivation/Isomerization Routes in a Phytochrome Chromophore Model