The photoisomerization mechanism of the chromophore of bacterial biliverdin (BV) phytochromes is explored with the nonadiabatic dynamics simulation by using the on-the-fly trajectory surface-hopping method at the semi-empirical OM2/MRCI level. Particularly, the current study focuses on the influence of the geometrical constrains on the nonadiabatic photoisomerization dynamics of the BV chromophore. Here a rather simplified approach is employed in the nonadiabatic dynamics to capture the features of geometrical constrains, which adds the mechanical restriction on the specific moieties of the BV chromophore. This simplified method provides a rather quick approach to examine the influence of the geometrical restrictions on the photoisomerization. As expected, different constrains bring the distinctive influences on the photoisomerization mechanism of the BV chromophore, giving either strong or minor modification of both involved reaction channels and excited-state lifetimes after the constrains are added in different ring moieties. These observations not only contribute to the primary understanding of the role of the spatial restriction caused by biological environments in photoinduced dynamics of the BV chromophore, but also provide useful ideas for the artificial regulation of the photoisomerization reaction channels of phytochrome proteins.
The Impact of the Different Geometrical Restrictions on the Nonadiabatic Photoisomerization of Biliverdin Chromophore