Photochemical hole burning: A means to observe high resolution optical structures in phycoerythrin

We have investigated the lowest electronic transitions of phycoerythrobilin using laser-induced low temperature photochemistry. Narrow band irradiation into the absorption bands of the native chromophore leads to photochemical holes of the width of about 1–2 cm−1. We attribute the hole burning mechanism to reversible proton rearrangement processes. The high resolution of the experiments allows the resolution of well-defined substructures in the broad absorption bands which we interpret as being due to discrete vibrational states or due to a nonresonant energy transfer mechanism within the highly ordered chromophore–protein configuration.