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.