Density functional predicted geometries and vibrational frequencies of the neutral and anion-radical form of pheophytin: relevance to electron transfer in photosynthetic reaction centres

Hybrid density functional calculations, B3LYP, are used to predict the geometry and harmonic vibrational frequency changes which occur on one electron reduction of pheophytin to its anion-free radical. Calculated shifts in frequency for the 131CO and 133CO stretching frequencies are shown to be in excellent agreement with experimental determinations. Frequency changes on reduction are shown to be correlated with small bond length changes which in turn are a reflection of the electron density distribution of the singly occupied molecular orbital of the anion-free radical formed.