Pressure induced reorientation and aggregation of pheophytin in monomolecular layers

Monomolecular layers of pheophytin were investigated by absorption spectroscopy, by thermodynamic, and by light‐ and electron microscopical measurements. — It is shown, that a pressure increase induces reorientations of the porphyrin rings. At pressures above a critical value pk pheophytin aggregates in an arrangement with coplanar stacking of the porphyrin rings. Size and shape of the aggregates are determined microscopically. The diameters amount to 2 μm, the thickness to 500 Å. — The results prove the stability of the monolayers for pressures below pk = 15 dyn/cm and the existence of instable phases at higher pressures.