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Abstract

Single crystals of the aluminophosphate AlP0₄-5 loaded with different amounts of p-nitroaniline (PNA) were investigated by polarized IR microspectroscopy. For a loading of 4 wt % the bands due to PNA were almost totally polarized. From the dicroic ratios a mean deviation of the long molecule axis from the crystal c-axis of around 12° can be inferred. At higher loading levels H bonding between adjacent PNA molecules reduces the symmetry, thus leading to dicroic ratios closer to unity. However, absorption bands related to the aromatic ring are less affected by the H bonding and show dicroic ratios comparable to those of the lowly loaded samples. This means that also in the high-loading situation the orientation of the molecules by the channel system is very high. Heating of the highly loaded sample to up to 573 K leads to a breaking of the H bonds, the spectrum changes from a solid like type to a solution type spectrum