Rotational coherence measurements and structure calculations of hydrogen-bonded complexes of perylene with water and alcohols

Rotational coherence spectroscopy has been used to measure the inertial properties of 1:1 complexes of perylene with water and several different aliphatic alcohols, under supersonic expansion conditions. Hole-burning experiments confirm that several complexes, including ethanol, I-propanol, and 2-propanol, are present in at least two distinct structural forms. On the other hand, for the methanol and tert-butyl alcohol complexes, only a single structure was detected. The water complex also exists in two ground-state forms, but so far only one of these has been structurally identified. Structures calculated via molecular mechanics procedures, using the CVFF and CFF91 force fields and parameters from the Biosym protein database, are remarkably consistent with experimental inertial measurements. Some comparisons with other molecular mechanics procedures are also presented. We have determined that ail these complexes involve a hydrogen bond to pi-electrons in the outer rings of the aromatic molecule. The structural variants usually involve rotation about this bond site to different registry positions with the perylene aromatic rings, effectively conserving the alcohol geometry. However, one form of the l-propanol complex may involve a gauche isomer of the alcohol molecule.