Photoisomerization of molecular van der Waals aggregates. Structural assignments of isomeric forms of 1-chlorobutane/perylene via rotational coherence spectroscopy

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Van der Waals complexes of perylene with 1-chlorobutane, prepared under supersonic jet conditions, exist in three distinct isomeric forms distinguishable by their spectral red-shifts of 265,238 and 184 cm −1. Following vibronic excitation at 355 cm −1, two of these isomers yield similarly shaped and broadened fluorescence bands of ≈ 180 cm −1 width, suggesting a rapid isomerization. A third isomer is not coupled, showing a distinct spectrum even for a vibrational energy of 700 cm −1. Structure determinations of all three isomers are reported using rotational coherence spectroscopy. The existence is demonstrated of three remarkably different binding sites for 1-chlorobutane on the perylene surface.