PHOTOISOMERIZATION OF MOLECULAR VAN-DER-WAALS AGGREGATES - STRUCTURAL ASSIGNMENTS OF ISOMERIC FORMS OF 1-CHLOROBUTANE PERYLENE VIA ROTATIONAL COHERENCE SPECTROSCOPY

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 almost-equal-to 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.