Abstract
The fluorescence excitation spectra are reported for van der Waals complexes of perylene with tetramethylsilane (TMS), 1,3-butadiene, ethylene and CO 2. The 1:1 complexes with TMS, ethylene and butadiene have simple spectra, and the spectral red shifts are predictable from solvent-shift theory, while the CO 2 complexes are shown to exhibit anomalously small red shifts and extended low-frequency mode progressions. Dispersed fluorescence of the assigned 1:1 CO 2 complexes is consistent with the excitation spectrum, indicating a substantial difference in the equilibrium conformation of the complex between the two electronic states of the host molecule. Potential energy calculations using a point coulombic charge correction predict a non-center-of-mass geometry for CO 2 complexes, consistently with the observed spectra. Calculations of the binding energies are shown to be in satisfactory agreement with experimental data (1250, 1295–1398 and 2300–2580 cm −1 for CO 2, C 2H 4 and C 4H 6, respectively). At the 2:1 complexation level, while butadiene and TMS appear to form the expected trans conformers, the ethylene and CO 2 complexation spectra indicate the presence of guest molecule aggregates. In these cases, guest-guest interactions are evidently competing with the usually dominant process of molecular adsorption onto the host species.
Published Version
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