Abstract
The fluorescence excitation spectra of pyrene complexes with n-alkanes are reported for the S 0 → S 1 and S 0 → S 2 transitions. The S 2 spectral shifts are predictable from theory, and by comparison with other molecules, such as perylene. On the other hand, the S 1 Resonances of pyrene complexes show unusually small displacements from those of the parent species. The spectra of the butane, pentane and hexane complexes actually exhibit net blue shifts. This behaviour provides good evidence for a repulsive interaction in the S 1 state, which is not observed in S 2. Moreover, because the butadiene and benzene complexes give predictable red shifts ⩾ 100 cm −1, and these are found to have plane-parallel geometries, the blue shift correlates with a host carbon—guest hydrogen interaction in the repulsive regime. We also report that the ethylene complex of pyrene exhibits a net blue shift on the S 0 → S 1 transition, and a red shift on S 0 → S 2 only 75% of the predicted value, based on measurements with perylene complexes. This behaviour strongly indicates that ethylene-pyrene has a T-shaped configuration, as predicted by potential energy calculations.
Published Version
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