Spectroscopy, dynamics and structures of jet formed anthracene clusters Original Research Article

The spectroscopy and dynamics of the lowest excited states of the jet formed anthracene clusters (n<6) were investigated by fluorescence, fluorescence depletion and mass selected excitation spectroscopy. For all cluster sizes, only excimer emission was detected, indicating that the relaxation proceeds predominantly by an electron transfer between the initially excited state and an ionic state. For the anthracene trimer, the existence of two isomers characterised by different relaxation types has been evidenced. The dynamics of the anthracene clusters indicate also the existence of other non-radiative relaxation processes. Both calculations and experimental results show that excitonic interaction is the source of only limited effects in the species excited state spectroscopy. The structures of tetramer and pentamer obtained from model potential calculations show similarities with the arrangement of the molecules in the crystal. A structure similar to that determined for the naphthalene trimer is inferred for the isomer of the anthracene trimer on the basis of (i) close analogies between the species spectroscopy and (ii) similar structure corresponding to the deepest minima of the trimer ground-state potential energy surface obtained by ab initio calculations.