Near-IR Absorption Spectrum of Aromatic Excimers

The absorption spectrum of excimers in fluid media has been measured with 1-methylnaphthalene, anthracene, pyrene, and perylene. In all compounds studied an absorption band characteristic of an excimer has been observed in the near-IR. It is shown that the IR band can be understood by assuming that an excimer is essentially a charge-transfer complex:  The near-IR band is to be assigned to a transition from the lowest excimer state to a higher state which has an ion-pair character.