Two kinds of excimers in α-perylene and pyrene crystals: Origin of Y and V emissions
1989; Elsevier BV; Volume: 130; Issue: 1-3 Linguagem: Inglês
10.1016/0301-0104(89)87072-7
ISSN1873-4421
Autores Tópico(s)Luminescence and Fluorescent Materials
ResumoTwo kinds of excimers can exist in molecular crystals composed of card-packed dimeric units; a stable one on one of these units and a metastable one on two next-nearest parallel molecules. There exists an adiabatic potential barrier between them reflecting that lattice distortions stabilizing either one destabilize the other. Both the Y emission from α-perylene and the V emission from supercooled pyrene, observed below 70 K, are attributed to the metastable excimer, while the more Stokes-shifted and broad E emission observed above 30 K, is attributed to the stable excimer. Both excimers are optically forbidden, emitting light with the aid of intramolecular phonons at either of the two molecules composing them. These features enable one to reproduce successfully characteristic phonon strucures in the Y and V emissions whose origin has been a subject of long-standing controversies. In the E emission, individual lines broaden so much that they merge into a single broad band.
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