Premium
Optical Absorption and Photo‐Luminescence Spectra of Molecular van der Waals Systems: Frenkel Exciton Resonance Effects
Author(s) -
Fleming Alexander J.,
Coleman Jonathan N.,
Blau Werner J.
Publication year - 2005
Publication title -
macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 1022-1360
DOI - 10.1002/masy.200551150
Subject(s) - exciton , resonance (particle physics) , biexciton , intermolecular force , van der waals force , atomic physics , absorption (acoustics) , molecular physics , luminescence , physics , absorption spectroscopy , molecule , chemistry , condensed matter physics , quantum mechanics , optics
Applying the principle of conservation of energy, the photo‐absorption‐luminescence (p‐a‐l) cycle of resonant Frenkel excitons in aggregates is explained in terms of the p‐a‐l cycles of isolated molecules. The method employed to measure the Stokes shift of Frenkel Exciton Resonance (FER) systems, derived from our model, is found to differ significantly from that employed currently. Our postulate, that the aggregate v‐e transition energy, in the frame of reference of a resonant exciton, decreases as function of the localisation length of the exciton, is demonstrated by the excellent agreement of the model with existing data. This has allowed the determination of the localisation length of resonant excitons from readily available spectra. As the localisation length is a good indicator of the order of a system, this result will be useful in molecular self‐assembly (MSA) research. Results from the model suggest that Frenkel exciton resonance is vibrationally modulated, and the collective exciton eigenstate of a resonant Frenkel exciton can couple the v‐e manifolds of 2 N molecules together via the electronic resonance interaction, even in the absence of direct intermolecular vibrational coupling. In essence, we demonstrate that the photo‐physics of an exciton that is resonant over many molecules is fundamentally determined by the photo‐physics of the isolated molecule just as one would expect.