Shape of the Q band in the absorption spectra of porphyrin nanotubes: Vibronic coupling or exciton effects?

Absorption and linear dichroism spectra of self-assembled tubular aggregates of TPPS 4 porphyrin are studied theoretically with special emphasis on the low energy part of the spectra (the Q band region) where the coupling with intramolecular vibrations is pronounced. The model Hamiltonian includes b...

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Bibliographic Details
Published in:The Journal of chemical physics 2010-09, Vol.133 (9), p.094701-094701-10
Main Authors: Stradomska, Anna, Knoester, Jasper
Format: Article
Language:English
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Summary:Absorption and linear dichroism spectra of self-assembled tubular aggregates of TPPS 4 porphyrin are studied theoretically with special emphasis on the low energy part of the spectra (the Q band region) where the coupling with intramolecular vibrations is pronounced. The model Hamiltonian includes both the excitonic coupling between four molecular electronic excited states contributing to the porphyrin Q and B bands as well as the intermediate-strength linear exciton-phonon coupling to one effective high-frequency molecular vibrational mode. Good agreement between the calculated and experimental spectra is obtained. The results allow us to identify the nature of the peaks observed in the Q band region of the aggregate's absorption spectrum; we show that the two most prominent peaks within the Q band originate from two different excitonic subbands. It is shown that the coupling between the Q and B bands plays an important role and the vibronic coupling affects the details of the absorption lineshape.
ISSN:0021-9606
1089-7690
DOI:10.1063/1.3481654