The nature of singlet excitons in oligoacene molecular crystals

Journal Article · Sat Jan 01 04:00:00 EST 2011 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.3590871· OSTI ID:1066070

Yamagata, H. ^[1]; Norton, J. ^[2]; Hontz, E. ^[1]; Olivier, Y. ^[3]; Beljonne, D. ^[3]; Bredas, J. L. ^[2]; Silbey, R. J. ^[4]; Spano, F. C. ^[1]

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1. Temple Univ., Philadelphia, PA (United States)
2. Georgia Inst. of Technology, Atlanta, GA (United States). Center for Organic Photonics and Electronics
3. Univ. of Mons (Belgium). Lab. for Chemistry of Novel Materials
4. MIT (Massachusetts Inst. of Technology), Cambridge, MA (United States). Dept of Chemistry and Center for Excitonics

A theory for polarized absorption in crystalline oligoacenes is presented, which includes Frenkel exciton coupling, the coupling between Frenkel and charge-transfer (CT) excitons, and the coupling of all neutral and ionic excited states to the dominant ring-breathing vibrational mode. For tetracene, spectra calculated using all Frenkel couplings among the five lowest energy molecular singlet states predict a Davydov splitting (DS) of the lowest energy (0–0) vibronic band of only -32 cm^-1, far smaller than the measured value of 631 cm^-1 and of the wrong sign--a negative sign indicating that the polarizations of the lower and upper Davydov components are reversed from experiment. Inclusion of Frenkel-CT coupling dramatically improves the agreement with experiment, yielding a 0–0 DS of 601 cm^-1 and a nearly quantitative reproduction of the relative spectral intensities of the 0–n vibronic components. Our analysis also shows that CT mixing increases with the size of the oligoacenes. We discuss the implications of these results on exciton dissociation and transport.

• Research Organization: Energy Frontier Research Centers (EFRC) (United States). Center for Excitonics (CE)
• Sponsoring Organization: USDOE SC Office of Basic Energy Sciences (SC-22); National Science Foundation
• DOE Contract Number: SC0001088
• OSTI ID: 1066070
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 20 Vol. 134; ISSN JCPSA6; ISSN 0021-9606
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

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