Optical selection rule for the lower Davydov excitons in co-oligomer single crystals

Kazuki Bando, Toshiteru Nakamura, Seiji Fujiwara, Yasuaki Masumoto, Fumio Sasaki, Shunsuke Kobayashi, Yukihiro Shimoi, and Shu Hotta
Phys. Rev. B 77, 045205 – Published 15 January 2008

Abstract

Intrinsic optical transitions of lower Davydov excitons in thiophene/phenylene co-oligomer (TPCO) crystals were investigated. Lower Davydov excitons are either optically allowed or forbidden depending on the number of thiophene rings constituting the TPCOs. The TPCO molecules are orientated nearly parallel to each other like H aggregates and are aligned in herringbone fashion within a crystalline layer. The transition selection rules are dominated by the components of the molecular transition dipole moments lying in the herringbone planes of the respective crystals. The selection rules at the exciton band bottoms of the TPCOs differ from those of oligothiophenes in spite of these two compounds having similar molecular structures. The selection rules vary drastically with the molecular alignment because of the H aggregation. TPCO and oligothiophene crystals are treated as H aggregates as a first approximation. This treatment is very useful for understanding the optical transitions of conjugated materials.

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  • Received 4 October 2007

DOI:https://doi.org/10.1103/PhysRevB.77.045205

©2008 American Physical Society

Authors & Affiliations

Kazuki Bando*, Toshiteru Nakamura, Seiji Fujiwara, and Yasuaki Masumoto

  • Institute of Physics and Center for Tsukuba Advanced Research Alliance (TARA), University of Tsukuba, Tsukuba 305-8571, Japan

Fumio Sasaki and Shunsuke Kobayashi

  • Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8568, Japan

Yukihiro Shimoi

  • Nanotechnology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8568, Japan

Shu Hotta

  • Department of Macromolecular Science and Engineering, Graduate School of Science and Technology, Kyoto Institute of Technology, Kyoto 606-8585, Japan

  • *bando@sakura.cc.tsukuba.ac.jp

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Issue

Vol. 77, Iss. 4 — 15 January 2008

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