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Electronic and Vibronic Contributions to Two-Photon Absorption in Donor–Acceptor–Donor Squaraine Chromophores

Authors

  • Shino Ohira,

    1. School of Chemistry and Biochemistry and Center of Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332–0400 (USA), Fax: (+1) 404-894-7452
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  • Indranil Rudra Dr.,

    1. School of Chemistry and Biochemistry and Center of Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332–0400 (USA), Fax: (+1) 404-894-7452
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  • Karin Schmidt Dr.,

    1. School of Chemistry and Biochemistry and Center of Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332–0400 (USA), Fax: (+1) 404-894-7452
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  • Stephen Barlow Dr.,

    1. School of Chemistry and Biochemistry and Center of Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332–0400 (USA), Fax: (+1) 404-894-7452
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  • Sung-Jae Chung Dr.,

    1. School of Chemistry and Biochemistry and Center of Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332–0400 (USA), Fax: (+1) 404-894-7452
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  • Qing Zhang Dr.,

    1. School of Chemistry and Biochemistry and Center of Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332–0400 (USA), Fax: (+1) 404-894-7452
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  • Jon Matichak,

    1. School of Chemistry and Biochemistry and Center of Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332–0400 (USA), Fax: (+1) 404-894-7452
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  • Seth R. Marder Prof.,

    1. School of Chemistry and Biochemistry and Center of Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332–0400 (USA), Fax: (+1) 404-894-7452
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  • Jean-Luc Brédas Prof.

    1. School of Chemistry and Biochemistry and Center of Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332–0400 (USA), Fax: (+1) 404-894-7452
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Abstract

Many squaraines have been observed to exhibit two-photon absorption at transition energies close to those of the lowest energy one-photon electronic transitions. Here, the electronic and vibronic contributions to these low-energy two-photon absorptions are elucidated by performing correlated quantum-chemical calculations on model chromophores that differ in their terminal donor groups (diarylaminothienyl, indolenylidenemethyl, dimethylaminopolyenyl, or 4-(dimethylamino)phenylpolyenyl). For squaraines with diarylaminothienyl and dimethylaminopolyenyl donors and for the longer examples of 4-(dimethylamino)phenylpolyenyl donors, the calculated energies of the lowest two-photon active states approach those of the lowest energy one-photon active (1Bu) states. This is consistent with the existence of purely electronic channels for low-energy two-photon absorption (TPA) in these types of chromophores. On the other hand, for all squaraines containing indolinylidenemethyl donors, the calculations indicate that there are no low-lying electronic states of appropriate symmetry for TPA. Actually, we find that the lowest energy TPA transitions can be explained through coupling of the one-photon absorption (OPA) active 1Bu state with bu vibrational modes. Through implementation of Herzberg–Teller theory, we are able to identify the vibrational modes responsible for the low-energy TPA peak and to reproduce, at least qualitatively, the experimental TPA spectra of several squaraines of this type.

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