Electronic and vibronic contributions to two-photon absorption in donor-acceptor-donor squaraine chromophores

Shino Ohira, Indranil Rudra, Karin Schmidt, Stephen Barlow, Sung Jae Chung, Qing Zhang, Jon Matichak, Seth R. Marder, Jean Luc Brédas*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

45 Scopus citations


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 indolinylidenemethyldonors, 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.

Original languageEnglish (US)
Pages (from-to)11082-11091
Number of pages10
JournalChemistry - A European Journal
Issue number35
StatePublished - Dec 8 2008
Externally publishedYes


  • Chromophores
  • Nonlinear optics
  • Squaraines
  • Two-photon absorption
  • Vibronic coupling

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry


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