Theoretical study of the electronic excited states and fluorescence spectra of squaraine in solution

Hitoshi Ozawa, Kazunori Yashiro, Takuma Yamamoto, Satoshi Yabushita

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)


Bis[4-(dimethylamino)phenyl]squaraine (SQ-DMA) has been used as a long wavelength fluorescence dye. In spite of various experimental and theoretical studies, its excited state properties and the relaxation mechanism have not been elucidated. In this work, we tried to clarify these points from a theoretical point of view. The heats of reaction from the planar to possible twisted conformers in the first excited state S1 in solvents were calculated to be significantly endothermic, thus the twisted structures turn out to be less important, which contradicts earlier proposals made in experimental studies. This behavior is in a sharp contrast with that of the related molecule 4-(N,N-dimethylamino)benzonitrile, and is explained by the difference in their electronic characters of their relevant excited states; the S1 state of SQ-DMA is a simple HOMO-to-LUMO excited state with a delocalized character. Furthermore, the theoretically simulated absorption and fluorescence spectra with the planar structure of SQ-DMA are in good agreement with the corresponding experimental results. These results suggest that the responsible S1 state is the lowest 1B1u state with a planar D2h structure.

Original languageEnglish
Pages (from-to)1625-1643
Number of pages19
JournalJournal of Solution Chemistry
Issue number9-10
Publication statusPublished - 2014 Oct 21


  • Fluorescence spectrum
  • SQ-DMA
  • Squaraine
  • TICT

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology
  • Physical and Theoretical Chemistry


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