Suppression of Kasha’s rule in higher excited states of 4-pyrilocyanines

Yuri P. Piryatinski, Anatoli B. Verbitsky, Petro Lutsyk, Oleksiy Rozhin, Oleksiy Kachkovsky, Yaroslav Prostota, Volodymyr Brovarets, Volodymyr Kurdyukov

Research output: Contribution to journalConference article

Abstract

Spectral properties of the series of cationic polymethine dyes containing conjugated chain of different length and 4-pyrylium terminal groups were studied in details. Besides, the steady-state long-wavelength fluorescence from the lowest excited state and the fluorescence from higher excited states were experimentally revealed. The steady-state fluorescence band from the lowest excited state is shifted bathochromically with lengthening of the polymethine chain, which is also reflected in the absorption shift. According to quantum-chemical modeling, the appearance of unconventional fluorescence, which suppresses Kasha’s rule, is associated with the different nature of the lowest excited states: the first and forth transitions are typical polymethine electron transitions involved only totally delocalized molecular orbitals (MOs), whereas the second and third transitions correspond to the electron jumping from the degenerated MOs localized only within the terminal groups (so called quasi-local MOs and hence quasi-local transitions). The forbidden transitions between the excited states of different types stimulate the fluorescence from the higher excited states.

Original languageEnglish
Pages (from-to)33-40
Number of pages8
JournalMolecular Crystals and Liquid Crystals
Volume672
Issue number1
DOIs
Publication statusPublished - 13 Jun 2019
Event1th International Conference on Electronic Processes in Organic and Inorganic Materials (ICEPOM-11) - Ivano-Frankivsk, Ukraine
Duration: 21 May 201825 May 2018

Keywords

  • higher excited states
  • Kasha's rule
  • quantum-chemical modeling
  • unconventional fluorescence

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