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

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.

Publication DOI: https://doi.org/10.1080/15421406.2018.1542104
Divisions: Engineering & Applied Sciences > Electrical, Electronic & Power Engineering
Engineering & Applied Sciences > Aston Institute of Photonics Technology
Engineering & Applied Sciences
Uncontrolled Keywords: higher excited states,Kasha's rule,quantum-chemical modeling,unconventional fluorescence,Chemistry(all),Materials Science(all),Condensed Matter Physics
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Related URLs: http://www.scop ... tnerID=8YFLogxK (Scopus URL)
https://www.tan ... 06.2018.1542104 (Publisher URL)
Published Date: 2019-06-13
Authors: Piryatinski, Yuri P.
Verbitsky, Anatoli B.
Lutsyk, Petro ( 0000-0002-7004-1946)
Rozhin, Oleksiy ( 0000-0003-2271-8227)
Kachkovsky, Oleksiy
Prostota, Yaroslav
Brovarets, Volodymyr
Kurdyukov, Volodymyr

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Version: Accepted Version

Access Restriction: Restricted to Repository staff only until 13 June 2020.


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