Hydrolysis and substitution effects on the optical properties of coumarin derivatives studied by vibrational spectroscopy and DFT calculation

Article abstract of DOI:10.1016/j.molstruc.2018.05.012

A series of coumarin derivatives have been successfully synthesized. All compounds have been characterized by means of IR and Raman vibrational spectroscopic techniques at the solid state level. Optical absorption and photoluminescence measurements were p

Full text of DOI:10.1016/j.molstruc.2018.05.012

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Hydrolysis and substitution effects on the optical properties of coumarin derivatives
studied by vibrational spectroscopy and DFT calculation
Sirine Khemakhem, Slim Elleuch, Najla Ben Azaza, Houcine Ammar, Younes Abid
PII:
S0022-2860(18)30568-4
10.1016/j.molstruc.2018.05.012
MOLSTR 25184
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 21 December 2017
Revised Date: 3 May 2018
Accepted Date: 4 May 2018
Please cite this article as: S. Khemakhem, S. Elleuch, N. Ben Azaza, H. Ammar, Y. Abid, Hydrolysis and
substitution effects on the optical properties of coumarin derivatives studied by vibrational spectroscopy
and DFT calculation, Journal of Molecular Structure (2018), doi: 10.1016/j.molstruc.2018.05.012.
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Hydrolysis and substitution effects on the optical properties of coumarin
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derivatives studied by vibrational spectroscopy and DFT calculation
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Sirine Khemakhem1,*, Slim Elleuch1, Najla Ben Azaza2, Houcine Ammar2, Younes Abid1
1 Laboratory of Applied Physics, Faculty of Science, University of Sfax, 3038 Sfax, Tunisia
2 Laboratory of Applied Chemistry, Faculty of Science, University of Sfax, 3038 Sfax,
Tunisia
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* Corresponding author: khemakhemsirine@hotmail.fr (Sirine Khemakhem)
Abstract
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A series of coumarin derivatives have been successfully synthesized. All compounds have
been characterized by means of IR and Raman vibrational spectroscopic techniques at the solid
state level. Optical absorption and photoluminescence measurements were performed on thin
solid films. All compounds show absorption bands involving both π-π* and n-π* electronic
transitions and strong emissions in the blue-green spectral range. A large Stokes shift has
been noticed and may explain the light emission stability even at ambient temperature. We
have mainly interested to the hydrolysis and the methoxy substitution at position 8 effects the
optical properties using experimental results and theoretical calculations. Discussions
revealed that the maximum of absorption and emission spectra were affected and shifted by
tuning the gap energy and enhancement of the Stokes shift. One noticed a good agreement
between experimental and theoretical results.
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Keywords: Coumarins, Hydrolysis, Substitution, Vibrational studies, Optical properties,
DFT calculations.
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1. Introduction
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Coumarin and its derivatives have caught considerable attention because of their diverse
photophysical and photochemical properties [1]. They have been widely used in the fields of
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biology, medicine, perfumes and cosmetics [2-4]. Recently, they have caught much attention
thanks to their high fluorescence quantum yield, large Stokes shift, excellent light stability,
and less toxicity. Moreover, coumarin is one of the most efficient fluorescent dyes currently
used. The spectroscopic properties of coumarin have received considerable attention thanks to
their ability to laser in blue-green region. The optical properties of coumarins in the gas phase
have been described by several experimental and theoretical studies. Many studies have been
made and devoted to the effects of solvent, temperature, substitution nature and position on
the photophysical properties on these dyes. [5-19]
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So far, these studies have established some obvious facts such as the transitions nature,
which are mainly a π-π* or n-π* excitations involving a charge displacement within dyes.
Also, the substitution by methoxy group, as donor, on position 5, 6 or 7 has shown great
enhancement of fluorescence intensities and shifts of the absorption and emission
wavelengths. Also, the presence in the 3-position of an electron withdrawing group, proved to
be of a vital importance to the photophysical behavior and allows another push-pull system
with the donor. Polarity of the used solvents has been also been recognized as a key parameter
for modifying fluorescence energy and intensity. Indeed, it’s worthy to note that the majority
of these studies is made on liquid solutions and, in our knowledge, there is rarely found works
done on solid state optical properties of such coumarin and derivatives [5].
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In this context, it was decided in this study to investigate the photophysical properties of
substituted coumarin and their iminocoumarin analogues at the solid state level. Dyes where
the donor methoxy group is borne in the 8-position and a withdrawing nitro-phenyl group in
the 3-position are experimentally and theoretically explored. In fact, we have used
Knoevenagel Protocol for the synthesis and spincoating technique for thin films elaboration.
The synthesized compound has been characterized by IR and Raman spectroscopy and the
optical properties have been investigated by UV-Visible absorption and photoluminescence
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