Solvatochromic behavior of substituted 4-(nitrostyryl)phenolate dyes in pure solvents and in binary solvent mixtures composed of water and alcohols

Article abstract of DOI:10.1016/j.molliq.2018.05.042

Several 4-(nitrostyryl)phenolates have been used recently as solvatochromic dyes in the investigation of pure solvents. Changes in their molecular structures allow a comparison of their solvation patterns to be made in different binary solvent mixtures, in an effort to relate structural factors to the preferential solvation (PS) observed in these media. Firstly, the solvatochromism of four of these probes was studied and a reversal in their solvatochromism was verified, which was expected following a comparison with other similar systems previously studied. The solvatochromic behavior of a series of twelve 4-(nitrostyryl)phenolate dyes was then investigated in water-alcohol mixtures. A sigmoid behavior was verified for one of the dyes in ethane-1,2-diol-water mixtures, and the dye was preferentially solvated by water in the alcohol-rich region. For all other mixture compositions a strong synergy was observed, with the PS of the dye molecules occurring through the less polar moiety of the water-alcohol aggregates in the binary mixtures. In addition, synergy was observed for some dyes, with PS occurring through the less polar moiety of the alcohol-water aggregates. For all of the other water-alcohol mixtures, the probes were preferentially solvated by the alcohol cosolvent. In order to quantify these deviations, a PS (or non-ideality) index PSI was proposed. The PSI values obtained correlated well with the hydrogen-bond donating ability of the alcoholic co-solvent, and also with the basicity of the phenolate dyes, and the trends observed were confirmed with data from the literature for two other phenolate dyes.

Full text of DOI:10.1016/j.molliq.2018.05.042

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Accepted Manuscript
Solvatochromic behavior of substituted 4-(nitrostyryl)phenolate
dyes in pure solvents and in binary solvent mixtures composed of
water and alcohols
Rafaela I. Stock, Crislaine Sandri, Marcos C. Rezende, Vanderlei
G. Machado
PII:
DOI:
Reference:
S0167-7322(18)31088-2
doi:10.1016/j.molliq.2018.05.042
MOLLIQ 9097
To appear in:
Journal of Molecular Liquids
Received date:
Revised date:
Accepted date:
2 March 2018
8 May 2018
9 May 2018
Please cite this article as: Rafaela I. Stock, Crislaine Sandri, Marcos C. Rezende, Vanderlei
G. Machado , Solvatochromic behavior of substituted 4-(nitrostyryl)phenolate dyes in pure
solvents and in binary solvent mixtures composed of water and alcohols. The address
for the corresponding author was captured as affiliation for all authors. Please check if
appropriate. Molliq(2017), doi:10.1016/j.molliq.2018.05.042
This is a PDF file of an unedited manuscript that has been accepted for publication. As
a service to our customers we are providing this early version of the manuscript. The
manuscript will undergo copyediting, typesetting, and review of the resulting proof before
it is published in its final form. Please note that during the production process errors may
be discovered which could affect the content, and all legal disclaimers that apply to the
journal pertain.

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
ACCEPTED MANUSCRIPT
1
Solvatochromic behavior of substituted 4-(nitrostyryl)phenolate
dyes in pure solvents and in binary solvent mixtures composed
of water and alcohols
Rafaela I. Stock a, Crislaine Sandri a, Marcos C. Rezende b,*, Vanderlei G. Machado a,*
a Department of Chemistry, Universidade Federal de Santa Catarina,
Florianópolis, SC, Brasil
bFacultad de Química y Biología, Universidad de Santiago de Chile, Santiago,
Chile
*Corresponding authors.
E–mail addresses: vanderlei.machado@ufsc.br (V. G. Machado); marcos.caroli@usach.cl
(M. C. Rezende).

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
ACCEPTED MANUSCRIPT
2
Abstract
Several 4-(nitrostyryl)phenolates have been used recently as solvatochromic dyes in
the investigation of pure solvents. Changes in their molecular structures allow a comparison
of their solvation patterns to be made in different binary solvent mixtures, in an effort to
relate structural factors to the preferential solvation (PS) observed in these media. Firstly, the
solvatochromism of four of these probes was studied and a reversal in their solvatochromism
was verified, which was expected following a comparison with other similar systems
previously studied. The solvatochromic behavior of a series of twelve 4-
(nitrostyryl)phenolate dyes was then investigated in water-alcohol mixtures. A sigmoid
behavior was verified for one of the dyes in ethane-1,2-diol-water mixtures, and the dye was
preferentially solvated by water in the alcohol-rich region. For all other mixture compositions
a strong synergy was observed, with the PS of the dye molecules occurring through the less
polar moiety of the water-alcohol aggregates in the binary mixtures. In addition, synergy was
observed for some dyes, with PS occurring through the less polar moiety of the alcohol-water
aggregates. For all of the other water-alcohol mixtures, the probes were preferentially
solvated by the alcohol cosolvent. In order to quantify these deviations, a PS (or non-ideality)
index PSI was proposed. The PSI values obtained correlated well with the hydrogen-bond
donating ability of the alcoholic co-solvent, and also with the basicity of the phenolate dyes,
and the trends observed were confirmed with data from the literature for two other phenolate
dyes.
Keywords: solvatochromism; synergism; preferential solvation; solvatochromic reversal;
solute-solvent interactions; binary solvent mixtures.

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
ACCEPTED MANUSCRIPT
3
1. Introduction
The influence of solvents on the rate and the course of many chemical processes is
well known [1, 2], being usually attributed to changes in the medium polarity.
Solvatochromic probes are commonly used in the physicochemical investigation of solvent
properties [1-6]. Reichardt’s pyridinium-N-phenolate betaine dye (1) [6-8] and Brooker’s
merocyanine (2) [9-11] are two solvatochromic dyes which have been used in recent decades
(Scheme 1).
((Scheme 1 here))
In the investigations carried out with respect to solvent effects, a growing interest can
be verified in the study of binary solvent mixtures [12-18]. A very large number of papers
dealing with solute-solvent interactions in binary solvent mixtures have employed
solvatochromic probes to make evident the phenomenon of preferential solvation (PS) in
such media [3-5, 11, 19]. The assumption that the spectral response reflects the composition
of the probe-solvating layer leads to the conclusion that the composition of this cybotactic
region often departs considerably from that of the bulk mixture. This is readily visualized in
plots of the variation of the transition energy (ET) values of the solvatochromic probe with
the binary mixture composition, often expressed as the mole percentage of one of the solvents
[11, 20, 21]. These plots are unique for a particular probe in a certain binary solvent mixture,
since they reflect specific interactions in this three-component system. Nevertheless, if a
series of analogous probes is compared, analogous plots should be obtained, that may shed
light on these specific interactions in solution.