**Author details**

*Δ*Ð

ð Þ¼ **<sup>1</sup>** <sup>0</sup>*:*<sup>19</sup> **<sup>&</sup>gt;** *<sup>Δ</sup>*<sup>Ð</sup>

**4. Conclusions**

region at all measured mole fractions.

ð Þ¼ **2a** <sup>0</sup>*:*<sup>071</sup> **<sup>&</sup>gt;** *<sup>Δ</sup>* <sup>Ð</sup>

*Dyes and Pigments - Novel Applications and Waste Treatment*

as water solutions and mixtures with polar organic solvents.

The authors declare no competing financial interest.

The author would like to thank Dr. D. Matiadis (NCSR Demokritos, Athens, Greece) for fruitful discussions revolving around the solvatochromism of heterocyclic compounds. IKY (Greek State Scholarship Foundation) is gratefully acknowledged for financial support to R.P. during his PhD; a part of this work is connected

**Acknowledgements**

to the work carried out then.

**Notes**

**28**

drawn when comparing the isosolvation points for the different probes of all compounds (**Table 5**). The results clearly illustrate a different probing aptitude of preferential solvation by the azo group of compound **1**. Of course all results indicate qualitatively the same PS effect i.e. EG is the preferred solvent in the cybotactic

A general conclusion of the present study is that two distinct functional groups acting as chromophores (specifically the FC and azo groups) can probe solvation effects in different ways however this is true only on a quantitative basis. Qualitatively, both functional groups probed a strong negative solvatochromic effect in all cases of molecules studied. It became apparent though that FC is more sensitive to the dipolarity/ polarizability of the medium whereas the azo group is slightly more responsive to polarity changes associated to the Lewis acidity and HBD-acidity of the medium. This holds true for compound **1** and **2a** but not for compound **2b** where the bulkiness of *beta*-CyD hinders any azobenzene-solvent direct interaction. In that case (**2b**) the azo group appears to have very similar sensitivity to solvent polarity to that that the FC group exhibits. On the other hand, both functional groups probed an intense PS effect by EG molecules however for each compound different extents in PS were probed. Compound **1**, again appeared to behave differently on a quantitative basis. The difference in probed extent PS between the azo and the FC group was the largest for **1** and dropped significantly in case of the *alpha*- or *beta*-CyD comprising [2]rotaxanes (compounds **2a**, and **2b**). Overall, compound **1**, exhibits a distinct dual sensing aptitude in terms of solutesolvent specific and non-specific effects as well as PS effects. The [2]rotaxanes have a rather attenuated dual sensing capacity presumably due to the presence of CyD which hinders the direct interaction of the azo-group (and its surrounding regions) with solvent molecules. As a result of the extended π-conjugation and the "shielding" effect of CyD the azo groups of compounds **2a** and **2b** tend to probe the same solvent polarity information as the FC group. It is important to mention that compound **1** clearly exhibits a dual solvatochromic behavior, however in water/EG BSMs the response of the azo group gets saturated to the value corresponding to neat EG very fast as one moves from neat water to neat EG (see **Table 4**). Nonetheless, as analyzed this corresponds to a special PS effect and taken together compound **1**, appears to be a very good polarity sensor candidate for future application mainly pertaining to polar media such

ð Þ¼ **2b** 0*:*046). Similar conclusions can be

Ioanna Deligkiozi<sup>1</sup> and Raffaello Papadakis1,2\*

1 Laboratory of Organic Chemistry, School of Chemical Engineering, National Technical University of Athens (NTUA), Athens, Greece

2 TdB Labs, Uppsala, Sweden

\*Address all correspondence to: rafpapadakis@gmail.com

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
