Tautomerism in 8-(phenyldiazenyl)quinolin-5-ol: An attempt for pH activated rotary switch
Graphical abstract
Introduction
The tautomerism of azo dyes and especially – azonaphthols, is a well-known phenomenon, influencing their stability and colour [1,2]. Among them, the 4-(phenyldiazenyl)naphthalen-1-ol (1, Scheme 1) is perhaps one of the most studied tautomeric systems. Being discovered almost 140 years ago in a pure chemical manner [3,4], it represents, even now, a challenging system to study or to model with respect to structural and environmental effects on the position of the tautomeric equilibrium [1,2,[5], [6], [7], [8], [9], [10]]. Compound 1 always exists as an azo-hydrazone tautomeric mixture and the tautomeric ratio (quantitatively defined as a constant KT, KT = [H]/[A]) is very sensitive to the solvent environment and less - to the temperature [[11], [12], [13]]. Recently it has been used as a successful platform for the development of new systems, exploiting controlled proton transfer for signal conversion and molecular sensing [[14], [15], [16]]. This was achieved by the implementation of a mediator - host (nitrogen-containing unit, crown ethers or similar macrocyclic receptors), which transfers a signal from the external stimuli to the tautomeric backbone. These structural modifications come to answer the need for a single tautomeric form in the sensing/signaling systems, being able, under suitable stimuli, to switch fully to the other tautomer.
The stability of azo compounds and their tautomerism make them suitable targets for new switching systems as the efforts are now directed to dyes, existing as a single tautomer in the solution and being able fully to convert upon changing the external stimuli. In this context, hydrazone based compounds are suitable architectures for chemically activated configurational rotary switches [17,18]. Furthermore, quinoline based hydrazones are proven to be appropriate molecular switch prototypes induced by pH change [19].
Quinoline-based compounds are widely used in the synthesis of colorants, especially azo dyes. Among them, azo dyes obtained from hydroxyl-substituted quinolines have been widely studied [[20], [21], [22]]. These dyes are recognized as biologically active agents [23], while some of them are utilized as chemosensors for anion detection [24] and corrosion inhibitors [25]. Quinoline-based dyes, especially 8-hydroxy substituted quinolines, represent renowned structures in coordination chemistry due to their chelating capacity towards metal ions [26,27]. Such complexes possess luminescent properties that enable their application as promising materials for multilayer light-emitting devices (OLEDs) [28]. The azo-hydrazone tautomerism in azo dyes, derived from hydroxyl-substituted quinolines, is also discussed [[29], [30], [31], [32], [33], [34]].
The 8-hydroxyquinoline derivatives need special attention, due to the possible involvement of the 8-OH group in an intramolecular hydrogen bond with the nitrogen atom of the quinoline ring as well as intermolecular hydrogen bonds with the N atom of an adjacent quinoline molecule [35], which influences the tautomeric state of the system. Heterocyclic and carbocyclic dyes based on this heterocycle exist as azo tautomers in the solid state, while in N,N-dimethylformamide (DMF) and dimethylsulfoxide (DMSO) these dyes exhibit azo-common anion equilibrium [29,31]. On the other hand, some authors have observed azo-hydrazone tautomerism of a particular 8-hydroxy substituted azoquinoline dyes in some dipolar aprotic and basic solvents, while in nonpolar and proton-donor solvents dyes adopt an azo form [30,33]. Structural investigations of 4-hydroxy-2-quinolone (2-hydroxyquinoline-4-one) based azo dyes in the solutions show that they appear as two hydrazone-keto forms that form strong intramolecular hydrogen bonds with the corresponding keto group [17,32].
While 2- and 8-hydroxyquinolines have been frequently used in the synthesis of various azo dyes, 5-hydroxyquinoline, to our best knowledge, has not been used. Although the synthesis of 8-(phenyldiazenyl)quinolin-5-ol (2) was reported using a different synthetic pathway [36], its tautomerism has never been studied. It gives interesting possibilities for additional stabilization due to intramolecular hydrogen bonding and shift of the equilibrium upon the change of pH (Scheme 2). Therefore, in the current paper, we report a new synthetic pathway and in-depth investigation of the tautomerism of 2. To our best knowledge, this is the first study of the tautomerism and spectral properties of 8-(phenyldiazenyl)quinolin-5-ol by using a combined experimental and theoretical approach. For quantitative elucidation of the solvent's effects on the position of absorption spectra, the concept of linear solvation energy relationships (LSER) is used. Furthermore, the possibility of using 2 as a pH stimulated rotary switch is investigated.
Section snippets
Materials and measurements
All reagents were purchased from Fluka, Aldrich and Acros Organics and were used without purification. Solvents used for UV–Vis analysis were of spectrophotometric grade. The melting point was obtained on the melting point system Stuart SMP30. FT-IR (Fourier transform infrared spectroscopy) spectrum of 2 was obtained on a Nicolet™ iS™ 10 FT-IR Spectrometer (Thermo Fisher SCIENTIFIC) spectrometer with Smart iTR™ Attenuated Total Reflectance (ATR) Sampling accessories in the range 500–4000 cm−1
Spectral characterization
Possible neutral and ionized forms of compound 2 are presented in Scheme 2. ATR FTIR spectrum of the dye 2 suggests that the dye adopts the azo form in the solid state (A form). Characteristic vibrations originating from the quinoline ring are observed at 1628 and 1578 cm−1 and are ascribed to stretching vibrations of CN imino and CC groups, respectively [52]. The band located at 1333 cm−1 is attributed to the in-plane-bending of OH group, while the broad signal at 3252 cm−1 corresponds to the
Conclusions
Tautomerism and spectral behavior of 8-(phenyldiazenyl)quinolin-5-ol are investigated in depth by combining experimental and theoretical approaches. The study involves a neutral molecule as well as its ionized forms. ATR FTIR spectrum of the dye suggests the existence of an azo form in the solid state. The spectral behavior of the investigated dye in solutions substantially differs from the naphthalene analog, 4-(phenyldiazenyl)naphthalen-1-ol and implies that the dye under investigation solely
CRediT authorship contribution statement
Jelena Lađarević: Investigation, Writing - original draft, Writing - review & editing. Dušan Mijin: Investigation, Validation, Writing - original draft, Writing - review & editing. Liudmil Antonov: Conceptualization, Methodology, Software, Writing - original draft, Writing - review & editing.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
Authors would like to acknowledge the financial support from the Ministry of Education, Science and Technological Development of the Republic of Serbia under Contract No.451-03-68/2020-14/200135 (J.L., D.M.) and from Bulgarian National Science Fund under the project MolRobot DN09/10 (L.A.).
References (59)
Azo-hydrazone tautomerism in azo dyes. I. A comparative study of 1-phenylazo-2-naphthol and 1-phenylazo-2-naphthylamine derivatives by electronic spectroscopy
Dyes Pigments
(1981)- et al.
Azo-hydrazone tautomerims of hydroxyazo compounds - a review
Dyes Pigments
(1982) - et al.
Quantitative analysis of azo-quinonehydrazone tautomeric equilibrium
Dyes Pigments
(1989) - et al.
A study of Solvatochromism in diazonium coupling products of 6-flouro 4-hydroxyl-2-quinolone
J Mol Liq
(2011) - et al.
Synthesis and investigations of the absorption spectra of hetarylazo disperse dyes derived from 2,4-quinolinediol
Dyes Pigments
(2006) - et al.
Novel azo dyes derived from 8-methyl-4-hydroxyl-2-quinolone: synthesis, UV–vis studies and biological activity
Chin Chem Lett
(2013) - et al.
8-Hydroxyquinoline based push-pull azo dye: novel colorimetric chemosensor for anion detection
J Mol Struct
(2017) - et al.
Thermal properties, geometrical structures, antimicrobial activity and DNA binding of supramolecular azo dye complexes
J Mol Liq
(2016) - et al.
Synthesis and spectroscopic properties of new hetarylazo 8-hydroxyquinolines from some heterocyclic amines
Dyes Pigments
(2008) - et al.
Azo-8-hydroxyquinoline dyes: the synthesis, characterizations and determination of tautomeric properties of some new phenyl- and heteroarylazo-8-hydroxyquinolines
J Mol Liq
(2014)
Synthesis, spectral features and biological activity of some novel hetarylazo dyes derived from 8-chloro-4-hydroxyl-2-quinolone
Spectrochim Acta A
Synthesis, spectroscopic characteristics, dyeing performance and TD-DFT study of quinolone based red emitting acid azo dyes
Dyes Pigments
Supramolecular structures and stereochemical versatility of azoquinoline containing novel rare earth metal complexes
Spectrochim Acta A
Thermodynamic cycles and the calculation of pKa
Chem Phys Lett
Facile and regioselective synthesis of poly(5-hydroxyquinoline)
React Funct Polym
Role of the bifurcated intramolecular hydrogen bond on the physicochemical profle of the novel azo pyridone dyes
Dyes Pigments
Color chemistry: syntheses, properties, and applications of organic dyes and pigments
Azo dyes. Organic chemistry in colour
Ueber Phenylhydrazinderivate des α- und β-Naphtochinons. Identität des α-Derivats mit dem Azoderivat des α-Naphtols
Ber Dtsch Chem Ges
Tautomerism: introduction, history, and recent developments in experimental and theoretical methods
Developments in the chemistry and technology of organic dyes
Chemometric models for quantitative analysis of tautomeric schiff bases and azo dyes
Curr Org Chem
Tautomerism in hydroxynaphthaldehyde anils and azo analogues: a combined experimental and computational study
J Phys Chem A
Tautomerism in azo and azomethyne dyes: when and if theory meets experiment
Molecules
Temperature dependent absorption spectroscopy of some tautomeric azo dyes and Schiff bases
J Chem Soc Perk T
Exploiting tautomerism for switching and signaling
Angew Chem Int Ed
Controlled tautomerism: is it possible?
Tautomerism as primary signaling mechanism in metal sensing: the case of amide group
Beilstein J Org Chem
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