Solvatochromic effect studies on the absorption spectra of 4-((2-ethylphenyl)diazenyl)benzene-1,3-diol and 2-((2-ethylphenyl)diazenyl)benzene-1,3,5-triol molecules

doi:10.1016/j.ijhydene.2008.10.070

International Journal of Hydrogen Energy

Volume 34, Issue 12, June 2009, Pages 5255-5259

https://doi.org/10.1016/j.ijhydene.2008.10.070 Get rights and content

Abstract

The electronic absorption spectra of 4-((2-ethylphenyl)diazenyl)benzene-1,3-diol and 2-((2-ethylphenyl)diazenyl)benzene-1,3,5-triol molecules in the nine different solvent variable electronic characters have been recorded. The solvent dependent maximum absorption band (π–π* transitions) shifts, ν_max, were analyzed using a wide range of parameters such as refractive index, dielectric constant and Kamlet–Taft parameters [hydrogen bond donating ability (α) and hydrogen bond accepting ability (β)]. The electronic transitions are assigned and the solvent-induced spectral shifts have been analyzed in relation to the different solute–solvent interaction mechanism using computational chemistry. The intermolecular interaction types in the azobenzene derivatives solutions have been established on the basis of a multiple linear regression analysis. The fitting coefficients obtained from this analysis allowed us to estimate the contribution of each type of interactions to the total spectral shifts in the studied solutions.

Introduction

Azoaromatic compounds have attracted intensive attention due to the widespread range of applications in dye stuff industry, being photo aligning substrates for liquid crystals, photorefractive media, acid-base, redox and metallochrome indicators, optical actuators, optical storage media, catalytic in reactions of photo catalytic degration under solar light, etc. [1], [2], [3], [4], [5], [6], [7], [8]. Performing studies on photoluminescence and absorption spectroscopy of azo dyes can provide useful information for obtaining improvement in solar energy [9].

Solvents play an important role in physical and chemical processes [10], [11]. Their effect is closely related to the nature and extent of solute–solvent interactions developed locally in the immediate vicinity of solutes. One key approach to understand solvent effects is solvatochromism, the solvent-induced changes in the electronic transition of solutes. The solvent effect on the UV–vis. spectra of some azo compounds has been previously studied [4], [12], [13], [14], [15].

Solvent–solute interactions are determined by electronic and nuclear solvent polarization and they can be described by functions of the refractive index n, f(n) = (n² − 1)/(n² + 1), or (2n² − 1)/(n² + 1), and electric permittivity ɛ, f(ɛ) = (ɛ − 2)/(2ɛ + 1), or (ɛ − 1)/(ɛ + 2). All these functions can have different influences on the electronic absorption spectra that manifest in sign and magnitude, giving information on the intermolecular interactions in solutions [16].

Specific interactions can be present in solutions, the most important ones being hydrogen bondings [16], [17]. Their influence on the absorption spectra is very important, depending on whether the solvent molecules can act as donors or acceptors in the formation of hydrogen bondings with the solute molecules.

In this work two azobenzene derivatives (Fig. 1) were prepared and ultraviolet–visible absorption spectra have been recorded in nine solvents to study the influence of the solvents and to examine the effect of molecular structure on their absorption spectra. A careful analysis of the obtained data using statistical techniques showed that the solvatochromism correlates to the identity of substituent and solvent parameters as well. One aim of the present work is to discuss the effect of pure solvent on the UV–vis. spectra data of AZO1 and AZO2. The solvents are selected to have a wide variety of solute parameters.

Section snippets

Materials and experimental methodology

In this present study, 4-((2-ethylphenyl)diazenyl)benzene-1,3-diol and 2-((2-ethylphenyl)diazenyl)benzene-1,3,5-triol (Fig. 1) compounds were synthesized and the chemical structure of these molecules were confirmed with ¹³C NMR, ¹H NMR, FT-IR and UV spectroscopy methods by Aksu and Yıldırım [18], [19].

The solvents used of spectrophotometric grade and purchased from Sigma-Aldrich. The 99.9% pure solvents were used without extra purification. Each solutions were prepared as 6.4 × 10⁻⁴ M.

Result and discussion

The electronic absorption spectra of studied azobenzene derivatives were recorded in different solvents and relevant data were collected in Table 1. The electronic absorption spectra of AZO1 and AZO2 are shown in Fig. 2, Fig. 3, respectively. The electronic absorption spectra of studied AZO1 and AZO2 compounds in chloroform are depicted in Fig. 4.

Azoaromatic compounds usually exhibit a low intensity n–π* absorption band in the visible range of the spectrum and a high intensity π–π* band in the

Conclusion

We have demonstrated that a solvatochromic equation with four solvatochromic parameters f(ɛ), f(n), β and α can be used to evaluate the effects of both types of hydrogen bonding and of the solvent dipolarity/polarizability. Coefficients C₁ and C₂ determine the strength of the universal forces, while C₃ and C₄ coefficients characterize the strength of the specific interactions of the analyzed compounds. The spectral shifts of π–π* band of azoaromatic compound in solutions are mainly controlled

Acknowledgement

We are grateful to Eskişehir Osmangazi University Research Fund Committee for the financial support to this work via the Research Projects Numbers 200819015 and Hacettepe University Research Fund Committee (Projects Numbers G-01G011).

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