SPECTRAL INVESTIGATION OF TRIPHENYLFORMAZAN DERIVATIVES IN ULTRAVIOLET LIGHT

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1 CONDENSED MATTER SPECTRAL INVESTIGATION OF TRIPHENYLFORMAZAN DERIVATIVES IN ULTRAVIOLET LIGHT CLAUDIA NĂDEJDE 1, DORINA CREANGĂ 1, ELENA FILIP, DANA-ORTANSA DOROHOI 1 1 Faculty of Physics, Al. I. Cuza University, 11A Blvd. Carol I, , Iaºi, Romania, nadej_dia@yahoo.com, dorinacreanga@yahoo.com Faculty of Chemistry, Al. I. Cuza University, 11A Blvd. Carol I, , Iaºi, Romania Received September 5, 008 Four triphenylformazan derivatives were studied in various solvents aiming to reveal the types of intermolecular interactions. Solvent influence on UV absorption band was analyzed using graphs of spectral shift versus functions of solvent macroscopic parameters. The dominancy of dispersive interactions was evidenced, as well as some specific interactions. The HyperChem algorithms allowed getting additional data regarding microscopic parameters of triphenylformazans. Key words: triphenylformazans, solute-solvent interactions, ultraviolet band, microscopic parameters. 1. INTRODUCTION The solvent effect on the electronic absorption spectra of some triphenylformazan derivatives was revealed in the frame of this study. Binary solutions in different solvents were prepared, in order to reveal the nature of the solute-solvent interactions [1]. The solute molecules can interact with solvent ones through orientation, induction and/or dispersion forces (universal interactions), as well as by specific interactions. All types of Van der Waals interactions depend on the microscopic parameters of the solute molecule, such as the dipole moment (), polarizability () etc. The solvent effect can result in changes of the molecular energetic levels, which usually lead to electronic band shifts in the frequency scale [ 4], depending on the solvent macroscopic parameters like the refractive index (n) and dielectric permittivity (). In agreement with Bakhshiev s theoretical model [5], the wave number shift of the electronic absorption band, for a spectrally active molecule passing from the gaseous ( g ) to liquid phase ( s ), is given by the following equation: Paper presented at the 9th International Balkan Workshop on Applied Physics, July 7 9, 008, Constanþa, Romania. Rom. Journ. Phys., Vol. 54, Nos. 7 8, P , Bucharest, 009

2 650 Claudia Nãdejde et al., (1) s The proposed equations that describe the solvent influence upon electronic absorption band frequency are too complex for practical purpose: orientationinduction dispersion dinamic ij ij ij ij g, () n 1 i i j cos 1 n 1 i j 1 ij n n hcr3 n hcr3 n n 1 n C 1 3 C 4, n n where ij is the spectral shift between the theoretical frequencies corresponding to the i-j electronic transition, h Planck s constant, c light velocity in free space, n refractive index, dielectric permittivity and the microscopic parameters of the dissolved molecules: i,j permanent dipolar moments, the angle between dipolar moments, r molecular mean radius. Some approximations are commonly used (i.e. n 1 1 ), in order to express the n frequency shifts related to the macroscopic solvent parameters such as refractive index (n) and dielectric permittivity (). Thus, Bakhshiev s equation becomes: (3) where: n n n calc C C C C, (4) n n n C C cos,, hcr hcr i i j i j 1 C II i j i j hc f 3 C 3 4 hcr I 8 3 i Ij m ghcr,,, (5) are constants that depend on the microscopic parameters of the dissolved molecules: i,j permanent dipolar moments, the angle between dipolar moments, r molecular mean radius, ij, are the polarizabilities corresponding to the ground state, respectively the excited state, I i and I j are the ionization potentials, f is the oscillator strength, m is the molecular weight of the spectrally active molecule and g is the frequency of the electronic transition of the solute molecule in the gaseous state. Based on relation (4), the nature of solute-solvent intermolecular interactions can be interpreted. In the following, is presented the

3 3 Spectral investigation of triphenylformazan derivatives 651 analysis of the solvent effect on the ultraviolet electronic absorption spectra of triphenylformazans. The study of formazan derivatives is related to their role in redox processes involved in some microorganism metabolism. Triphenylformazan (TPF) is a substance produced after the reduction of triphenyl-tetrazolium chloride (TTC), used mainly as an indication of dehydrogenase activity, essential in cell metabolism.. MATERIALS AND METHODS The following formazan derivatives (Fig. 1) have been used as spectrally active molecules in binary solutions with various solvents, tabled below (Table 1): triphenylformazan (F1); N-(carboxy 4 phenol) N phenyl C phenylformazan (F), N-(nitro 4 phenyl) N phenyl C (3 nitrophenyl) formazan (F3), N-(carboxy phenyl) N phenyl C (3 nitrophenyl) formazan (F4). A number of thirty-three solvents were investigated in binary solutions, with various physic-chemical properties different values of the refractive index (n) and dielectric permittivity () (Table 1), with each formazan derivative. Investigations were carried out by means of spectrophotometric methods, using a double beam spectrophotometer type Shimadzu UV-1700 Pharma Spec with quartz cells of 1 cm width. Light absorption measurements upon the first maximum frequency (wavenumber) in ultraviolet band provided the quantitative data. Fig. 1 The chemical structure of triphenylformazan derivatives. (F1): triphenylformazan; (F): N-(carboxy 4 phenol) N phenyl C phenylformazan; (F3): N-(nitro 4 phenyl) N phenyl C (3 nitrophenyl) formazan; (F4): N-(carboxy phenyl) N phenyl C (3 nitrophenyl) formazan.

4 65 Claudia Nãdejde et al. 4 Table 1 The solvent macroscopic parameters No. Solvent n No. Solvent n 1 Dioxane , Dichloro-propane Carbon tetrachloride , Dichloro-ethane Benzene n-hexyl alcohol p-xylene Phenyl carbinol , 3, 5 Trimethyl-benzene Cyclohexanol Toluene n-amyl alcohol O-Xylene n-butanol Trichloroethylene Iso-butyl alcohol Anisole Iso-propyl alcohol , Dibromo-ethane n-propyl alcohol Ethyl-ether , 3 Butane diol Trichloromethane , Propane diol n-butyl acetate Benzonitrile Bromo-benzene Ethanol Ethyl-acetate Acrylonitrile Methyl-acetate Acetonitrile Dichloro-methane The spectral shifts were statistically analyzed using linear regression approach, in order to determine significant correlations with solvent parameters. The interpretation of intermolecular interactions solute-solvent can be used to obtain the microscopic parameters of the formazan derivatives. The obtained values of correlation coefficient (R) were higher than 0.9 in all cases. 3. RESULTS AND DISCUSSIONS The electronic absorption spectra of the studied compounds were recorded in the chosen solvents. The position and intensity of the UV band at 33,000 cm 1 (in ethanol) do not change in the protonation process (Fig. ), supporting the presumption that it can be assigned to * transitions [6 7]. Small aliquots of sulfuric acid were added with the goal of UV band assessment either to n * or to * transitions; the non-significant changes of UV band intensity and position, suggested that, in the corresponding transition, no free (non-participant) n-type electron is involved that could bond protons provided by sulfuric acid. A bathochromic shift was noticed for all formazan derivatives to the increase of solvent polarity, suggesting a stronger stabilization of the excited state compared to the ground state (Fig. 3).

5 5 Spectral investigation of triphenylformazan derivatives 653 Fig. The electronic absorption bands in ethanol (continuous line) and ethanol with sulfuric acid aliquots (dashed line) for F1 and F4. Fig. 3 The wavenumber maxima spectral shifts of the binary solutions with F1 and F4 triphenylformazan derivatives in the ultraviolet range. The solvent influence on the maximum frequency of the electronic absorption spectra, in the ultraviolet range, was analyzed using mathematical correlations between the spectral shifts and solvent macroscopic parameters; based on Bakhshiev theoretical model, the differences between experimental data and calculated ones are further discussed. For F1 and F3 molecules, the plots of exp versus f(n): f( n) n n 1, (5) in Figs. 4 5 are presented. No correlation between experimental wave number and the dielectric permittivity was found. Two straight lines with almost the same slope (Table ) were obtained for F1 (Fig. 4) following the application of less square method, suggesting the dominancy of dispersive type interactions [5]. The distance between the line grouping non polar solvents (squares) and the one grouping mostly polar ones (circles) is of about 0 cm 1, being a measure of the specific supplementary interactions corresponding to polar solvents.

6 654 Claudia Nãdejde et al. 6 Fig. 4 Experimental wave number versus f(n) in the case of F1. It is possible that specific interactions occur between F1 and alcohol like solvents, with the participation of nitrogen atoms from F1 structure. In the case of F3, though the dependence of exp on f(n) also indicated that the dispersive interactions are dominant within F3 solutions, the slopes of the two lines (Fig. 5) are differing with about 1,00, possibly related to the fact that the solvent grouping is not the same as for F1. The explanation needs to be based on the F3 structure which is more asymmetrical than that of F1, due to the NO atom groups substituted in non-symmetrical positions to the F1 skeleton. Specific interactions with HO groups from alcohols might be located at the level of nitrogen atoms belonging to the main molecular skeleton, since the N Fig. 5 Experimental wave number versus f(n) in the case of F3.

7 7 Spectral investigation of triphenylformazan derivatives 655 atoms could be partially pozitivated following electron cloud migration in the frame of resonance structures of formazan derivatives. But in the case of F1 and F3 the specific interactions with alcohols might be non-significant due to the possible concurrent interactions represented by intramolecular hydrogen bonds developed with the participation of COOH side groups (missing in the case of F1 and F3) since these ones could rotate toward the nitrogen atoms. In Figs. 6 7, the dependence of exp on f(n) for F and F4 is represented. As in the previous cases, for F as well as for F4, the relationship between exp and f(n) indicates the presence of dispersion interactions in the binary solutions of formazans. The F and F4 molecules are similar, being derived from F1 by the substitution of nitro atom group and also the substitution of carboxyl group in meta and respectively para position. Hydrogen bond could also occur between the formazans nitro groups and the hydrogen from alcohol like molecules, generating some specific interactions but not as strong as in the case of F3. The F and F4 similar structures are spatially arranged so that they oppose sterically to the influence of solvent upon the central nitrogen atoms which may explain the stability of carboxy-derivatives in (weak or strong) acid medium. Though the calculated polarizabilities are almost the same we believe that the higher dipole moment of F4 compared to F can explain the higher slope of the calculated straight line in the representation exp versus f(n) (Tables and 3). It is the OH group that possibly interacts by hydrogen bonds with F1-F4 molecules. This means supplementary shift of the studied electronic transitions when compared with universal interaction effects. The hydrogen bond could be located at the level of the nitrogen atoms present in the main structure of triphenylformazan. Fig. 6 Experimental wave number versus f(n) in the case of F.

8 656 Claudia Nãdejde et al. 8 Fig. 7 Experimental wave number versus f(n) in the case of F4. Table Intermolecular interaction parameters calculated for formazan molecules from the experimental data Parameter F1 F F3 F4 Slope ; ; Ordinate cut [cm 1 ] 34770; ; Table 3 Microscopic parameters of the formazan derivatives Parameter F1 F F3 F4 Dipole moment [D] Polarizability 10 4 [cm 3 ] Molecular volume V [A 3 ] Molecular mass M [u.a.m.] Additional complementary information on the hydrogen bond localization and strength could be provided by vibration spectra the goal of our future experimental project. Taking into account the microscopic parameters calculated for F1 and F3, by applying the semi-empirical molecular orbital calculation program HyperChem, PM3 method, one might say that the higher polarizability and mainly the considerably higher dipole moment of F3 comparatively to F1 can be also related to the occurrence of specific interactions (Table 3). Similar behavior was found for the visible absorption band (the results presented in a submitted paper were communicated at the 4 th International

9 9 Spectral investigation of triphenylformazan derivatives 657 Conference Physics of Liquid Matter: Modern Problems May 008, Kiev, Ukraine). Theoretical evaluation of solvent effects on the electronic absorption spectra of the studied molecules is important not only from the chemical point of view but also from practical use: for elucidating the mechanisms of solvatochromic shifts observed for organic and biological molecules. 4. CONCLUSION The absorbtion band in the ultraviolet range presents a bathochromic shift when passing from nonpolar solvents to polar ones while the position and intensity do not change during the protoning process, allowing the assigning to * transitions. In F1 F4 solutions, the universal interaction of dispersion type are the main ones, while the contribution of orientation-induction interactions can be neglected. The microscopic parameters of the spectrally active molecule in the ground state calculated with HyperChem soft, could be related to the differences evidenced between the four graphs exp versus f(n) corresponding to the four formazan derivatives analyzed in this paper. REFERENCES 1. S. A. Lee, S. Hotta, F. Nakanishi, Spectroscopic Characteristics and Intermolecular Interactions of Thiophene/Phenylene Co-Oligomers in Solutions, J. Phys. Chem. A, 104(9), (000).. Y. Marcus, The Properties of Solvents, Publisher: John Willey & Sons Inc., W. Linert, Highlights in Solute-Solvent Interactions, Publisher: Springer Verlag, Ch. Reichardt, Solvents and Solvent Effects in Organic Chemistry, Publisher: John Willey & Sons Inc, N. G. Bakhshiev, Intermolecular repulsion forces and optical spectra of molecules in solutions, Optics and Spectroscopy, 7(1), (199). 6. D. O. Dorohoi, D. Iancu, G. Surpateanu, The Influence of the Solvent on the Electronic Absorption Spectra of Some Pyridinium-Ylids, Sci. An. Al. I. Cuza Univ. Iasi, Section I, T7 (1981). 7. D. O. Dorohoi, Electric dipole moments of the spectrally active molecules estimated from the solvent influence on the electronic spectra, J. Mol. Struct., (3), 86 9 (006). 8. I. A. Rusu, S. Filoti, D. O. Dorohoi, M. Toma, Electric dipole moments in the excited states determined by means of spectral methods, J. Opt. Adv. Mat., 8(5), (006).