- Email: [email protected]
TD-DFT calculations
Accepted Manuscript New heterocyclic green, blue and orange dyes from indazole: Synthesis, tautomerism, alkylation studies, spectroscopic characterization and DFT/TD-DFT calculations Soodabeh Poorhaji, Mehdi Pordel, Shirin Ramezani PII:
S0022-2860(16)30414-8
DOI:
10.1016/j.molstruc.2016.04.078
Reference:
MOLSTR 22492
To appear in:
Journal of Molecular Structure
Received Date: 18 November 2015 Revised Date:
1 April 2016
Accepted Date: 25 April 2016
Please cite this article as: S. Poorhaji, M. Pordel, S. Ramezani, New heterocyclic green, blue and orange dyes from indazole: Synthesis, tautomerism, alkylation studies, spectroscopic characterization and DFT/TD-DFT calculations, Journal of Molecular Structure (2016), doi: 10.1016/ j.molstruc.2016.04.078. 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.
ACCEPTED MANUSCRIPT
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Graphical Abstract
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New heterocyclic green, blue and orange dyes from indazole: Synthesis, tautomerism, alkylation studies,–spectroscopic characterization and DFT/TD-
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DFT calculations Soodabeh Poorhaji, Mehdi Pordel* and Shirin Ramezani
Department of Chemistry, Mashhad Branch, Islamic Azad University, Mashhad, Iran
SC
*Corresponding author. Tel.: +98 0511 8414182; fax: +98 0511 8424020. E-mail: [email protected]
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Abstract— Tautomerism and alkylation studies on the green intermediate 2-(5-hydroxyimino-1methyl-4,5-dihydro-1H-4-indazolyliden)-2-phenylacetonitrile led to the synthesis of new heterocyclic green, blue and orange dyes in high yields. The structures of all newly synthesized compounds were confirmed by spectral and analytical data. The optical properties of the dyes were spectrally characterized by using a UV-vis spectrophotometer and results show that they
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exhibited interesting photophysical properties. Solvent effects on the absorption spectra of these dyes have been studied and the absorption band in polar solvents undergoes a red shift. Density
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functional theory calculations of the dyes were performed to provide the optimized geometries and relevant frontier orbitals. Calculated electronic absorption spectra were also obtained by
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time-dependent density functional theory method.
Keywords: 5-Nitro-1H-indazole; Heterocyclic dyes; Optical properties; Density function theory calculations; Tautomerism
1
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1. Introduction Donor–acceptor (D–A) heterocyclic dyes are among the most important conjugated organic
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materials, and have attracted much academic and technological research interest. In these compounds the electron-donating and electron-accepting groups are connected through a πconjugated linker. Tuning different donor moiety or acceptor moiety in a D–A molecule would modify its physical and chemical properties. They have been evaluated and employed in the new
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areas of information-recording materials [1], information-display media [2], or optoelectronic
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devices [3]. These dyes can also be applied to organic photoconductors [4], solar-energy utilizations [5], sensitizers [6], biomedical probe [7], photo-catalysts [8], and so on. Furthermore, donor–acceptor heterocyclic dyes have been used extensively in the preparation of disperse dyes with outstanding dischargeability on cellulose acetate. These dyes are characterized also by having generally excellent brightness and high extinction coefficients. These new trends of dye
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chemistry have been recently developed and these classes of dyes are of significant importance in high-technology industries.
On the other hand, indazole scaffolds show interesting biological properties, such as anti-
EP
depressant [9], anti-inflammatory [10], anti-tumor [11] and anti-HIV activities [12]. Recently
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indazole nucleus become of interest as a key moiety of dyes [13] and fluorescent compounds [14–17].
In continuation of our previous study on the synthesis of new green dyes from indazole [13], in current work, we have synthesized some new green, blue and orange dyes via alkylation and oxidation studies on the green intermediate 2-(5-hydroxyimino-1-methyl-4,5-dihydro-1H-4indazolyliden)-2-phenylacetonitrile in high yields. In addition, tautomerism, optical properties and DFT calculations of the dyes have also been examined.
2
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2. Experimental 2.1. Materials
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Methanol, ethyl acetate (EtOAc), tetrahydrofuran (THF), acetonitrile, dichloromethane (DCM), N,N-dimethylformamide (DMF), methyl iodide, dimethyl sulfate (DMS), potassium tert-
butoxide, tert-butanol and benzyl cyanide were purchased from Merck. Potassium hydroxide was
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purchased from Sigma-Aldrich. All solvents were dried according to standard procedures. Compounds 1 and 3 were synthesized as in literature [18, 13].
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2.2. Equipment
Absorption spectra were recorded on a Varian Cary 50-bio UV–visible spectrophotometer. UV– vis scans were recorded from 200 to 800 nm. Melting points were measured on an Electrothermaltype-9100 melting-point apparatus. The IR (as KBr discs) spectra were obtained
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on a Tensor 27 spectrometer and only noteworthy absorptions are listed. The 13C NMR (100 MHz) and the 1H NMR (400 MHz) spectra were recorded on a Bruker Avance DRX-400 Fourier-transformer spectrometer in DMSO-d6 and CDCl3. Chemical shifts are reported in parts
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per million downfield from TMS as the internal standard; coupling constant J is given in hertz.
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The mass spectra were recorded on a Varian Mat, CH-7 at 70 eV. Elemental analysis was performed on a Thermo Finnigan Flash EA microanalyzer. All measurements were carried out at room temperature.
2.3. Computational methods DFT calculations have been performed with the Gaussian 98 software package [19] by using the B3LYP hybrid functional [20] and the 6-311++G (d,p) basis set. Firstly, geometry of the compounds 3, 4 and 5 was fully optimized in the MeOH solution. 3
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Here, one of self-consistent reaction field methods, the sophisticated Polarized Continuum Model (PCM) [21] has been used for investigation of the solvent effects. The PCM calculations have been performed in the MeOH solution and the zero-point corrections were considered to
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obtain energies. Based on the optimized geometries and using time-dependent density functional theory (TD-DFT) [22–24] methods, the electronic spectra of the compounds 3, 4 and 5 were predicted.
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2.4. Synthesis of 2-(1-methyl-5-nitroso-1H-indazol-4-yl)-2-phenylacetonitrile (4).
Compound 3 (5.0 g, 18 mmol) was heated 4 hr under reflux in EtOAC or other solvents such as
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CHCl3, MeCN and MeOH (80 mL). Also, dye 3 converts to 4 under the influence of visible light after 2 days in above mentioned solvents at rt. Furthermore, the process can catalyze in acidic media (pH 2-6, H2O-MeOH, 95:5) and takes place in less than 4 hours. After concentration the blue solution at reduced pressure, the precipitate was collected by
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filtration, washed with water and then air dried to give dark blue powder 4. More purification was achieved by recrystallization from acetone.
Yield (90%), mp 135-137 °C; 1H NMR (DMSO-d6) δ 4.21 (s, 3H, N-CH3), 6.54 (s, 1H, benzylic
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CH), 7.24–7.30 (m, 3H, Ar H), 7.33–7.37 (m, 2H, Ar H), 7.48 (d, J=9.5 Hz, 1H, Ar H), 8.53 (d, J=9.5 Hz, 1H, Ar H), 8.65 (s, 1H, Ar H); 13C NMR (DMSO-d6): δ 35.6, 36.7, 107.3, 112.3,
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125.8, 127.9, 131.0, 133.2, 133.8, 134.6, 143.5, 149.4, 151.0, 167.2; IR (KBr): 2340 cm-1 (CN), 1535 cm-1 (N=O). MS (m/z) 276 (M+). Anal. Calcd for C16H12N4O (276.3): C, 69.55; H, 4.38; N, 20.28. Found: C, 69.27; H, 4.36; N, 20.07. 2.5. Synthesis of 2-(1-methyl-5-nitro-1H-indazol-4-yl)-2-phenylacetonitrile (5). To a stirred solution of dye 4 (2.76 g, 10 mmol) in MeOH (10.0 mL) were added 30% H2O2 (5.5 mL, 21 mmol) at 60 °C. After the 4 h, the orange solution was diluted with H2O (50 mL), chilled
4
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and filtered, and then the solid was washed with H2O and air dried to give crude 5. Dye 5 was recrystallized from MeOH. Yield (85%), mp 156-159 °C; 1H NMR (DMSO-d6) δ 4.23 (s, 3H, NCH3), 6.61 (s, 1H, benzylic CH), 7.26–7.34 (m, 3H, Ar H), 7.37–7.40 (m, 2H, Ar H), 7.43 (d,
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J=9.5 Hz, 1H, Ar H), 8.61 (s, 1H, Ar H), 8.69 (d, J=9.5 Hz, 1H, Ar H); 13C NMR (DMSO-d6): δ 37.1, 39.6, 105.6, 110.1, 125.7, 125.9, 131.6, 133.5, 133.9, 134.2, 142.4, 149.4, 151.3, 167.6; IR (KBr): 2345 cm-1 (CN), 1335, 1545 cm-1 (NO2). MS (m/z) 292 (M+). Anal. Calcd for C16H12N4O2
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(292.3): C, 69.75; H, 4.14; N, 19.17. Found: C, 69.52; H, 4.11; N, 18.95.
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2.6. Synthesis of 5-(methoxyimino)-1-methyl-1H-indazol-4(5H)-ylidene)-2phenylacetonitrile (6).
To a green solution of dye 3 (1.4 g, 5 mmol) in acetonitrile (50 mL), dimethyl sulfate (DMS) (0.9 g, 7 mmol) and K2CO3 (5.5 g, 40 mmol) were added. The mixture was stirred for 12 h at rt and
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then poured into water. The product was extracted with CH2Cl2 (2×50 mL). The extract was dried (MgSO4), treated with charcoal and evaporated to give crude 6. More purification was achieved by recrystallization from MeOH-H2O (1:1).
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Yield (75%), mp 125-127 °C; 1H NMR (CDCl3) δ 4.21 (s, 3H, N-CH3), 4.31 (s, 3H, O-CH3), 7.33–7.37 (m, 2H, Ar H), 7.48 (d, J=9.5 Hz, 1H, Ar H), 7.55 (d, J=9.5 Hz, 1H, Ar H), 7.59–7.61
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(m, 2H, Ar H), 7.79 (t, J=8.0 Hz, 1H, Ar H), 8.21 (s, 1H, Ar H); 13C NMR (DMSO-d6): δ 36.3, 65.7, 108.8, 114.2, 121.6, 122.6, 125.0, 128.1,129.7, 130.8, 131.2, 135. 4, 145. 2, 153.5, 162.0; IR (KBr): 2220 cm-1 (CN). MS (m/z) 290 (M+). Anal. Calcd for C17H14N4O (290.3): C, 70.33; H, 4.86; N, 19.30. Found: C, 70.19; H, 4.83; N, 19.11.
2.7. Synthesis of 2-(1-methyl-5-nitroso-1H-indazol-4-yl)-2-phenylpropanenitrile (7).
5
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Methyl iodide (1.4 g, 10 mmol) and potassium tert-butoxide (1.12 g, 10 mmol) were added to a solution of compound 4 (2.76 g, 10 mmol) in tert-butanol (50 mL). After the mixture was stirred for 4 h at rt, it poured into water. The product was extracted with CH2Cl2 (2×40 mL). The extract
performed by recrystallization from n-hexane-EtOAc (1:1).
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was dried (MgSO4), treated with charcoal and evaporated to give crude 7. More purification was
Yield (60%), mp 131-134 °C; 1H NMR (CDCl3) δ 3.15 (s, 3H, CH3), 4.23 (s, 3H, N-CH3), 7.21–
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7.27 (m, 3H, Ar H), 7.34–7.38 (m, 2H, Ar H), 7.51 (d, J=9.5 Hz, 1H, Ar H), 8.49 (d, J=9.5 Hz, 1H, Ar H), 8.62 (s, 1H, Ar H); 13C NMR (CDCl3): δ 30.4, 35.5, 44.2, 107.9, 111.6, 126.5, 128.3,
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131.3 133.4, 133.9, 134.6, 143.2, 149.7, 151.2, 167.8; IR (KBr): 2345 cm-1 (CN), 1545 cm-1 (N=O). MS (m/z) 290 (M+). Anal. Calcd for C17H14N4O (290.3): C, 70.33; H, 4.86; N, 19.30. Found: C, 70.17; H, 4.82; N, 19.19.
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3. Results and discussion
3.1. Synthesis and Structure of the new dyes 4–7
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As depicted in Scheme 1, 1-methyl-5-nitro-1H-indazole (1) was prepared by reaction of 5-nitro1H-indazole with methyl iodide in DMF and KOH using literature method [18]. The reaction of
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1-methyl-5-nitro-1H-indazole with benzyl cyanide (2) led to the formation of key intermediate 2(5-hydroxyimino-1-methyl-4,5-dihydro-1H-4-indazolyliden)-2 phenylacetonitriles (3) via the nucleophilic substitution of hydrogen [25–27] in basic methanol solution in excellent yield (Scheme 1). The structure of dye 3 has been established by DFT calculations previously [13].
6
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When compound 3 was heated under reflux in EtOAC or other solvents such as CHCl3 and MeCN, new blue dye 4 was obtained in excellent yield (Scheme 2). The structure of the new synthesized compound 4 was deduced from their spectral and
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microanalytical data. For example, the IR spectrum of 4 showed a stretching vibration band at 1535 cm-1 indicating for N=O group. The 1H NMR spectrum of 4 showed three distinguished singlet signals at δ 4.21, 6.54 and 8.65 ppm for protons of methyl, benzyl and pyrazole ring
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respectively, a multiplet in the range of 7.24–7.35 ppm attributed to five aromatic protons of phenyl ring and two doublet signals at δ 7.48 and 8.53 ppm assignable to two aromatic protons
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H-4 and H-5 while the 13C NMR spectrum displayed a signal at δ 35.6 ppm confirming the presence of benzylic carbon. The mass spectrum of 4 showed the molecular ion peak at m/z 276 (M+) corresponding to the molecular formula C16H12N4O.
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Oxidation of blue dye 4 with 30% H2O2 in MeOH led to the formation of new orange dye 5 in
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high yield (Scheme 3). The structural assignments of compound 5 were based on the analytical and spectral data. For example, in the IR spectrum of 5, two strong absorption bands at 1335 and
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1545 cm-1 are assignable to nitro group. Furthermore, the mass spectrum of 5 showed the molecular ion peak at m/z 292 (M+) corresponding to the molecular formula C16H12N4O2.
7
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Conversion of dye 4 to dye 3 was also examined. The color of blue solution of dye 4 in KOH/MeOH was smoothly changed to green which indicates the formation of 3 anion (Dye 3 was precipitated after neutralization the solution with dilute HCl). However, these evidences
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prove that dyes 3 and 4 are not well enough stable and they can convert to each other in appropriate conditions.
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Alkylation of active protons of dyes 3 and 4 prevents from tautomerization of these dyes. Compound 3 was methylated by dimethyl sulfate (DMS) in K2CO3 and MeCN to give new green dye 5-(methoxyimino)-1-methyl-1H-indazol-4(5H)-ylidene)-2 phenylacetonitrile (6) at rt (Scheme 4). New blue dye 2-(1-methyl-5-nitroso-1H-indazol-4-yl)-2-phenylpropanenitrile (7)
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was also obtained from the reaction of dye 4 with methyl iodide in potassium tert-butoxide and tert-butanol in good yield (Scheme 4). All the newly synthesized dyes have been characterized by elemental analysis and spectroscopic data. The spectral details of all these are given in
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experimental section.
3.2. Optical properties
The new dyes 4–7 were spectrally characterized by using a UV-vis spectrophotometer and the wavelength range of spectrophotometer was 200–800 nm. Fig. 1 shows the visible absorption spectrum of compounds 3 and 4–7 in dilute (2 × 10-6 M) methanol solution. Characteristics of absorption spectra for 3 and 4–7 in methanol are presented in Table 1. Values of extinction
8
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coefficient (ε) were calculated as the slope of the plot of absorbance vs concentration. Absorbance intensity and extinction coefficient (ε) in blue dye 4 were the biggest values. It should be emphasized that nitroso group is the strongest chromophore, being able to shift
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bathochromically absorption of given aromatic compound more than any other two-atom
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S0022-2860(16)30414-8
DOI:
10.1016/j.molstruc.2016.04.078
Reference:
MOLSTR 22492
To appear in:
Journal of Molecular Structure
Received Date: 18 November 2015 Revised Date:
1 April 2016
Accepted Date: 25 April 2016
Please cite this article as: S. Poorhaji, M. Pordel, S. Ramezani, New heterocyclic green, blue and orange dyes from indazole: Synthesis, tautomerism, alkylation studies, spectroscopic characterization and DFT/TD-DFT calculations, Journal of Molecular Structure (2016), doi: 10.1016/ j.molstruc.2016.04.078. 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.
ACCEPTED MANUSCRIPT
AC C
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Graphical Abstract
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New heterocyclic green, blue and orange dyes from indazole: Synthesis, tautomerism, alkylation studies,–spectroscopic characterization and DFT/TD-
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DFT calculations Soodabeh Poorhaji, Mehdi Pordel* and Shirin Ramezani
Department of Chemistry, Mashhad Branch, Islamic Azad University, Mashhad, Iran
SC
*Corresponding author. Tel.: +98 0511 8414182; fax: +98 0511 8424020. E-mail: [email protected]
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Abstract— Tautomerism and alkylation studies on the green intermediate 2-(5-hydroxyimino-1methyl-4,5-dihydro-1H-4-indazolyliden)-2-phenylacetonitrile led to the synthesis of new heterocyclic green, blue and orange dyes in high yields. The structures of all newly synthesized compounds were confirmed by spectral and analytical data. The optical properties of the dyes were spectrally characterized by using a UV-vis spectrophotometer and results show that they
TE D
exhibited interesting photophysical properties. Solvent effects on the absorption spectra of these dyes have been studied and the absorption band in polar solvents undergoes a red shift. Density
EP
functional theory calculations of the dyes were performed to provide the optimized geometries and relevant frontier orbitals. Calculated electronic absorption spectra were also obtained by
AC C
time-dependent density functional theory method.
Keywords: 5-Nitro-1H-indazole; Heterocyclic dyes; Optical properties; Density function theory calculations; Tautomerism
1
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1. Introduction Donor–acceptor (D–A) heterocyclic dyes are among the most important conjugated organic
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materials, and have attracted much academic and technological research interest. In these compounds the electron-donating and electron-accepting groups are connected through a πconjugated linker. Tuning different donor moiety or acceptor moiety in a D–A molecule would modify its physical and chemical properties. They have been evaluated and employed in the new
SC
areas of information-recording materials [1], information-display media [2], or optoelectronic
M AN U
devices [3]. These dyes can also be applied to organic photoconductors [4], solar-energy utilizations [5], sensitizers [6], biomedical probe [7], photo-catalysts [8], and so on. Furthermore, donor–acceptor heterocyclic dyes have been used extensively in the preparation of disperse dyes with outstanding dischargeability on cellulose acetate. These dyes are characterized also by having generally excellent brightness and high extinction coefficients. These new trends of dye
TE D
chemistry have been recently developed and these classes of dyes are of significant importance in high-technology industries.
On the other hand, indazole scaffolds show interesting biological properties, such as anti-
EP
depressant [9], anti-inflammatory [10], anti-tumor [11] and anti-HIV activities [12]. Recently
AC C
indazole nucleus become of interest as a key moiety of dyes [13] and fluorescent compounds [14–17].
In continuation of our previous study on the synthesis of new green dyes from indazole [13], in current work, we have synthesized some new green, blue and orange dyes via alkylation and oxidation studies on the green intermediate 2-(5-hydroxyimino-1-methyl-4,5-dihydro-1H-4indazolyliden)-2-phenylacetonitrile in high yields. In addition, tautomerism, optical properties and DFT calculations of the dyes have also been examined.
2
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2. Experimental 2.1. Materials
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Methanol, ethyl acetate (EtOAc), tetrahydrofuran (THF), acetonitrile, dichloromethane (DCM), N,N-dimethylformamide (DMF), methyl iodide, dimethyl sulfate (DMS), potassium tert-
butoxide, tert-butanol and benzyl cyanide were purchased from Merck. Potassium hydroxide was
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purchased from Sigma-Aldrich. All solvents were dried according to standard procedures. Compounds 1 and 3 were synthesized as in literature [18, 13].
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2.2. Equipment
Absorption spectra were recorded on a Varian Cary 50-bio UV–visible spectrophotometer. UV– vis scans were recorded from 200 to 800 nm. Melting points were measured on an Electrothermaltype-9100 melting-point apparatus. The IR (as KBr discs) spectra were obtained
TE D
on a Tensor 27 spectrometer and only noteworthy absorptions are listed. The 13C NMR (100 MHz) and the 1H NMR (400 MHz) spectra were recorded on a Bruker Avance DRX-400 Fourier-transformer spectrometer in DMSO-d6 and CDCl3. Chemical shifts are reported in parts
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per million downfield from TMS as the internal standard; coupling constant J is given in hertz.
AC C
The mass spectra were recorded on a Varian Mat, CH-7 at 70 eV. Elemental analysis was performed on a Thermo Finnigan Flash EA microanalyzer. All measurements were carried out at room temperature.
2.3. Computational methods DFT calculations have been performed with the Gaussian 98 software package [19] by using the B3LYP hybrid functional [20] and the 6-311++G (d,p) basis set. Firstly, geometry of the compounds 3, 4 and 5 was fully optimized in the MeOH solution. 3
ACCEPTED MANUSCRIPT
Here, one of self-consistent reaction field methods, the sophisticated Polarized Continuum Model (PCM) [21] has been used for investigation of the solvent effects. The PCM calculations have been performed in the MeOH solution and the zero-point corrections were considered to
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obtain energies. Based on the optimized geometries and using time-dependent density functional theory (TD-DFT) [22–24] methods, the electronic spectra of the compounds 3, 4 and 5 were predicted.
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2.4. Synthesis of 2-(1-methyl-5-nitroso-1H-indazol-4-yl)-2-phenylacetonitrile (4).
Compound 3 (5.0 g, 18 mmol) was heated 4 hr under reflux in EtOAC or other solvents such as
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CHCl3, MeCN and MeOH (80 mL). Also, dye 3 converts to 4 under the influence of visible light after 2 days in above mentioned solvents at rt. Furthermore, the process can catalyze in acidic media (pH 2-6, H2O-MeOH, 95:5) and takes place in less than 4 hours. After concentration the blue solution at reduced pressure, the precipitate was collected by
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filtration, washed with water and then air dried to give dark blue powder 4. More purification was achieved by recrystallization from acetone.
Yield (90%), mp 135-137 °C; 1H NMR (DMSO-d6) δ 4.21 (s, 3H, N-CH3), 6.54 (s, 1H, benzylic
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CH), 7.24–7.30 (m, 3H, Ar H), 7.33–7.37 (m, 2H, Ar H), 7.48 (d, J=9.5 Hz, 1H, Ar H), 8.53 (d, J=9.5 Hz, 1H, Ar H), 8.65 (s, 1H, Ar H); 13C NMR (DMSO-d6): δ 35.6, 36.7, 107.3, 112.3,
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125.8, 127.9, 131.0, 133.2, 133.8, 134.6, 143.5, 149.4, 151.0, 167.2; IR (KBr): 2340 cm-1 (CN), 1535 cm-1 (N=O). MS (m/z) 276 (M+). Anal. Calcd for C16H12N4O (276.3): C, 69.55; H, 4.38; N, 20.28. Found: C, 69.27; H, 4.36; N, 20.07. 2.5. Synthesis of 2-(1-methyl-5-nitro-1H-indazol-4-yl)-2-phenylacetonitrile (5). To a stirred solution of dye 4 (2.76 g, 10 mmol) in MeOH (10.0 mL) were added 30% H2O2 (5.5 mL, 21 mmol) at 60 °C. After the 4 h, the orange solution was diluted with H2O (50 mL), chilled
4
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and filtered, and then the solid was washed with H2O and air dried to give crude 5. Dye 5 was recrystallized from MeOH. Yield (85%), mp 156-159 °C; 1H NMR (DMSO-d6) δ 4.23 (s, 3H, NCH3), 6.61 (s, 1H, benzylic CH), 7.26–7.34 (m, 3H, Ar H), 7.37–7.40 (m, 2H, Ar H), 7.43 (d,
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J=9.5 Hz, 1H, Ar H), 8.61 (s, 1H, Ar H), 8.69 (d, J=9.5 Hz, 1H, Ar H); 13C NMR (DMSO-d6): δ 37.1, 39.6, 105.6, 110.1, 125.7, 125.9, 131.6, 133.5, 133.9, 134.2, 142.4, 149.4, 151.3, 167.6; IR (KBr): 2345 cm-1 (CN), 1335, 1545 cm-1 (NO2). MS (m/z) 292 (M+). Anal. Calcd for C16H12N4O2
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(292.3): C, 69.75; H, 4.14; N, 19.17. Found: C, 69.52; H, 4.11; N, 18.95.
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2.6. Synthesis of 5-(methoxyimino)-1-methyl-1H-indazol-4(5H)-ylidene)-2phenylacetonitrile (6).
To a green solution of dye 3 (1.4 g, 5 mmol) in acetonitrile (50 mL), dimethyl sulfate (DMS) (0.9 g, 7 mmol) and K2CO3 (5.5 g, 40 mmol) were added. The mixture was stirred for 12 h at rt and
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then poured into water. The product was extracted with CH2Cl2 (2×50 mL). The extract was dried (MgSO4), treated with charcoal and evaporated to give crude 6. More purification was achieved by recrystallization from MeOH-H2O (1:1).
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Yield (75%), mp 125-127 °C; 1H NMR (CDCl3) δ 4.21 (s, 3H, N-CH3), 4.31 (s, 3H, O-CH3), 7.33–7.37 (m, 2H, Ar H), 7.48 (d, J=9.5 Hz, 1H, Ar H), 7.55 (d, J=9.5 Hz, 1H, Ar H), 7.59–7.61
AC C
(m, 2H, Ar H), 7.79 (t, J=8.0 Hz, 1H, Ar H), 8.21 (s, 1H, Ar H); 13C NMR (DMSO-d6): δ 36.3, 65.7, 108.8, 114.2, 121.6, 122.6, 125.0, 128.1,129.7, 130.8, 131.2, 135. 4, 145. 2, 153.5, 162.0; IR (KBr): 2220 cm-1 (CN). MS (m/z) 290 (M+). Anal. Calcd for C17H14N4O (290.3): C, 70.33; H, 4.86; N, 19.30. Found: C, 70.19; H, 4.83; N, 19.11.
2.7. Synthesis of 2-(1-methyl-5-nitroso-1H-indazol-4-yl)-2-phenylpropanenitrile (7).
5
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Methyl iodide (1.4 g, 10 mmol) and potassium tert-butoxide (1.12 g, 10 mmol) were added to a solution of compound 4 (2.76 g, 10 mmol) in tert-butanol (50 mL). After the mixture was stirred for 4 h at rt, it poured into water. The product was extracted with CH2Cl2 (2×40 mL). The extract
performed by recrystallization from n-hexane-EtOAc (1:1).
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was dried (MgSO4), treated with charcoal and evaporated to give crude 7. More purification was
Yield (60%), mp 131-134 °C; 1H NMR (CDCl3) δ 3.15 (s, 3H, CH3), 4.23 (s, 3H, N-CH3), 7.21–
SC
7.27 (m, 3H, Ar H), 7.34–7.38 (m, 2H, Ar H), 7.51 (d, J=9.5 Hz, 1H, Ar H), 8.49 (d, J=9.5 Hz, 1H, Ar H), 8.62 (s, 1H, Ar H); 13C NMR (CDCl3): δ 30.4, 35.5, 44.2, 107.9, 111.6, 126.5, 128.3,
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131.3 133.4, 133.9, 134.6, 143.2, 149.7, 151.2, 167.8; IR (KBr): 2345 cm-1 (CN), 1545 cm-1 (N=O). MS (m/z) 290 (M+). Anal. Calcd for C17H14N4O (290.3): C, 70.33; H, 4.86; N, 19.30. Found: C, 70.17; H, 4.82; N, 19.19.
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3. Results and discussion
3.1. Synthesis and Structure of the new dyes 4–7
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As depicted in Scheme 1, 1-methyl-5-nitro-1H-indazole (1) was prepared by reaction of 5-nitro1H-indazole with methyl iodide in DMF and KOH using literature method [18]. The reaction of
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1-methyl-5-nitro-1H-indazole with benzyl cyanide (2) led to the formation of key intermediate 2(5-hydroxyimino-1-methyl-4,5-dihydro-1H-4-indazolyliden)-2 phenylacetonitriles (3) via the nucleophilic substitution of hydrogen [25–27] in basic methanol solution in excellent yield (Scheme 1). The structure of dye 3 has been established by DFT calculations previously [13].
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When compound 3 was heated under reflux in EtOAC or other solvents such as CHCl3 and MeCN, new blue dye 4 was obtained in excellent yield (Scheme 2). The structure of the new synthesized compound 4 was deduced from their spectral and
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microanalytical data. For example, the IR spectrum of 4 showed a stretching vibration band at 1535 cm-1 indicating for N=O group. The 1H NMR spectrum of 4 showed three distinguished singlet signals at δ 4.21, 6.54 and 8.65 ppm for protons of methyl, benzyl and pyrazole ring
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respectively, a multiplet in the range of 7.24–7.35 ppm attributed to five aromatic protons of phenyl ring and two doublet signals at δ 7.48 and 8.53 ppm assignable to two aromatic protons
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H-4 and H-5 while the 13C NMR spectrum displayed a signal at δ 35.6 ppm confirming the presence of benzylic carbon. The mass spectrum of 4 showed the molecular ion peak at m/z 276 (M+) corresponding to the molecular formula C16H12N4O.
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Oxidation of blue dye 4 with 30% H2O2 in MeOH led to the formation of new orange dye 5 in
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high yield (Scheme 3). The structural assignments of compound 5 were based on the analytical and spectral data. For example, in the IR spectrum of 5, two strong absorption bands at 1335 and
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1545 cm-1 are assignable to nitro group. Furthermore, the mass spectrum of 5 showed the molecular ion peak at m/z 292 (M+) corresponding to the molecular formula C16H12N4O2.
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Conversion of dye 4 to dye 3 was also examined. The color of blue solution of dye 4 in KOH/MeOH was smoothly changed to green which indicates the formation of 3 anion (Dye 3 was precipitated after neutralization the solution with dilute HCl). However, these evidences
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prove that dyes 3 and 4 are not well enough stable and they can convert to each other in appropriate conditions.
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Alkylation of active protons of dyes 3 and 4 prevents from tautomerization of these dyes. Compound 3 was methylated by dimethyl sulfate (DMS) in K2CO3 and MeCN to give new green dye 5-(methoxyimino)-1-methyl-1H-indazol-4(5H)-ylidene)-2 phenylacetonitrile (6) at rt (Scheme 4). New blue dye 2-(1-methyl-5-nitroso-1H-indazol-4-yl)-2-phenylpropanenitrile (7)
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was also obtained from the reaction of dye 4 with methyl iodide in potassium tert-butoxide and tert-butanol in good yield (Scheme 4). All the newly synthesized dyes have been characterized by elemental analysis and spectroscopic data. The spectral details of all these are given in
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experimental section.
3.2. Optical properties
The new dyes 4–7 were spectrally characterized by using a UV-vis spectrophotometer and the wavelength range of spectrophotometer was 200–800 nm. Fig. 1 shows the visible absorption spectrum of compounds 3 and 4–7 in dilute (2 × 10-6 M) methanol solution. Characteristics of absorption spectra for 3 and 4–7 in methanol are presented in Table 1. Values of extinction
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coefficient (ε) were calculated as the slope of the plot of absorbance vs concentration. Absorbance intensity and extinction coefficient (ε) in blue dye 4 were the biggest values. It should be emphasized that nitroso group is the strongest chromophore, being able to shift
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bathochromically absorption of given aromatic compound more than any other two-atom
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