A study on synthesis, optical properties and surface morphological of novel conjugated oligo-pyrazole films

Accepted Manuscript A study on synthesis, optical properties and surface morphological of novel conjugated oligo-pyrazole films Adnan Cetin, Adem Korkmaz, Erman Erdoğan, Arif Kösemen PII:

S0254-0584(18)30840-X

DOI:

10.1016/j.matchemphys.2018.09.080

Reference:

MAC 21009

To appear in:

Materials Chemistry and Physics

Received Date: 10 May 2018 Revised Date:

26 September 2018

Accepted Date: 30 September 2018

Please cite this article as: A. Cetin, A. Korkmaz, E. Erdoğan, A. Kösemen, A study on synthesis, optical properties and surface morphological of novel conjugated oligo-pyrazole films, Materials Chemistry and Physics (2018), doi: https://doi.org/10.1016/j.matchemphys.2018.09.080. 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.

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A study on synthesis, optical properties and surface morphological of novel conjugated oligo-pyrazole films

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Muş Alparslan University, Faculty of Education, Department of Sciences, Muş, Turkey b

Muş Alparslan University, School of Health, Muş, Turkey

Muş Alparslan University, Faculty of Art and Sciences, Department of Physics, Muş, Turkey

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c

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Adnan Cetina*, Adem Korkmazb, Erman Erdoğanc, Arif Kösemenc

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*Corresponding author: [email protected], +904362130013-3671

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ABSTRACT: The two novel pyrazole based organic semiconductor 2a, 2b were synthesized from reactions of 1H-pyrazole-3,4-dicarbonyl dichloride 1c and p-phenylene-diamine or ophenylene-diamine. The structures of synthesized oligo-pyrazoles were characterized by 1H, 13CNMR, FT-IR, Gel Permission Chromatography (GPC). The novel oligo-pyrazole films were prepared from synthesized 2a, 2b and their thicknesses were found to be 84 and 220 µm. The optical properties of films such as absorbance, transmittance and band gap (Eg) were determined by UV-vis spectroscopy. Two dimensional and three dimensional surface images of films produced on glass were obtained with Atomic Force Microscope (AFM). In the AFM results, the average roughness and the average surface roughness values were obtained as 40.44, 3.15 nm and 55.14, 7.91 nm for oligo-pyrazoles (2a) and (2b). Also, the skewness values and kurtosis values were obtained as 5.04, 131.73 and 0.75, -8.49 for oligo-pyrazoles (2a) and (2b), respectively. Furthermore, the structures of the oligo-pyrazoles in the lowest energies were optimized by means of DFT calculation and their HOMO-LUMO orbitals were plotted. Keywords: Absorbance, Conjugated Polymer, Pyrazole, Organic semi-conductor, Optical band

1.

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gap

Introduction

The conjugated polymers (CPs) are important target molecules in polymer chemistry and material engineering due to important properties such as optic and optoelectronic [1-3]. So, optical and electronic properties to CPs had brought a different dimension to the industrial applications particularly solar cells, charge storage devices, biosensors, electrochromic panels and photovoltaic panels [4-8]. Furthermore, CPs led to the formation of a new technology both 1

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electronic and optical properties presence in one material such as diodes, transistors, solar cells, organic light-emitting, electrochromic and sensor devices [9, 10]. CPs are a popular topic for design of new materials due to various industrial applications such as organic solar cells, organic field effect transistors and organic light emitting diodes [11-

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13]. Also, CPs have increased the importance of the projects in this area so that the designed materials in that area have scaffold for organic and polymers chemists. CPs have grown widespread attention in chemistry, agricultural, textile and electronic industries [14-17]. CPs possessed a wide range of optical and physicochemical properties [18-20]. Therefore, π-

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conjugated structures in the polymers have been significant target molecules for material chemists. Polypyrazoles and oligo-pyrazoles are important classes of the heterocyclic polymers.

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They have been known to display some important properties such as high thermal stability, mechanical, optics and optoelectronic etc [21-24]. Therefore, pyrazole based structures were incorporated into the backbone of a number of polymers [25, 26].

In addition, the heterocyclic compounds having pyrazole structure are scaffold molecules due to specific properties such as biologic, medicine, agriculture etc. [27, 28]. Therefore, the pyrazole derivatives and their biological activities have been reported in the literature for last

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decade. First time, the pyrazole based oligomers were synthesized from starting material pyrazole-3-carboxylic acid and optical properties of their films were investigated by our research group [22, 29]. The obtained films from prepared pyrazole molecules were determined their optic parameters. It can be said that lead different dimensions for pyrazole-3-carboxylic derivatives.

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Hence, in previous work can be guidance in the pyrazole chemistry field particularly pyrazole-3carboxylic acid derivatives for many researchers. Aim of this study is to synthesize two novel conjugated oligo-pyrazoles and to investigate

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the optoelectronic properties of their films. The structures of the synthesized oligo-pyrazoles were confirmed by spectroscopic analysis and their molecular weights were determined by GPC. The optical parameters of the films were measured. 2D and 3D AFM images of the film samples were taken to determine the morphological surface. 2.

Experimental methods

2.1. Materials and equipment

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All reagents and solvents were purchased from Merck, Sigma and Aldrich companies. These materials were used without purification. Infrared spectra were recorded on a Shimadzu IR-470 spectrophotometer. 1H (400 MHz) and

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C (100 MHz) NMR spectra were recorded on a

Bruker DRX-400 high performance digital FT-NMR spectrometer. NMR spectra were obtained

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in solutions of DMSO-d6. Molecular weights and PDI of the oligo-pyrazoles were determined by gel permeation chromatography (GPC) using Agilent 1100 Series, equipped with refractive index detector. The optical measurements of oligo-pyrazole films were carried out with a Shimadzu model UV-1800 Spectrophotometer in the wavelength range of 1100-190 nm at room

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temperature. An Ambios Q-Scope AFM device was used to study the surface structures of the films. Both ethyl 4-(chlorocarbonyl)-1,5-diphenyl-1H-pyrazole-3-carboxylate (1a) (mp 173 oC)

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and its derivatives 1,5-diphenyl-1H-pyrazole-3,4-dicarboxylic acid (1b) (mp 224-225 oC) and 1,5-diphenyl-1H-pyrazole-3,4-dicarbonyl choloride (1c) (mp 86-89

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C) as our starting

compounds were synthesized via related literature [30, 31]

2.2. General procedure for synthesis of oligo-pyrazoles (2a, 2b)

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The pyrazole-3,4-dicarbonyl chloride 1c (0.17 g, 0.5 mmol) was dissolved in anhydrous tetrahydrofuran (10 mL). Substituted phenylene diamine derivatives (p-phenylene-diamine and ophenylene-diamine) (0.056 g, 0.5 mmol) were added to the reaction pot and the mixture was refluxed for 24 hours under an atmosphere of argon gas with low pressure. They were cooled to

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room temperature. The solvent was evaporated. The precipitated products were washed with diethyl ether. Then the products were filtered and dried.

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2.3. Synthesis of olygo(p-phenylene-1-phenyl)-5-phenyl-1H-pyrazole-3,4-dicarboxyamide (2a) 2a was synthesized according to the general procedure. Yield: 86%. IR (ν, cm-1): 3369 (N-H, amide), 3050, 2928 (C-H, aromatic), 1651 (C=O, amide), 1595-1568 (C=N), 1511-1418 (C=C), 1310 (C-N). 1H-NMR (400 MHz, DMSO-d6) δ (ppm): 9.5 (-NH, amide), 8.0-7.5 (m, Ar-H), 5.5 (NH, aromatic).

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C-NMR (100 MHz, DMSO-d6) δ (ppm): 172.4 and 169.6 (-C=O), 143.5 (C3),

140.7 (C5), 138.7, 136.9, 135.1, 131.1, 131.0, 130.3, 130.0, 129.6, 129.6, 129.3, 128.4, 128.2,

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126.6, 124.4, 123.7, 120.6, 110.8 (C4). Mn=1197 g/mol, Mw=1582 g/mol, (polydispersity index, PDI, 1.321).

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2.4. Synthesis of olygo(o-phenylene-1-phenyl)-5-phenyl-1H-pyrazole-3,4-dicarboxyamide (2b) 2b was synthesized according to the general procedure. Yield: 81%. IR (ν, cm-1): 3290, 3230 (N-H, amide), 3060, 2926 (C-H, aromatic), 1657 (C=O, amide), 1594-1510 (C=N), 1496-1446 (C=C), 1367 C-N). 1H-NMR (400 MHz, DMSO-d6) δ (ppm): 10.2 (-NH, amide), 7.9-6.3 (m, Ar13

C-NMR (100 MHz, DMSO-d6) δ (ppm): 169.3 and 166.5 (-C=O),

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H), 5.4 (-NH, aromatic).

150.5 (C3), 144.9 (C5), 139.0, 134.8, 132.0, 130.7, 129.6, 128.6, 128.2, 125.1, 121.2, 119.8,

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114.3, 111.2 (C4’). Mn=1491 g/mol, Mw=3093 g/mol, (polydispersity index, PDI, 2.077). 2.5. Preparation of films the synthesized oligo-pyrazoles (2a, 2b)

At first, the oligo-pyrazoles (2a, 2b) were added to 1 mL DMF. The solutions of the 2a, 2b were stirred in DMF at room temperature for 1 hour. The oligo-pyrazoles, which were insoluble

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in the solvent, were removed to filtrating with filter paper. The glass surface was cleaned with a piranha solution (sulfuric acid and hydrogen peroxide). Then, it was rinsed with water. The solutions of the 2a and 2b were added dropwise to coat the film on the glass and left to dry automatically. The films of the 2a, 2b were obtained by this method [29]. Thicknesses of films

Results and discussion

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were measured with the micrometer (sensitivity is 0.001 mm).

3.1. Synthesis and characterization

Polypyrazoles and oligopyrazoles are the most extensively studied method in polymer chemistry and organic chemistry because of its reliability, easy accessibility and chemoselectivity [32, 33]. For this purpose, firstly 1a was synthesized according to literature [30] and 1b was synthesized from the basic hydrolysis of 1a. The starting material 1c was prepared by heating 1b and excess thionyl chloride. All the synthesized compounds (1a-c) were confirmed by 4

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spectroscopic methods which are agreement with our previous findings [34]. The synthetic methods were used for the syntheses of oligo-pyrazoles. The cycloaddition reaction is used one of the most for the preparation of oligo-pyrazoles. It was applied one step procedure for the preparation of oligo-pyrazoles in Scheme1. The olygo(p-phenylene-1-phenyl)-5-phenyl-1H-

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pyrazole-3,4-dicarboxyamide (2a) and olygo(o-phenylene-1-phenyl)-5-phenyl-1H-pyrazole-3,4dicarboxyamide (2b) were synthesized via the reaction of the starting material 1c and pphenylene-diamine with o-phenylene-diamine to about one day at reflux in tetrahydrofuran as

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solvent under an atmosphere of argon gas with low pressure (Scheme 1). Scheme1. Synthesis of the oligo-pyrazoles

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The number of average molecular weights (Mn), average molecular weights (Mw) and polydispersity indexes (PDI) of the synthesized oligo-pyrazoles were determined by GPC using poly(methyl methacrylate). Mn, Mw and PDI values of the oligo-pyrazoles were observed as 1197, 1582, 1.321 g/mol-1 for 2a and 1491, 3093, 2.077 g/mol-1 for 2b, respectively. According to GPC spectra, the synthesized oligo-pyrazoles should be trimer structure for 2a and tetramer structure for 2b. So, the synthesized oligo-pyrazole 2a possessed three identical N-terminal units

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on both sides. The synthesized oligo-pyrazole 2b also had four identical N-terminal units in the olygomer structure. Besides, the synthesized oligo-pyrazoles were not symmetric in terms of unsymmetrical starting material (monomer).

The structures of the oligo-pyrazoles were also confirmed by IR, 1H NMR and

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C NMR

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spectra (see Experimental). The FTIR bands at 3369, 3290, 3230 cm observed to the -NH amide groups for 2a and 2b, respectively. The signals of the oligo-pyrazoles were seen at 1651 and 1657 cm-1 for 2a and 2b as peaks due to the amide carbonyl structures. The bands at 3050, 2928

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and 3060, 2926 cm-1 observed due to the aromatic C-H stretching vibrations for 2a and 2b, respectively. In the case of the synthesized oligo-pyrazoles, the correct structures were established by 1H NMR and

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C NMR spectroscopy in which characteristic the presence of

protons of C=NH peaks were observed at δ 5.5 ppm and the protons of the NH peaks for 2a and 2b were observed at δ 9.5 and 10.2 ppm and also appeared the resonance peaks as multiplets in the region 6.3 to 8.0 ppm due to the aromatic protons of the 2a and 2b structures. The 13C-NMR spectrum revealed the signals carbonyl of amide groups in the region 172.4, 169.6, 169.3 and 166.5 ppm and the signals of (C3), (C5) and (C4) at the pyrazole ring were also observed at 5

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143.5, 150.5, 140.7, 144.9 and 108.4, 111.2 ppm for 2a and 2b, respectively. Thermal degradation behaviors of olygo-pyrazoles were determined by using thermogravimetric analysis (Fig.1). These processes were obtained in the temperature range 25-1000°C with a heating rate of 10 °C / min under nitrogen atmosphere. The results were summarized in Table 1. The weight

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losses % at 400, 500, 600, 700 and 800 oC of olygo-pyrazoles were found to 12, 40, 66, 78 and 92 for olygo-pyrazole 2a and 8, 26, 54, 70 and 92 for olygo-pyrazole 2b, respectively. The results showed that olygo-pyrazole 2b had higher residue than olygo-pyrazole 2a due to tetramer

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Fig.1. TGA curves of olygo-pyrazoles

Table 1. Thermogravimetric analysis data weights loss % for oligo-pyrazoles

3.2. Theoretical Calculations

The initial geometries for the target oligo-pyrazoles were constructed with GaussView 5.0

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package [36] and their subsequent optimization studies were performed using the AM1 method as implemented in Gaussian 09W software [37]. The oligo-pyrazole 2a (trimer) and oligo-pyrazole 2b (tetramer) in their lowest energies are depicted in Figure 2.

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Fig.2. Theoretically optimized structures of oligo-pyrazoles 2a (left) and 2b (right)

As could be seen from Fig.2, the optimized geometry of 2a has a triangular cage-like

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compact structure whereas the 2b has a V-shape orientation. This valuable geometrical difference could be due to the ortho- (2b) or para- (2a) substitution effects. Especially for the case of 2b, the influence of the phenyl group’s sterically hindrance on the pyrazole subunits end up by the angular transposition of the oligomer units in order to reach to a more stable geometry. The para disubstitution on 2a has important domination to stabilize the structure with the aid of the intramolecular non-covalent bonding (such as hydrogen bonding). In other words, for both of the oligomers, the intramolecular non-covalent bonding decreased the energies and resulting in packed-type geometry. The energy levels of the lowest unoccupied molecular orbital (LUMO) 6

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and the highest occupied molecular orbital (HOMO) are important physicochemical parameters. The HOMO and LUMO orbitals of oligo-pyrazoles were calculated, and the corresponding counterplots were given in Figure 3. The HOMO orbitals of oligo-pyrazole 2a were localized primarily on one of pyrazole skeleton and diaminobenzene rings, phenyl groups and carbonyl

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groups, whereas the LUMO orbitals of oligo-pyrazole 2a were localized only on one of the diaminobenzene rings and its amide group (Fig.3) due to intramolecular charge transfer. The HOMO orbital of 2b was centralized on the diaminobenzene subunit, and its LUMO orbital was

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detected along the central pyrazole subunit including the two phenyl rings.

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Fig.3. HOMO and LUMO orbitals for oligo-pyrazoles

3.3. The optical properties of the oligo-pyrazole films

Optical properties of the oligomer films were determined by UV-vis spectroscopy [29]. The novel pyrazole based oligomer structures and their films can draw attention due to optical properties and electronical applications. Moreover, substituted pyrazoles having π-conjugated

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structures should be significant candidate materials due to π–π intermolecular interactions [38]. Hence, in the present work, the films of newly synthesized oligo-pyrazoles were carried out to determine their optical properties such as absorbance (A) and transmittance (T) values. A plot absorbance versus wavelength was plotted for 84 µm coated oligo-pyrazole (2a) and 220 µm

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coated oligo-pyrazole (2b) films in Fig. 4.

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Fig.4. The absorbance graph as function of wavelength for oligo-pyrazole films

As seen in Figure 4, it was observed that 84 µm coated oligo-pyrazole (2a) absorbed less than 220 µm coated oligo-pyrazole (2b). When the wavelength of the oligo-pyrazole films decreased, the absorbance values increased. In particular, there is a standard increase in the range of 400-700 nm for oligo-pyrazole (2a) film. It stayed sensibly fixed for a short time. Eventually, it started to grow again. It was observed that the absorbance curve of the oligo-pyrazole (2b) film was different from that of the oligo-pyrazole (2a) film. This difference was clearly observed in

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the range of 450-550 nm. Here, a sharp increasing in the oligo-pyrazole (2b) film was observed. However, the oligo-pyrazole (2a) film showed a standard increasing in this range. In this case, it can be concluded that the absorbent region of oligo-pyrazole (2a) and oligo-pyrazole (2b) is closer to the boundaries of near ultraviolet and visible region [39]. The transmittance graph for 84

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µm coated oligo-pyrazole (2a) and 220 µm coated oligo-pyrazole (2b) films was observed as in Fig.5. Transmittance values of oligo-pyrazoles films were observed to be very low. As can be seen in the graph in Fig. 5, the transmittance value of oligo-pyrazole (2a) was observed to be in the range of 0-24%. It is clear that the transmittance value of oligo-pyrazole (2a) is very low. The

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transmittance value for oligo-pyrazole (2b) film is lower than oligo-pyrazole (2a) film. It can be

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said that the amount of light passing through the oligo-pyrazole (2b) film is very small.

Fig.5. The transmittance graph as function of wavelength for oligo-pyrazoles films

The pyrazole based oligomer films (2a, 2b) having low band gap values might be desired materials for optoelectronic and solar cell devices due to low weight, easy process ability and low-cost performance [40]. Also, one of the most important parameters for optical properties in

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film coating is band gap energy (Eg, eV) value. Therefore, to find the direct band gap of the oligopyrazoles (2a, 2b) were plotted the photon energy versus (α.hν)2 by using Tauc equation (Fig. 6)

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[41, 20].

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Fig.6. The graph of (αhν)2 with photon energy for the oligo-pyrazole films

As shown in Fig. 6, the Eg values of the films for 84 µm coated oligo-pyrazole (2a) and 220 µm coated oligo-pyrazole (2b) were found to be 1.523 and 2.079 eV, respectively. It was observed that the Eg values of the newly synthesized oligo-pyrazoles (2a, 2b) are very low. Band gap of oligo-pyrazole (2a) film was observed to be lower than that of oligo-pyrazole (2b) film. This is thought to be due to different structures of the used p-phenylenediamine and ophenylenediamine substrates. When p-phenylenediamine was used, the resulting oligo-pyrazole (2a) molecule had a linear structure. Conversely when o-phenylenediamine was used, the oligopyrazole structures moved away from the linear dimension. Furthermore, since the active ends in 8

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o-phenylenediamine were in close proximity to each other at 1,2 positions, the resulting obtained structure had also formed a steric hindrance. In this case, it is clear that when ophenylenediamine was used, it had made a negative contribution to the conjugation of the oligopyrazole (2b) structure. To increase conjugation, the structure must be linear and the steric

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hindrance minimal so that the overlapping of the p orbitals can be so easy. In these circumstances, the conjugation in structure increases even more [42-44]. It could be concluded that the synthesized oligo-pyrazole (2a) was to be easier to conjugate than synthesized oligopyrazole (2b). It was confirmed that the Eg value of oligo-pyrazole (2a) was lower than that of

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oligo-pyrazole (2b). If the oligo- pyrazole (2a) and oligo-pyrazole (2b) had the same film thickness, the oligo-pyrazole (2a) band gap value would be lower than the oligo-pyrazole (2b)

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due to its structure. Normally, as the film thickness increased in organic films, the value of Eg decreased [45]. In this study, it was observed that the band gap value was still low, although oligo-pyrazole (2b) coated film thickness (220 µm) was almost 3 times greater than the oligomerpyrazole (2a) coated film thickness (82 µm). The foreseen scientific data was confirmed as a result of the experimental studies carried out.

To find the value of the indirect optical band gap (Egid) was plotted the photon energy versus

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(α.hν)1/2 (Fig. 7). The Egid values of 84 µm coated oligo-pyrazole (2a) and 220 µm coated oligopyrazole (2b) films were found to be 0.534 and 1.156 eV, respectively. Direct band gap (Egd) values were lower than indirect band gap (Egid) values (see Table 2). It was also seen that the direct transition was sharper than the indirect transition (Fig. 6 and Fig. 7). In this case, the direct

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transition was more appropriate than the indirect transition. It was known that the direct band gap semiconductors absorbed more light than the indirect band dap semiconductors [46]. Thus, the having semiconductors synthesized 2a and 2b absorbed the light needed for solar energy more

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effectively. 2a and 2b oligo-pyrazoles may be candidate for optical applications. Fig.7. The graph of (αhν)1/2 with photon energy for oligo-pyrazoles films

Table 2. Direct, indirect, forbidden indirect band gap values of oligo-pyrazoles films

A plot of E (eV) versus (αhν)

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was plotted for oligo-pyrazoles (2a, 2b) films in Fig. 8.

Here, the relevant value of forbidden indirect (Egfid) values were obtained 1.112 and 1.677 eV for 84 µm coated oligo-pyrazole (2a) and 220 µm coated oligo-pyrazole (2b) films, respectively. 9

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Fig. 8. The graph of (αhν)1/2 with photon energy for oligo-pyrazoles films

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3.4. The surface morphology of the oligo-pyrazole films

The morphological characteristics of a section on the oligo-pyrazoles (2a, 2b) were examined. AFM was used to investigate surface morphology, surface roughness and height distribution histogram of the olygo-pyrazoles. Some spatial features of surface topology were

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determined statistically and they were analyzed by histogram analysis. Two- and threedimensional images were scanned at a scanning speed of 9 µm x 9 µm at a scanning speed of 0.7

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Hz using the surface morphologies of the olygo-pyrazole films deposited on the glass substrate via the AFM device in non-contact form. Fig.9a,b showed best scanned area of two-dimensional and three-dimensional AFM images of oligo-pyrazoles on glass substrate, respectively.

Fig.9. The 2D and 3D images of the oligo-pyrazole films 2a and 2b

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When looking at AFM images, black regions appeared in a few places and relatively yellow regions appeared in a large places. While the black regions represented the valley in the surface, the white regions represented the peaks. The lowest point in the image was determined as the zero height and all remaining pixels were evaluated with respect to this zero point. The

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average height of the examined specimen was determined by AFM software by taking the average of all pixel counts. The average roughness values which expressed average deviation values from the plane of the main surface were found to be 40.44 and 3.15 nm for oligo-pyrazoles

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(2a) and (2b). Also, the mean square root surface roughness value with the determination of the square root deviation values of the mean roughness values were found to be 55.14 and 7.91 nm for oligo-pyrazoles (2a) and (2b) at whole films. Surface histogram analysis of surface distribution was used to determine skewness and kurtosis values. The surface was evaluated with a skewness value which indicated a symmetrical distribution or an asymmetric distribution. Skewness value of the oligo-pyrazole (2a) film was 0.75. Obtaining as a positive skewness value means that the peaks on the film surface were more dominant than the valleys in the surface distribution [47]. Skewness value of the oligo-pyrazole (2b) film was -8.49. Negative skewness 10

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value was shown that the valleys on the film surface were more dominant than the peaks. In addition the surface had more planar and hollow structure. The spiky structures or planarity of the surface distribution of the dimensions was evaluated by kurtosis value [48]. Kurtosis values of the oligo-pyrazoles (2a, 2b) films were 5.04 and 131.73, respectively. Moreover, if kurtosis value

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has greater than 3, it means that had high peaks and low valleys with a spiky surface. Height distribution graphs of the oligo-pyrazoles (2a, 2b) films were attained by aid of the AFM tool and were also shown in Fig. 10a,b. Height distribution plot was associated with the homogeneous grain distribution on the surfaces. According to the graphs, the film on glass substrate exhibited a

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perfect Gauss curve.

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Fig.10. Gauss curves of the height distribution graph of the oligo-pyrazole films 2a and 2b

Conclusions

The novel two conjugated oligomers having pyrazole structures were synthesized and their films were prepared. The band gap values of 84 µm coated oligo-pyrazole (2a) and 220 µm

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coated oligo-pyrazole (2b) films were found as 1.523 and 2.079 eV, respectively. The band gap value of oligo-pyrazole (2a) film was lower than the band gap value of the oligo-pyrazole (2b) film. This is thought to be due to the fact that oligo-pyrazole (2a) has better conjugation than oligo-pyrazole (2b). In addition, it can be said that the desired optical properties can be achieved

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by adjusting the oligo-pyrazole structure. In the results of AFM, surface of oligo-pyrazole film (2b) had extremely low roughness values in films. Especially for oligo-pyrazole (2b) film, the

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negative skewness value indicated that the pits on the surface were more prominent than the valleys. The oligo-pyrazole films had high kurtosis values. These films might be suitable structures for friction applications in engineering area. Furthermore, the olygo-pyrazole films might be suitable for optoelectronic applications due to exhibiting good surface morphology and having low band gaps.

Acknowledgment

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The authors are thankful the partially support of Mus Alparslan University (BAYPUAM) (Grant no: MSÜ14-EMF-G05) and the authors also thank Research Assistant Gülbin Kurtay in Ankara University who helped theoretical calculation works.

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Appendix A. Supplementary data

Supplementary data associated with this article can be found, in the online version, at …

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Table 1. Thermogravimetric analysis data weights loss % for oligo-pyrazoles 400oC

500oC

600oC

2a 2b

12 8

40 26

66 54

700oC

800oC

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78 70

92 92

Film thickness (µm)

Egd (eV)

Egid (eV)

Egfid (eV)

2a

84

1.523

0.534

1,112

2b

220

2.079

1.156

1,677

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ACCEPTED MANUSCRIPT HIGHLIGHTS The novel different oligo-pyrazole based polyamides are synthesized and to prepared their thin films. transmittance and optical band gaps.

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Optic properties of the prepared films were measured such as absorbance, The structures of oligo-pyrazoles were confirmed by theoretical calculation and spectroscopic data.

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This synthesized polyamides may be used for applications in optoelectronic devices.