Elsevier

Materials Chemistry and Physics

Volume 222, 15 January 2019, Pages 37-44
Materials Chemistry and Physics

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

https://doi.org/10.1016/j.matchemphys.2018.09.080Get rights and content

Highlights

  • The novel oligo-pyrazole based polyamides are synthesized and to prepared their films.

  • Optic properties and surface morphologies of the prepared films were measured such as absorbance, transmittance and optical band gaps.

  • The structures of oligo-pyrazoles were confirmed by theoretical calculation and spectroscopic data.

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

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 o-phenylene-diamine. The structures of synthesized oligo-pyrazoles were characterized by 1H, 13C NMR, 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.

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], [2], [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], [5], [6], [7], [8]]. Furthermore, CPs led to the formation of a new technology both 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], [12], [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], [15], [16], [17]]. CPs possessed a wide range of optical and physicochemical properties [[18], [19], [20]]. Therefore, π-conjugated structures in the polymers have been significant target molecules for material chemists. Polypyrazoles and oligo-pyrazoles are important classes of the heterocyclic polymers. They have been known to display some important properties such as high thermal stability, mechanical, optics and optoelectronic etc [[21], [22], [23], [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 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. Hence, in previous work can be guidance in the pyrazole chemistry field particularly pyrazole-3-carboxylic acid derivatives for many researchers.

Aim of this study is to synthesize two novel conjugated oligo-pyrazoles and to investigate 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.

Section snippets

Materials and equipment

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 13C (100 MHz) NMR spectra were recorded on a Bruker DRX-400 high performance digital FT-NMR spectrometer. NMR spectra were obtained in solutions of DMSO‑d6. Molecular weights and PDI of the oligo-pyrazoles were determined by gel permeation chromatography (GPC) using Agilent 1100

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 chemo-selectivity [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 spectroscopic methods which are

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 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

Acknowledgment

The authors are thankful the partially support of Muş 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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