Synthesis, characterization and electrochemical properties of poly(phenoxy-imine)s containing carbazole unit

Int J Ind Chem DOI 10.1007/s40090-017-0112-5 RESEARCH Synthesis, characterization and electrochemical properties of poly (phenoxy-imine)s containing carbazole unit İsmet Kaya1 · Sebra Çöpür1 · Hatice Karaer1,2 Received: 29 June 2016 / Accepted: 11 January 2017 © The Author(s) 2017. This article is published with open access at Springerlink.com Abstract Several new Schiff base polymers were synthesized via oxidative polymerization method in an aqueous alkaline medium in the presence of NaOCl as an oxidant and were confirmed by FT-IR, 1H-NMR, 13C-NMR and UV–Vis spectroscopic techniques. Furthermore, cyclic voltammetry measurements were carried out and the HOMO–LUMO energy levels and electrochemical band gaps (Eg′) were calculated. Additionally, the optical band gaps (Eg) were determined using their UV–Vis spectra of the materials. The morphologic properties of the polymers were investigated by scanning electron microscopy. In addition, the number average molecular weight (Mn), weight average molecular weight (Mw) and polydispersity index values of the polymers were determined by gel permeation chromatography technique. Electrical conductivity measurements of the doped (with iodine) and undoped polymer related to doping time were carried out by four-point probe technique using a Keithley 2400 electrometer. Their thermal behaviors were determined by TG–DTA and DSC measurements. The synthesized compounds were soluble in common solvents such as DMF, THF and DMSO. Photoluminescence properties of the polymers were determined in different concentrations of DMF solvent. & İsmet Kaya 1 Polymer Synthesis and Analysis Laboratory, Department of Chemistry, Çanakkale Onsekiz Mart University, 17020 Çanakkale, Turkey 2 Department of Chemistry, Faculty of Sciences, Dicle University, 21280 Diyarbakır, Turkey Keywords Carbazole · Fluorescence · Thermal analysis · Poly(phenoxy-imine) · Band gaps Introduction Poly(imine)s, known as Schiff base polymers or poly (azomethine)s or also named polyazines (when hydrazine is used as diamine compound) [1] which are of great interest to researchers because of to their potential applications and advantageous properties. Recently, polyazomethines have attracted much attention of both industries and academia and they have been widely investigated for their electrochemical properties, thermal stability, fluorescence, intrinsic conductivity [2]. Polyimines conjugated polymers have claimed the attention of researchers because of their potentially advantageous electronic applications, such as their electrical properties and environmentally stability, with acceptable mechanical strength [3]. Polyazomethines are conducting polymers [4] that usually show an optical absorption band in the visible region owing to their extended delocalization of the π electrons along the polymer backbone. Upon doping with suitable dopants, charge carriers, namely bipolaron and polaron, are formed in the conjugated backbone. This class of polymers was primarily found to be electroactive as well as semiconductive materials [5, 6], and their conductivity could be increased by doping with a dopant like iodine [2]. Furthermore, Schiff base polymers have been become increasingly interesting in the field of optical materials since they possess great potential for device applications like light-emitting diodes, photovoltaic cells and thin film transistors [7]. Poly(azomethine)s including conjugated bonding and active hydroxyl group have been studied for more than 123 Int J Ind Chem 60 years, and used in several fields [8]. The oxidative polymerization method is simply the reaction of compounds including –OH groups and active functional groups (–CHO, –NH2, –COOH) in their structure with the oxidants like air oxygen NaOCl, H2O2 an in the aqueous alkaline medium [9]. Carbazole-containing polymers are of great interest owing to their several potential for applications in organic electronics, such as organic solar cells, organic field effect transistors (OFET) and organic light-emitting devices (OLED), etc. [10]. In this study, new Schiff bases were synthesized by condensation reaction of 4-diethylaminosalicylaldehyde, 3,4-dihydroxybenzaldehyde and 2,4-dihydroxybenzaldehyde compounds with 3-amino-9-ethyl-carbazole. Then, these products were polymerized via oxidative polycondensation method in an aqueous alkaline medium in the presence of NaOCl as an oxidant. The structures of all compounds were confirmed by FT-IR, UV–Vis, 1H-NMR Scheme 1 Syntheses of Schiff bases and their polymers 123 and 13C-NMR measurements. Thermal stabilities of all compounds were determined by TG–DTA and DSC measurements. Also, the conductivity and photoluminescence (PL) properties of polymers were determined from fourpoint probe technique and spectrofluorophotometer measurements, respectively. Experimental Materials 3-Amino-9-ethyl-carbazole, ethyl alcohol, ethyl acetate, chloroform, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile and sodium hypochlorite (NaOCl, 37%) were supplied from Merck Chemical Co. (Germany). 4-Diethylamino salicylaldehyde (Alfa Aesar), 3,4-dihydroxybenzaldehyde (Fluka) and 2,4dihydroxybenzaldehyde were supplied from Acros. Int J Ind Chem Synthesis of the monomers (DEACIMP, ACIMB and ACIBM) The synthesis of 5-(diethylamino)-2-[(3-amino-9-ethylcarbazole) imino methyl] phenol (DEACIMP) was synthesized according to the literature [11] (Scheme 1) as follows: 4-diethylamino salicylaldehyde (1.77 g) and 3-amino-9-ethyl-carbazole (1.95 g) were dissolved in 20 mL absolute ethanol in two separate beakers, which were then mixed. This mixture was refluxed for 5 h in a two-necked flask and cooled to room temperature. The precipitate formed was filtered, washed with ethanol and then dried under reduced pressure. The same procedure was used to obtain 4-[(3-amino-9-ethyl-carbazole) imino methyl] benzene-1,2-diol (ACIMB) and 4-[(3-amino-9ethyl-carbazolyl) benzene imine methyl]-1,3-diol (ACIBM) the 3,4-dihydroxybenzaldehyde (1.38 g), 3-amino-9-ethyl-carbazole (1.95 g) and 2,4-dihydroxybenzaldehyde (1.38 g), 3-amino-9-ethyl-carbazole (1.95 g) were used for synthesis the ACIMB and ACIBM, respectively. The yields of DEACIMP, ACIMB and ACIBM compounds were found to be 80, 85, 89, respectively. Characterization techniques A PerkinElmer spectrum one FT-IR system was used to determine the chemical structure of the monomers and polymers. Measurements were performed in solid powder form at room temperature using universal ATR sampling accessory within the wavelengths of 4000–650 cm−1. UV–Vis spectroscopy, was used to study the electronic transition in the General synthesis procedure of P-DEACIMP, P-ACIMB and P-ACIBM polymers P-DEACIMP, P-ACIMB and P-ACIBM were synthesized through the oxidative polycondensation of DEACIMP, ACIMB and ACIBM with aqueous solution of NaOCl (10%). P-DEACIMP was synthesized through oxidative polycondensation of 5-(diethylamino)-2-[(3amin (...truncated)