Synthesis and characterization of substituted poly(naphthalene)s with imine bonding containing thiophene unit

Abstract

In this study, 5-(4H-dithieno[3,2-b:2′,3′-d]pyrrol-4-yl)naphthalen-1-amine was synthesized from the required reaction conditions of 3,3′-dibromo-2,2′-bithiophene with 1,5-diamine naphthalene. Then, Schiff base monomers were synthesized from the condensation reactions of 5-(4H-dithieno[3,2-b:2′,3′-d]pyrrol-4-yl)naphthalen-1-amine with mono aldehydes such as 2-hydroxybenzaldehyde, 4-hydroxybenzaldehyde and isovaniline. The Schiff base monomers were polymerized via oxidative polycondensation in 0.1 M KOH aqueous solution at 90 °C by 10–15% NaOCl oxidant. The structures of synthesized compounds were carried out by FT-IR, UV–Vis, 1H NMR, 13C NMR techniques. Further characterization was implemented by cyclic voltammetry (CV) electrochemical properties, fluorescence (FL) measurements, electrical properties, thermogravimetric-differential thermal analysis (TG-DTA) and differential scanning calorimetry (DSC) measurements. Depending on structural changes of synthesized polymers, differences were observed for the optical, electrochemical, thermal and physical properties. The optical and electrochemical band gaps, conductivity and fluorescence properties of P1 were found to be better than other polymers. The fluorescence intensity of P1 in two different wavelengths was found to be 632 a.u. and 1000 a.u. The optical (Eg) and electrochemical band gap values (E'g) of P1 were found to be 2.34 and 2.25 eV, respectively. This low band gap values have demonstrated to be a good conjugation in the structure. According to TG measurements, Ton temperature of P1, P2 and P3 were found to be 227, 293 and 306 °C, respectively. The weight average molecular weight (Mw) of P1, P2 and P3 were calculated to be 39500, 40150 and 44300 Da, respectively.