Investigation of electrochemical, optical, and thermal properties via oligomerization of aminophenol monomer containing halogen and nitro groups using two distinct oxidants

Abstract

In this study, two different oligomers of 2-amino-4-chloro-5-nitrophenol (ACNP) with incorporated halogen atom and nitro groups were synthesized by oxidative oligomerization method using two different oxidants, namely H2O2 and ammonium persulfate (APS). Structural characterizations of the obtained products were elucidated by 1H NMR, 13C NMR, FT-IR, UV–Vis spectroscopy methods. The molecular masses of the oligomers were determined through the utilization of Gel Permeation Chromatography (GPC). The analysis revealed that the Mw values of the oligomers synthesized via the oxidative oligomerization method using H2O2 and APS, denoted as OACNP-1 and OACNP-2 were 4150 Da and 2800 Da, respectively. Using the UV–vis spectrophotometer, the optical band gaps were calculated as 2.64 eV, 1.95 eV and 2.14 eV for ACNP, OACNP-1 and OACNP-2, respectively. Thermal properties of the oligomers were investigated using Thermal Gravimetric Analysis-Differential Thermal Analysis (TGA-DTA) and Differential Scanning Calorimetry (DSC). The results demonstrated that OACNP-1 exhibited significantly higher thermal stability when compared to both the monomer and OACNP-2. In addition, Fluorescence Spectroscopic analysis of the oligomers revealed that OACNP-1 emitted blue light at 440 nm when excited with light of a wavelength of 370 nm, exhibiting fluorescent characteristics. Furthermore, the surface properties and morphologies of the oligomers were analyzed with the help of Scanning Electron Microscopy (SEM), revealing a flower-like structure for the oxidative oligomerization product, OACNP-1, in the presence of H2O2. In course of a change in the oxidant, the oligomer, OACNP-2, had rough and spongy surface morphology with some pores.