Synthesis, characterization and photovoltaic studies of oligo(acriflavine) via chemical oxidative polymerization

Abstract

The present work reports a simple and inexpensive way for the synthesis of a novel water-soluble conjugated oligo(acriflavine) (OAC). Oligo(acriflavine) was synthesized via chemical oxidative polycondensation by H₂O₂ (30%) as the oxidant at an optimum reaction temperature of 110 °C without use of an additional external template. The chemical structure of the synthesized compound was confirmed by FT-IR, UV-Vis, ¹H-NMR and ¹³C-NMR techniques. Further characterization was employed using, photophysical, electrochemical, photovoltaic thermogravimetric-differential thermal analysis (TG-DTA), fluorescence (PL), cyclic voltammetry (CV) and differential scanning calorimetry (DSC) measurements. The number average molecular weight of the oligomer was found to be 4950 Da with a polydispersity index of 1.18. Photoluminescence (PL) properties of the synthesized materials were determined in solution form. The solvent effect on the optical properties of OAC was studied in selected solvents. The spectral analysis displayed a bicolor emission behavior when OAC solution was irradiated at different wavelengths. The HOMO–LUMO energy levels and electrochemical (E′_g) band gap values of OAC were determined by CV measurement. Optical and electrochemical band gaps of OAC with more conjugated structure were lower than for AC. XRD analysis signified that the oligomer was in a semi-crystalline form. To further study the morphologic properties of the OAC, Scanning Electron Microscopy (SEM) images were illustrated at different amplifications. It was demonstrated that the structure of OAC was essentially a ladder oligomer with phenazine rings. The best performing photovoltaic cell, based on OAC reached a J_sc of 0.14 mA cm⁻², a V_oc of 0.37 V, and a FF of 0.50, giving a power conversion efficiency (% η) of 0.027% under AM 1.5 irradiation (100 mW cm⁻²).