Salient Optical and Electrical Properties of Poly(vinyl alcohol) Films Inculcated by Two Copper(II) Complexes

Abstract

In-depth experimental and theoretical investigations on tailoring of optical and electrical properties in poly(vinyl alcohol) (PVA) composite films through the incorporation of copper(II) complexes have been carried out. Purposely, single crystals of two dinuclear copper(II) complexes, [Cu₂(H₂tea)₂(4-chloro-2-nitrobenzoate)₂] (1) and [Cu₂(H₂tea)₂(2-chloro-5-nitrobenzoate)₂] (2), were prepared and subjected to X-ray diffraction. The electronic structures of complexes 1 and 2 were analyzed through CASTEP-based density functional theory calculations, revealing narrow band gaps (0.52 and 0.46 eV, respectively), near-overlapping electronic transitions, and enhanced broad-spectrum light absorption in the ultraviolet region. Theoretical predictions of optical band gaps were further corroborated experimentally using Tauc’s method. Both isolated crystalline copper(II) complexes were strategically incorporated into the PVA matrix via solution casting, yielding films with bandgap energies significantly decreased from 5.8 eV (pristine) to 2.7 eV (composite). The film conductivity was analyzed by using equivalent electrical circuits and Bode plots. The potential applications of composite films for electrochemical double-layer capacitor (EDLC) devices have been assessed by cyclic voltammetry. The highest-conductivity composite was further studied and used in EDLC device fabrication, demonstrating a promising performance for such applications. Molecular dynamics simulations provided deeper insights into polymer–complex interactions that complex 2 exhibited higher adsorption energy and stronger binding affinity than complex 1.