Hybrid polythiophene–metal composites as promising sensing materials for chemical warfare agents and chlorofluorocarbons

Abstract

The effective detection of toxic industrial chemicals and chemical warfare agents (CWAs) demands sensing materials that combine high sensitivity with low production cost. Conducting polymers such as polythiophene (PTh) offer structural flexibility, yet their intrinsic electronic properties often limit sensing performance. In this work, PTh is doped with first-row transition metals (TM = Sc–Zn), and the changes in structural stability, electronic structure, and magnetic properties are assessed using spin-polarized density functional theory (DFT). Different spin multiplicities were evaluated to identify energetically favorable configurations. Among the investigated systems, Cr@PTh (septet) and Fe@PTh (quintet) exhibit the strongest thermodynamic stability, with binding energies of −5.37 and −3.47 eV, respectively. However, the narrow energy gap in Cr limits its sensing potential, despite improved structural stability, while Fe doping provides a balanced combination of stability, electronic tunability, and reactivity, positioning Fe@PTh as the most promising candidate. Adsorption studies of Fe@PTh toward representative CWAs (HCN, NCCl, NCBr, NCCN, and AsH₃) and chlorofluorocarbons (CFC-11, CFC-12) further reveal interaction energies ranging from −2.37 to −44.79 kcal mol⁻¹. These interactions induce pronounced charge redistribution and band-gap variations of up to 0.41 eV, as supported by density-of-states and frontier-orbital analyses. Reduced density gradient (RDG) isosurface visualizations further elucidated the nature of non-covalent interactions. These results demonstrate the potential of TM@PTh composites, particularly Fe@PTh, as tunable, low-cost sensing materials capable of selectively detecting both highly reactive and environmentally persistent toxicants. This study provides a computational framework to guide the future experimental development of TM-polymer-based chemical sensors.