The catalyst-free green synthesis and QTAIM analysis of anilino-1,4-naphthoquinones as molecular wires

Abstract

Molecular wires represent a cornerstone of next-generation nanoelectronics, yet the design of highly efficient, short molecular conductors remains a significant challenge. In this study, we present a catalyst-free, green synthetic route for the preparation of anilino-1,4-naphthoquinone enaminone derivatives via aqueous-phase Michael addition between anilines and 1,2-naphthoquinone-4-sulfonic acid sodium salt. The reaction proceeds rapidly at room temperature, yielding products with excellent efficiency (96–98%) and exceptional purity, as confirmed by comprehensive spectroscopic characterization (FT-IR, UV-Vis, 1H and 13C NMR, MS) and elemental analysis. Single-crystal X-ray diffraction further validated the molecular structures of representative compounds. Theoretical investigations using Density Functional Theory (DFT) and Quantum Theory of Atoms in Molecules (QTAIM) provided deep insights into the electronic properties and charge transport behavior of these systems. Key analyses included cohesive energy calculations, UV-Vis exciton energy profiles, frontier molecular orbital energies (HOMO/LUMO), chemical reactivity descriptors (hardness, softness, chemical potential), and dipole moment variations under external electric fields (0-140 × 10− 4 a.u.). Additionally, localized orbital locator (LOL) contours, electron density Laplacians, and current-voltage (I–V) characteristics based on Landauer theory were evaluated to assess charge transport efficiency. Comparative analysis reveals that extending the π-conjugation in a molecular system markedly improves its electronic properties, leading to lower energy gaps, enhanced conductance, and greater field responsiveness, which are critical for molecular wire functionality. Furthermore, this work combines sustainable synthesis with advanced computational modeling to offer a robust framework for the design and evaluation of short molecular wires for nanoelectronic devices.