Synthesis, structural elucidation and optical activity of symmetric Schiff base-functionalized ferrocenes: Synergetic experimental and DFT insights

Abstract

A number of Schiff base functionalized derivatives (3a-c) was synthesized from the conventional dehydration of ferrocenecarboxaldehyde and diamine precursors in acetonitrile as a solvent at ambient conditions. IR, UV–Vis, elemental analysis, 1H- and 13CNMR were used to elucidate the novel bis-Schiff base compounds. The nature of electronic absorptions was tracked using Time-Dependent Density-Functional Theory (TD-DFT). The molecular electrostatic potential illuminated that the target compounds are sharing relatively akin electronic distributions. In order to determine the electrophilic and nucleophilic sites, surface analysis of the structures was examined for this purpose. These sites are expected to possess an indispensable role to stabilize and robust the structures via typical hydrogen bonding and non-classical CH···π interactions. Type and influence of solvents on absorption spectra were pursued for the selected model (3a), in which aprotic solvents showed negative solvatochromism (more stable ground state), whereas protic solvents delivered positive solvatochromism (more stable excited state). For example, the metal-to-ligand charge transfer band displayed a gradual shift of the λmax (12 nm) when the type of solvent was switched from polar aprotic (ethyl acetate) to polar protic (methanol) due to the formation of hydrogen bonding, causing bathochromic shift. Eventually, the computationally resulting energy gap of the new products (ΔE) were found to be −4.258 (3a), −4.022 (3b) and −3.105 (3c) eV. These values were compared and found to be in a close level with produced figures from the spectra of density of states and with experimentally determined values using Tauc approach.