Synthesis and DFT Study of New Pyrano[3,2-c]Quinoline Derivatives for Antioxidant, Forensic, and Security Ink Applications

Abstract

Abstract A series of heterocyclic derivatives incorporating the pyrano[3,2-c]quinoline-2,5-dione framework were successfully synthesized via nucleophilic substitution reactions of 6-ethyl-4-chloropyrano[3,2-c]quinoline-3-carbaldehyde 2 with several sulfur nucleophiles. Furthermore, aldehyde 2 underwent condensation reactions with various nucleophilic reagents, such as primary amines, and selected cyclic and acyclic active methylene compounds. The optimized geometrical structure of the starting aldehyde 2 was obtained through density functional theory (DFT) calculations performed at the B3LYP/6–311++G(d,p) level of theory. These computations were employed to evaluate several molecular parameters, including the molecular electrostatic potential (MEP), Fukui functions, frontier molecular orbital (FMO) characteristics, and nuclear magnetic resonance (NMR) properties. The DPPH radical scavenging activity of all synthesized derivatives was evaluated using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. The results revealed that compounds 4, 7, and 9 exhibited the highest radical scavenging activity among the synthesized derivatives, although their activity remained lower than that of ascorbic acid. PL emission spectra and CIE 1931 chromaticity coordinates confirmed tunable fluorescence across the synthesized compounds, governed by molecular structure and physical state. Compounds 5 (yellow–green) and 6 (gold–yellow) proved highly effective for latent fingerprint visualization, yielding sharp ridge details on porous, nonporous, and multicolored substrates. Additionally, compounds 11 (violet), 8 (blue), and 3 (green–yellow) were formulated into stable, humidity-resistant luminescent inks, highlighting strong potential for anticounterfeiting and secure data encoding. GRAPHICAL ABSTRACTChemical structures linked to a flask showcasing antioxidant activity and security ink applications.The figure illustrates a synthesis process with a central flask containing red liquid, linked to chemical structures and various applications. On the left, a compound labeled "2" and additional reagents like KSCN are shown. A table on the top right details IC50 values for antioxidant activity of several compounds, while the bottom right features fingerprint images displaying three levels of detail. Images of security inks on different surfaces highlight their practical applications, showcasing blue and green-yellow inks and how they glow on various materials.