Eco-friendly one-pot synthesis, structural, and physical properties of coumarin 6

This study introduced an environmentally friendly, one-pot synthesis of coumarin 6 (C6) conducted at room temperature in water. The synthesis involved the Knoevenagel condensation of 2-(benzo [d] thiazol-2-yl) acetonitrile (1) and 4-(diethylamino)-2-hydroxybenzaldehyde (2). The method was notable for its mild reaction conditions, high yield, atom efficiency, environmental friendliness, straightforward product isolation without column chromatography, clean reaction profiles, and scalability. A detailed analysis was conducted to explore the effects of thickness on C6 thin films deposited using vacuum thermal deposition on flexible polyethylene terephthalate substrates. X-ray diffraction demonstrated that film thickness considerably impacted structural parameters. Atomic force microscopy showed that surface roughness increases with layer thickness. Raman spectra confirmed the characteristic vibrations of intermolecular bonds in C6 in powder form and thin films. Optical studies revealed that the thin films exhibit an indirect allowed transition with two optical energy gaps. It was also observed that the energy gap decreases as the thickness of the thin films increases. Photoluminescence studies indicated that increased film thickness results in higher emission intensity and a broader emission range, with a prominent emission peak at (550–558 nm). The optical constants, dielectric constants, and nonlinear optical properties of C6 thin films were examined and discussed as a function of the thickness. The comprehensive characterization of the structural, surface morphological, and optical properties of C6 thin films highlights their potential for use in flexible electronics, offering important insights into their optical reliability.