Interfacial Engineering of Amide-Based Langmuir–Blodgett Films for Sustainable Multifunctional Applications

Abstract Amide-containing organic molecules are widely used as building blocks for ultrathin films because of their diverse intermolecular interactions and structural flexibility. In this work, four amide-based small molecules were assembled into Langmuir–Blodgett (LB) films, while Congo Red (CR), Rhodamine B (RhB), and Safranin T (ST) were added to the subphase to regulate interfacial assembly at the air–water interface. Structural characterization shows that the introduction of dyes into the subphase leads to distinct aggregation behaviors and surface morphologies in the resulting films. RhB-containing films generally tend to form more interconnected aggregate morphologies in several molecular systems. Several RhB-containing systems show higher photocurrent responses and smaller semicircle diameters in electrochemical impedance spectroscopy (EIS) measurements. CR-containing systems exhibit stronger Raman signals and more pronounced spectral variations upon exposure to acidic and basic vapors. The enhanced Raman response may be associated with local analyte accumulation, molecular interactions, and possible resonance effects under 532 nm excitation. In contrast, ST-containing systems exhibit structure-dependent behavior, resulting in distinct aggregation morphologies and photoelectrochemical (PEC) behaviors. Overall, dye-assisted interfacial engineering effectively modulates the assembly and functional responses of amide-based LB films. This work provides insights into multicomponent organic ultrathin film systems and may guide the design of sustainable photoelectrochemical materials.