Hydrogen bonding network formed between accumulated Langmuir-Blodgett films of barbituric acid and triaminotriazine derivatives

Accumulated Langmuir-Blodgett (LB) films that consist of two layers of barbituric acid (BA) and triaminotriazine (TAZ) derivatives (C₁₈BA and 2C₁₈TAZ) were deposited at various surface pressures on a gold-evaporated glass slide covered with a deuterated cadmium stearate (CdSt-d₃₅) monolayer. The two-monolayer LB films (the CdSt-d₃₅ layer is considered to be a part of the substrate) were measured by infrared reflection-absorption (IRRA) spectrometry to investigate the hydrogen-bonding network formed between the two layers. The most notable results were given by the LB film that has the layer configuration of IR// C₁₈BA/2C₁₈TAZ/CdSt-d₃₅/Au. The C₁₈BA layer was deposited at various surface pressures on the 2C₁₈TAZ monolayer. Depending on the surface pressure, the wavenumber of the C=O stretching vibration band (v-(C=O)), derived from BA, showed drastic change. At 20 mN m^-1, the C=O groups were found to be in non-hydrogen bonded state (1755 cm^-1) to a large extent. The non-hydrogen bonded C=O groups are, in general, rarely seen for the interacted BA/TAZ system. The extraordinary non-hydrogen bonded C=O groups were explained readily by a novel schematic model that was estimated through the molecular orientational analysis. In consequent, the film-to-film interaction is found to give a quite unique hydrogen bonding network structure.