Palmitic acid and aquo-ruthenium complex monolayers at the liquid–air interface and electroactive Langmuir–Blodgett films

Abstract

Liquid monolayers and Langmuir–Blodgett (LB) films of palmitic acid and Ru[L(4′-topty)(H2O)] (ClO4)2 (L=(C6H5)2PCH2CH2P(C6H5)2; 4-totpy= 4′-(4-tolyl-2,2′:6′,2″-terpyridine)) have been produced. Comparison of pressure–area and surface potential–area curves for pure palmitic acid monolayers and the mixed films of palmitic acid with ruthenium complex indicates that the minimum molecular area is determined only by the fatty acid. However, the metal complex bonding increases the monolayer compressibility, transforming the condensed state to expanded at higher area per molecule. The absence of any contribution of the metal complex to the minimum molecular area for the mixed films suggests that the complex may be ion paired with the hydrophilic head group of palmitic acid molecules at the condensed state. This observation is confirmed in the FTIR spectrum of the transferred films, by the absence of CO dimer stretching at 1700cm−1 suggesting the formation of the salt in the mixed films. The electronic spectra and cyclic voltammograms show the presence of the ruthenium complex in the films.