Highly luminescent Langmuir–Blodgett films of amphiphilic Ir(iii) complexes for application in gas sensing

Four members of mixed ligand cyclometalated iridium(III) complexes, fac-[Ir(ppy)nL3−n] (ppy = 2-phenylpyridine; L = 2-(3-octadecyloxyphenyl)pyridine; n = 0–3), were prepared in a one-pot reaction between [Ir(ppy)2(O⁁O)] (O⁁O = acetylacetonato) and LH in glycerol at 170 °C. Each compound was purified and optically resolved to Δ- and Λ-enantiomers chromatographically on a chiral column. A film of fac-[Ir(ppy)nL3−n] floating at an air–water interface was transferred horizontally onto a hydrophobic glass plate as a Langmuir–Blodgett (LB) film. The emission from a single layered LB film was monitored under the atmosphere of various kinds of gases. As a result, molecules with functional groups such as –OH, CO and –CN were found to quench efficiently excited fac-[Ir(ppy)nL3−n] in a film. The effects of isotope and molecular chirality on energy transfer were also investigated, comparing the quenching ability between H2O and D2O or between R-2-butanol and S-2-butanol on a racemic or chiral film of fac-[Ir(ppy)2L], respectively.