Molecular organization and effective energy transfer in iridium metallosurfactant–porphyrin assemblies embedded in Langmuir–Schaefer films

Abstract

Mixed Langmuir monolayers and Langmuir–Schaefer (LS) films containing the cationic metallosurfactant bis(2-phenylpyridine)(4,4′-diheptadecyl-2,2′-bipyridine)-iridium(III) chloride (Ir-complex) and the anionic tetrakis(4-sulfonatophenyl)porphyrin (TSPP) in 4 ∶ 1 molar ratio have been successfully prepared by the co-spreading method at the air–water interface. The presence of both luminescent species at the interface, as well as the organization of the TSPP underneath the Ir-complex matrix in Langmuir and LS films, is inferred by surface techniques such as π–A isotherms, reflection spectroscopy, Brewster angle microscopy (BAM) and UV–visible absorption spectroscopy. A red-shift in the absorption band of the porphyrin under the compression of the mixed monolayer suggests the J-aggregation of the TSPP under the Ir-complex matrix. To date, this is the first report of Langmuir and/or LS films containing these two types of species together. Furthermore, the intermolecular energy transfer between Ir-complex and TSPP molecules in solution and in transferred mixed films is investigated through steady-state fluorescence and lifetime measurements. These results indicate that effective intermolecular energy transfer occurs from the Ir-complex to the TSPP molecules in LS films. The influence of the spatial proximity of donor and acceptor molecules has been studied by the insertion of lipid interlayers among them.