Fabrication, electrochemical, and optoelectronic properties of layer-by-layer films based on (phthalocyaninato)ruthenium(II) and triruthenium dodecacarbonyl bridged by 4,40-bipyridine as ligand

4-(2-(4-Pyridinyl)ethynyl)benzenic diazonium salt (PBD) was synthesized and used to modify the substrate by self-assembly (SA) technique. Following decomposition of the diazonium group in PBD under UV irradiation, the ionic bonds between the diazonium salt and substrate are converted to covalent bonds. The PBD monolayer film anchored on substrates is very stable. Furthermore, the layer-by-layer (LBL) self-assembled films of bis(4,40-bipyridine)- (phthalocyaninato)ruthenium(II) (RuPc(bipy)2, BPR) and triruthenium dodecacarbonyl (Ru3(CO)12, TRDC) were fabricated on the PBD-modified substrates and characterized using UV-vis absorption spectroscopy, atomic force microscopy (AFM), and electrochemistry. The UV-vis analysis results indicate that the LBL TRDC-BPR selfassembled multilayer films with axial ligands between ruthenium atoms and pyridine groups were successfully fabricated and the progressive assembly runs regularly with almost equal amounts of deposition in each cycle. The AFMimages of the seven-bilayer TRDC-BPR film on silicon wafer showed round-shaped small domains with sizes of 30-40 nm. The values of the energy band gap (Eg), the highest occupied molecular orbital (HOMO), and the lowest unoccupied molecular orbital (LUMO) of six-bilayer TRDC-BPR on indium-tin-oxide (ITO) glass slides were measured using the UV-vis absorption spectrum and a cyclic voltammogram with values of 1.8, -5.0, and -3.2 eV, respectively. Under illumination, the self-assembled film on ITO showed effective photoinduced charge transfer and changed the current density. As the number of bilayers was increased, the photocurrent increased and reached its maximum value (~150 nA/cm2) at six bilayers.Afurther increase in the number of bilayers led to a decrease in current due to the increase in cell resistance. The results allow us to design new materials with higher performance for optoelectronic applications.