Fabrication and optoelectronic properties of novel films based on functionalized multiwalled carbon nanotubes and (phthalocyaninato)ruthenium(II) via coordination bonded layer-by-layer self-assembly.

4-(2-(4-pyridinyl)Ethynyl)benzenic diazonium salt (PBD) was used to modify multiwalled carbon nanotubes (MWCNTs) by the self-assembly technique. After the decomposition of the diazonium group in PBD under UV irradiation, the PBD monolayer film covalently anchored on multiwalled carbon nanotubes is very stable. The obtained pyridine-modified MWCNTs (Py(Ar)-MWCNTs) have good solubility in common organic solvents. Furthermore, the layer-by-layer (LBL) self-assembled fully conjugated films of Py(Ar)-MWCNTs and (phthalocyaninato)ruthenium(II) (RuPc) were fabricated on the PBD-modified substrates, and characterized using UV-vis absorption spectroscopy, scanning electron microscopy (SEM), and electrochemistry. The UV-vis analysis results indicate that the LBL RuPc/Py(Ar)-MWCNTs self-assembled multilayer films with axial ligands between the ruthenium atom and pyridine group were successfully fabricated, and the progressive assembly runs regularly with almost equal amounts of deposition in each cycle. A top view SEM image shows a random and homogeneous distribution of Py(Ar)-MWCNTs over the PBD-modified silicon substrate, which indicates well independence between all Py(Ar)-MWCNTs. Moreover, the opto-electronic conversion was also studied by assembling RuPc/Py(Ar)-MWCNTs multilayer films on PBD-modified ITO substrate. Under illumination, the LBL self-assembled films on ITO showed an effective photoinduced charge transfer because of their conjugated structure and the ITO current density changed with the number of bilayer. As the number of bilayers was increased, the photocurrent increases and reaches its maximum value (∼300 nA/cm(2)) at nine bilayers. These results allow us to design novel materials for applications in optoelectronic devices by using LBL self-assembly techniques.

Fabrication, electrochemical, and optoelectronic properties of layer-by-layer films based on (phthalocyaninato)ruthenium(II) and triruthenium dodecacarbonyl bridged by 4,4'-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(4,4'-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 self-assembled 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 AFM images 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 (approximately 150 nA/cm2) at six bilayers. A further 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.