Fabrication and optoelectronic conversion of layer-by-layer self-assembly films based on terpyridines and metal ions on surface of substrate modified by diazoresin and 4-formylbenzoic acid

To enhance the stability of the layer-by-layer (LBL) self-assembled films fabricated from terpyridines and ruthenium ions, a new method of introducing mono-terpyridinyl groups onto the surface of substrates was designed in this paper. First, diazoresin (DR) and sodium salt of 4-formylbenzoic acid (FBA) were successively deposited on the surface of substrate by self-assembly (SA) technique. Following decomposition of the diazonium group in DR under UV irradiation, the ionic bonds between substrate, DR and FBA were synchronously converted to the covalent bonds. Furthermore, the terpyridinyl groups were introduced onto the outmost surface through the Schiff base reaction between 4′-(4-amino-phenyl)-2,2′ :6′ ,2″-terpyridine (Atpy) and formyl groups in DR-FBA. So that, the DR-FBA-Atpy monolayer film anchored on substrate was formed and very stable, which achieved the modification to substrates and provided active sites to coordinatively react with ruthenium ions. Consequently, diffluent 1,4-bis(2,2′ :6′, 2″- terpyridine-4-yl)benzene (Bi-tpy) and RuCl₃ multilayer films were formed on the DRFBA-Atpy monolayer through coordination bonds based on LBL self-assembled technique. The UV-Vis analysis results indicated that the LBL Bi-tpy/RuCl₃, self-assembled multilayer films were successfully fabricated and the progressive assembly ran regularly with almost equal amounts of deposition in each cycle. The AFM images of the 4-bilayer Bi-tpy/RuCl ₃, film on silicon wafer showed round-shaped small domains with size of 25 nm. Under illumination, the self-assembled film on ITO showed effective photoinduced charge transfer. A linear relationship between conversion efficiency and the number of bilayers was discussed.