Interfacial self-assembly of Zn(Fe)-bisterpyridine coordination polymers, their fluorescent and electrochemical properties in Langmuir-Blodgett films

Metal-bisterpyridine coordination polymers (CPs) have been synthesized at the air-water interface through an interfacial coordination reaction of metal ions (Zn2+/Fe2+) with bidentate ligand of 4,4''''(1,4-phenylene)bis(2,2':6'2 ''-terpyridine) (PBTerpy). Surface pressure-area isotherms indicated that the average molecular area of PBTerpy was about 0.8 nm(2) on the pure water surface, which slightly increased to about 1 nm(2) on the inorganic salt subphase surfaces due to the formation of Zn(Fe)-PBTerpy CPs. Monolayers of the Zn(Fe)-PBTerpy CPs were deposited on the quartz, Si and indium tin oxide (ITO) substrate surfaces by the Langmuir-Blodgett (LB) method. The as-prepared LB films were characterized by using UV-vis absorption and fluorescence spectroscopy, X-ray photoelectron spectroscopy, as well as by using scanning electron microscope and atomic force microscope. The pure PBTerpy ligand and its LB films showed a broad fluorescent emission at about 350-370 nm. This emission red shifted to about 380-410 nm in the LB films of Zn(Fe)-PBTerpy CPs. Time-resolved fluorescent spectra revealed that the emission lifetime was about 1.2-2.4 ns for the pure PBTerpy ligand in the dilute methanol solution and its LB films, while it was about 5.0 ns in the LB film of Fe-PBTerpy CPs and 20.6 ns in the LB film of Zn-PBTerpy CPs. A couple of reversible redox wave was recorded and centered at about -0.53 V (vs Ag/AgCl) for the ITO electrode covered by the LB film of Fe-PBTerpy CPs, which was designated to one electron transfer process between the CPs of Fe-(II)-PBTerpy and Fe-(III)-PBTerpy. Since the PBTerpy can coordinate with lots of transition metal ions, we suggest that the present method may be used to prepare new optically and electrically active organic-inorganic composite materials. (c) 2013 Elsevier B.V. All rights reserved.