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

Abstract

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 0.8nm2 on the pure water surface, which slightly increased to about 1nm2 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 350–370nm. This emission red shifted to about 380–410nm in the LB films of Zn(Fe)-PBTerpy CPs. Time-resolved fluorescent spectra revealed that the emission lifetime was about 1.2–2.4ns for the pure PBTerpy ligand in the dilute methanol solution and its LB films, while it was about 5.0ns in the LB film of Fe-PBTerpy CPs and 20.6ns in the LB film of Zn-PBTerpy CPs. A couple of reversible redox wave was recorded and centered at about −0.53V (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.