Hybrid layer-by-layer films based on lanthanide-bridged silicotungstates and poly(ethylenimine)

Hybrid multilayer films composed of poly(ethylenimine) and sandwich-type silicotungstates, K13[Ln(SiW11O39)2] (Ln(SiW11)2), Ln3+ = Eu, Tb, Dy, were prepared on glassy carbon electrodes, quartz and glass slides using the electrostatic LbL self-assembly method. The film build up, monitored by electronic spectroscopy, showed a regular stepwise growth indicating a strong interaction between layers. The X-ray photoelectron spectroscopy measurements corroborated the successful fabrication of the hybrid films with the PEI–POMs composition and pointed out that the intrinsic charge compensation from the film components is the major contribution, although there is some extrinsic charge compensation from the counter cations from the POMs and electrolyte. All the LbL films showed W-based reduction processes due to the immobilized POMs; voltammetric responses revealed a kinetic facilitation of the first reduction process in the immobilized Tb(SiW11)2 and Dy(SiW11)2 polyanions relatively to the free POMs and scan rate effect showed that the tungsten reduction process for all POMs is surface-confined. The photoluminescence properties of PEI/Eu(SiW11)2 multilayer films were investigated and showed the characteristic Eu3+ emission pattern.