Nafion Films – Modulating Color Emissions

Researchers employed Nafion as a solid medium for the fabrication of transparent luminescent materials with tunable emissions. These membranes are quite famous for their ability to conduct protons and exchange cations. Nafion is composed of hydrophobic main chains and pendant hydrophilic side chains.

The side chains are especially important. When Nafion is introduced to a polar solvent, solvent molecules are surrounded by side-chain sulfonic acid groups. Cavities ∼4 nm in diameter form in it when it is swollen with water or alcohol and large molecules can be immobilized within them. Moreover, the proton conductivity of hydrated Nafion is very high and can reach up to 0.1 S cm−1.7d A variety of functional films have been developed by using Nafion to take advantage of these properties.

The researchers first synthesized and crystallized the HPBA–TbIII and HPBA–EuIII complexes [TbIII2(PBA)6] and [EuIII2(PBA)6] as pH-sensitive emitters. The complexes were easily incorporated into transparent Nafion film, and the excellent proton conduction in Nafion not only made it responsive to pH; the proton gradient within a [LnIII2(PBA)6]@Nafion. They demonstrated a fine-tuning of emission color in the transparent film by adjusting its pH with buffer solutions and manipulating the electric field.

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