Bifacial dye membranes: ultrathin and free-standing although not being covalently bound
in: Advanced Materials (2023)
Layers of aligned dyes are key to photo-driven charge separation in dye sensitized solar cells, but cannot be exploited as rectifying membranes in photocatalysis to separate half-cells because they are not sufficiently stable. While impressive work on the fabrication of stable noncovalent membranes has been recently demonstrated, these membranes are inherently suffering from non-uniform orientation of the constituting dyes. To stabilize layers made from uniformly assembled and aligned dyes, they can be covalently cross-linked via functional groups or via chromophores at the expense of their optical properties. Here we report stable membranes from established dyes that do not need to be elaborately functionalized nor do their chromophores need to be destroyed. These membranes are free-standing, although being only non-covalently linked. To enable uniform dye-alignment, we used Langmuir layers made from linear, water-insoluble dyes. We demonstrate that water-soluble charge transfer dyes adsorb onto and intercalate into the Langmuir layer from the aqueous subphase, thus yielding free-standing, molecularly thin membranes. The developed bifacial layers consist almost entirely of π-conjugated units and thus can conduct charges and can be further engineered for optoelectronic and photocatalytic applications.