Crystalline metal organic frameworks containing organic semiconductors

Metal organic frameworks (MOFs) have applications from gas storage through catalysis to the destruction of chemical warfare agents. Most of the work around the world into MOFs is almost exclusively in solution environments. This leads to MOFs structures which are either macroscopic single crystals, powders comprised of small crystallites or a mixture of the two. In final devices and, eventually, products for real world use these are not the most useful forms of MOFs as making devices around them or re-processing them is costly and time consuming. Some of the most useful morphologies of active materials for real world use are thin films – both because they use much less material than large crystals and because they have large surface area to total volume ratios. This is well demonstrated by light emitting diodes (LEDs) and organic light emitting diodes (OLEDs) which can be found in monitors, mobile phones and other display technologies. In these devices, layers of a few hundreds of nanometres do all the ‘work’. Organic semiconductors are, as demonstrated in the OLED example above, useful and commercially relevant materials which can be viewed as a replacement for existing semiconductors which are mostly comprised of inorganic elements. Integrating these kinds of molecules into MOFs allows the MOFs themselves to be made semiconducting and may enable their integration in to sensing or light emitting devices. In this project, they will be used as precursor materials to construct the above-mentioned MOFs through in-vacuum evaporation methods (described below).

We have developed a unique method to produce thin films of MOFs by evaporating starting materials in vacuum such that they crystallise together in thin films (~1-10 nm) on a variety of solid surfaces. While we have exciting preliminary data, we now need to understand why this method works and how we can optimise it to produce highly crystalline films on a variety of surfaces.
The project will comprise the growth (in vacuum) and characterisation of MOF films by a selection of complementary techniques which will probe their crystal structure, surface morphology and properties. Some of these techniques will be conducted in the same vacuum environment in which the films are grown, and others will require the use of specialised equipment which operates in ambient atmospheres. By varying experimental parameters, it is expected that the structure and properties of MOF films can be controlled and demonstrating this will be an exciting next step toward understanding and employing a brand-new synthesis method for MOFs.