Photo-Responsive Luminescent Lanthanide Complexes

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Photo-switches are chemical compounds that can switch between two stable forms when light is shone onto the compound. A common example is a class of compounds called azobenzenes. They work similarly to a light switch on the wall, when the stimulus is applied this induces a change. In the case of a switch in your home the stimulus is your hand and the change is whether the light is switched on or off. Whereas with the photo-switch, the light is the stimulus and the output is, in the case of azobenzene molecules, a change in length of the compound. Photo-switches have functions in sensors, electronic devices, and in medical and biological applications. For example drug release could be stimulated by light or the mechanisms involved in responsive biological systems, such as ion channels, can be further understood. Using photo-switches within a more complicated system can lead to control over the forms of photo-switch present and thus their interactions with other compounds in the system.Lanthanides are a group of elements which have unique properties. One property is long- lived luminescent (the ability to emit light), in comparison to the luminescence of biological species. Research has found that this luminescence can be controlled by the presence of other compounds (chromophores) which can either change the intensity of the luminescence or turn off the luminescence completely. This switchable property means that emission can be turned on or off depending on the nature and state of the interacting chromophore. This makes them exciting compounds for bio-imaging. Their optical properties also make them attractive compounds for optic-electronic devices, such as screens and displays.The aim of this project is to engineer a system in which the azobenzene photo-switch influences the luminescence of the lanthanide. For this to work, energy transfer between the two species must occur. Energy transfer can either happen through space and is dependent on how close the two species are relative to each other (Forster Resonance Energy transfer) or directly though a bond attaching the two species together (Dexter Energy transfer). Understanding and determining the mechanism of energy transfer aids in the engineering of a switchable luminescent lanthanide complex. In addition, the type of azobenzene and lanthanide chosen need to be considered. Recently azobenzenes have been discovered that switch length when visible light is shone onto them, these are promising candidates as visible light is much less destructive to surrounding enviroments than UV-light. The lanthanide chosen must have good luminescent properties and in order to work well with the azobenzene it must be able to absorb/emit light in a similar range to the light that induces switching in the azobenzene.Combining azobenzene photo-switches and lanthanide complexes is a new area in chemistry. Both separately are well researched, however there has only been a few examples when the two have been combined in a single system. Through synthesising a new photo-responsive lanthanide complex, in which the luminescence can be influenced by the length of the azobenzene leads to the possibility of many new and exciting discoveries. This project falls within the ESPRC physical sciences research area.