Charge Transport in Supramolecular Dendro Assemblies

Molecular engineering of the interfaces in phase-separated nanomaterials is believed to be a key to the precise manipulation of supramolecular structures and their functions. Dendritic systems are attractive polymer platforms for co-assembly because their particular shape introduces curved interfaces and because large numbers of functional groups can be readily introduced into a single molecule. The use of extended amphiphilic dendrons leads to the formation of phase-separated core-shell architectures. Lithium ion doping enables charge transport studies within a nanostructured material. Although promising, the full potential of such interface engineering has not been explored especially with respect to charge transport phenomena. The underlying project thus proposes a molecular structure-property relations study including phase behaviour, morphological and rheological studies as well as charge transport behaviour. Amphiphilic macromolecules with a hydrophilic aliphatic ether based dendron with a hydrophobic aliphatic docosyl periphery will be connected with a linear poly(ethylene oxide) PEO chain. The full composition space between hydrophilic and hydrophobic segments for morphology control will be explored. Upon doping with lithium ions charge transport properties in these materials will be investigated. In order to obtain room temperature charge transport, the structures will be stabilized by freezing them through local network formation in silica-type networks. Inorganic-organic hybrid materials are obtained through a combination of organic and inorganic components via a sol-gel process where the dendritic systems act as structure directing agents. Replacing the aliphatic docosyl periphery for a hole conducting triphenylamine dendrimer and doping with lithium ions will enable ion transport in one domain and hole transport in the other domain. By keeping the triphenylamine- dendrimer unit and replacing the linear part from a PEO chain for an acrylate chain with electron conducting perylene-type substituents will result in an AB-type block-copolymer which might act as photovoltaic material. The resulting mixed conductors may find applications in light emitting electrochemical cells, electrochromic displays, or as electrochemical actuators. The present approach will enable the separation and thus independent optimization of electronic, ionic or hole transporting domains, while maximizing interfacial contact. It will also allow fine control of the shape (through phase control) and orientation (through processing) of the interfaces, ultimately leading to more sophisticated or better devices.