Synthesis and characterisation of fluorenone-thiophene based donor-acceptor oligomers: role of moiety sequence upon packing and electronic properties

A series of oligomers constituting alternating thiophene and fluorenone residues, designed to evaluate the effect upon both electronic properties and packing of the moiety sequence in the light of donor-acceptor concept, were synthesised and studied by cyclic voltammetry, optical spectroscopy, and XRD investigations into crystals, films, and powders. Moreover, ab initio calculations, based on Density Functional Theory, were carried out on selected molecules. A clear indication of close-packing induction by fluorenone in the oligomers, together with the factors determining the electrical and optical properties, are derived and presented. In the light of the performance of selected compounds in prototypes of p-type FET devices and bulk heterojunction solar cells, some general indications of chemical structure requirements for applications such as photovoltaic cells are described.