Suitability of 3,4 dialkyl substitution in molecular crystal based on thiophene-fluorenone for organic field effect transistors

A new co-oligomer constituted by both a thiophene sequence bearing a 3,4-dialkyl substitution, imparting processability, and by end-capping fluorenone moieties, has been synthesised. The molecule, potentially suitable for close-packing aptness, has been characterized by means of combined optical, thermal, structural, and morphological analyses, showing that, despite the O–H intermolecular interaction favoured by fluorenone presence, the large steric hindrance specific to the dialkyl 3,4-disubstitution strongly limits the intermolecular interaction. Hence it makes such substitution pattern unsuitable for field effect transistor application, as it is confirmed by the electrical performances measured on prototype devices.