Preparation of highly pure quaterthiophene and role of impurities on its photoluminescence properties

Highly pure quaterthiophene (4T) has been prepared from monobromobithiophene by a Ni0-mediated coupling reaction. The analysis of impurities produced by the synthetic procedure, performed by mass spectrometry and gas chromatography with a mass spectrometer detector, has allowed the identification of at least four contaminants, among them, α-bromoquaterthiophene (Br-4T). Studies of photoluminescence carried out at low temperatures (from 70 to 4 K) on 4T thin films grown by organic molecular beam deposition are demonstrated to be a powerful tool in detecting impurities that can act as traps for 4T emission. Indeed, it was possible to assign the anomalous emission observed in some 4T thin films to Br-4T. A protocol for removal of 4T contaminants is also proposed.