Effects of click postfunctionalization on thermal stability and field effect transistor performances of aromatic polyamines

Abstract

Tetracyanoethylene (TCNE) was stepwise added to the side chain alkynes of aromatic polyamines undergoing a click chemistry-type addition reaction via a [2 + 2] cycloaddition followed by a cycloreversion process. The quantitative addition was confirmed by the comprehensive spectroscopic analyses of the full TCNE adducts. An X-ray crystallographic analysis revealed the polymerization incapability of the TCNE-adducted aromatic amine monomers due to the decreased basicity of the amino group. This fact indicated that the click postfunctionalization is an alternative and useful method for obtaining the desired polymers. The efficient intramolecular donor–acceptor interactions were elucidated from the appearance of the charge-transfer bands as well as the fluorescence quenching. When the dimethylamino donors are positioned at the polymer side chains, the appropriate donor–acceptor balance is achieved, resulting in the enhancement of the thermal properties. Thus, as more TCNEs were added, both the decomposition and glass transition temperatures of the aromatic polyamine gradually increased. A careful analysis of the differential pulse voltammogram (DPV) curves also revealed the gradual cathodic shifts in both the oxidation and reduction potentials with the TCNE addition amount. This result suggested that the polymer energy levels, namely the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels, can be lowered by the added TCNE amount. Their thin film transistors were fabricated, and a clear correlation between the polymer energy levels and hole mobilities was demonstrated.