A straightforward synthetic strategy towards conjugated donor-acceptor naphthylimido-azomethines with tunable films morphologies and opto-electronic properties

Abstract

An important challenge in organic electronic applications is to control the molecular assembly pathway towards organic coatings with desired morphologies. Here, new donor-acceptor napththylimido-azomethine oligomers with triphenylamine or carbazole as electron-donor unit are synthesized and investigated for their opto-electronic properties, with focus on the effect induced by morphological features. A novel structural pattern is approached, with naphthylimide and azomethine directly linked through NN bond. When oligomer films are prepared from different solvents by drop-casting and spin-coating techniques, rectangular sheets, worm-, island- or granular-like morphologies evolve, in conjunction with the molecular structure and processing conditions. Besides high thermal stability, the oligomers display overlapped localized and intramolecular charge transfer transitions involving main and degenerated molecular orbitals, which enable fluorescence modulation in dependence on solvent polarity. With the energy band gap sensitively tailored by the structural elements and solid state molecular packing, the coatings sustain ambipolar charge transport and can be used as n- or p-type active layers in opto-electronic applications. These results confirm that the molecular design is a powerful tool to fine-tune the molecular assembly of organic donor–acceptor molecules and their corresponding opto-electronic features.