Triarylamine Substituted Arylene Bisimides as Solution Processable Organic Semiconductors for Field Effect Transistors. Effect of Substituent Position on Their Spectroscopic, Electrochemical, Structural, and Electrical Transport Properties

Abstract

New, solution processable organic semiconductors, namely arylene bisimides core- or N-functionalized with triarylamines have been synthesized in view of their potential application in organic electronics. In N-functionalized compounds the electrochemically determined oxidation potentials are 0.46 and 0.48 V vs Fc/Fc+ for perylene (P1) and naphthalene (N1) bisimides, respectively. For the core functionalized perylene bisimide (P2) this potential is shifted to higher values (0.55 V vs Fc/Fc+). A reversed trend is observed for the first reduction potential since P2 is being reduced at the lowest potential (−1.09 V) whereas N1 and P1 at −1.05 and −1.02 V, respectively. These shifts observed in the case of P2 are induced by donor–acceptor interactions between the substituent and the core. The results of DFT calculations performed for N-substituted bisimides indicate a clear separation in space of the HOMO and LUMO orbitals, the former being located on the triarylamine substituent whereas the latter is on the bisimide core. To a first approximation, their UV–vis–NIR spectra can be considered as a superposition of the triarylamine spectrum and those of bisimides containing nonchromophore (alkyl) substituents. This indicates a very weak or essentially nonexistent conjugation between the aromatic core and the N-substituents. In powders, the N-functionalized bisimides show liquid crystalline-type structural organization whereas in thin, spin-coated films they are amorphous. The core-substituted bisimide shows different properties. In this case a new band of a charge transfer (CT) character appears in its UV–vis spectrum. In accordance with the spectroscopic data, the DFT calculations indicate that in the core-substituted compound the HOMO electron density spreads from the triarylamine substituent to the bisimide core. Powders of the core-substituted bisimide crystallize in a 3D structure whereas thin spin-coated films show liquid crystalline-like structural organization. Taking into account their electrochemical properties, all three bisimides studied seem to be good candidates for the fabrication of air operating ambipolar transistors. However, N-functionalized bisimides show only p-type behavior with the hole mobility approaching 10–4 cm2 V–1 s–1 in the all organic (CYTOP dielectric) field effect transistor configuration. The core-substituted bisimide shows, however, the expected ambipolar behavior with the hole and electron mobilities of 1.5 × 10–3 and 3.5 × 10–4 cm2 V–1 s–1, respectively.