Synthesis, size-dependent optoelectronic and charge transport properties of thieno(bis)imide end-substituted molecular semiconductors

The synthesis of two new thieno(bis)imide (TBI, N) end functionalized oligothiophene semiconductors is reported. In particular, trimer (NT3N) and pentamer (NT5N) have been synthesized and characterized. Two different synthetic approaches for their preparation were tested and compared namely conventional Stille cross coupling and direct arylation reaction via C-H activation. Theoretical calculations, optical and electrochemical characterization allowed us to assess the role of the pi-conjugation extent, i.e., of the oligomer size on the optoelectronic properties of these materials. In both TBI ended compounds, due to the strong localization of the LUMO orbital on the TBI unit, the LUMO energy is almost insensitive to the oligomer size, this being crucial for the fine-tailoring of the energy and the distribution of the frontier orbitals. Surprisingly, despite its short size and contrarily to comparable TBI-free analogues, NT3N shows electron charge transport with mobility up to mu(N) = 10 (4) cm(2) V (1) s (1), while increasing the oligomer size to NT5N promotes ambipolar behavior and electroluminescence properties with mobility up to mu(N) = 0.14 cm(2) V (1) s (1) and to mu(P) = 10 (5) cm(2) V (1) s (1). (C) 2013 Elsevier B.V. All rights reserved.