Polymorph, assembly, luminescence and semiconductor properties of a quinacridone derivative with extended π-conjugated framework

Abstract

The structures and properties of an indole-ring-fused quinacridone derivative 5,8,15,18-tetraoctyl-5,8,15,18-tetrahydroindolo[3,2-a]indole[3′,2′ : 5,6]quinacridone (IDQA), which was synthesized by an improved procedure, have been carefully investigated and compared with its parent compound N,N′-di(n-octyl)quinacridone (C8-QA). Concentration-dependent ¹H NMR spectra revealed that the strong aggregations of IDQA existed in solution because of the flat and extended π-conjugation. Two polymorphs of IDQA with and without π⋯π interactions exhibited red and non emissions, respectively. One-dimensional micromaterials with different morphologies constructed by IDQA molecules were fabricated by a reprecipitation approach and they displayed different emission properties due to the different molecular packing. The nine-ring fused flat skeleton endowed this material with several elegant properties, including a high photoluminescent quantum yield in solution, and a high thermal and electrochemical stability. Therefore, the efficient doped organic light emitting device (OLED) with IDQA as the emitter was fabricated. Moreover, the large π-conjugation system endowed the IDQA thin film with ordered molecular packing and good hole transport properties (hole mobility μ_h = 0.047 cm² V⁻¹ s⁻¹).