Molecular semiconductors with Carbazole versus Triazatruxene endcaps: A matter of self-assembly

Abstract

In this work, we describe the design and synthesis of a novel soluble conjugated molecule, CAR-TzDPP, consisting of a central diketopyrrolopyrrole core (DPP) connected to carbazole endcaps through thiazole rings. To evaluate its properties, a triazatruxene-based molecule (TAT-TzDPP) was used as a model for comparison. The electrochemical and the in-solution optical properties are in good agreement with those obtained from DFT calculations. However, the thin-film self-assemblies of CAR-TzDPP exhibited distinct differences, forming a more standard crystalline structure including insulating side-chains layers that disallowed side interactions between aromatic rings. This resulted in a reduced charge transport ability to a two-dimensional (2D) ambipolar charge transport in CAR-TzDPP, compared to the nearly isotropic unipolar charge transport in TAT-TzDPP. Despite this, CAR-TzDPP can be considered a viable alternative for device configurations requiring semiconducting pathways aligned in the substrate plane due to its simplified and high yield synthesis route, ease of processing, and reliable charge mobility in OFETs. This research highlights the significance of molecular units in small semiconducting organic molecules, not only in terms of their individual optoelectronic properties but also in terms of their self-assembly capabilities, which ultimately influence their charge transport properties.