Klaus Müllen

Dibenzo[hi,st]ovalene (DBOV) is a nanographene with a combination of zigzag and armchair edges, consisting of 38 sp² carbons. Excellent optical properties with strong red emission have been demonstrated. Here we report the regioselective bromination of DBOV bearing two mesityl groups (DBOV‐Mes) by treatment with N‐bromosuccinimide (NBS) under mild conditions. The dibrominated DBOV was further subjected to transition‐metal‐catalyzed cross‐coupling reactions, that is, Suzuki and Sonogashira coupling, demonstrating the edge‐decoration of DBOV with different functional groups. Notably, DBOVs arylated at the bay regions showed intense red emission and enhanced fluorescence quantum yields of up to 0.97. Amphoteric reduction and oxidation behavior were observed by cyclic voltammetry (CV) measurements. Chemical oxidation to stable radical cation species was also demonstrated, followed by reduction back to their neutral species.

Ordering π‐systems into defined supramolecular structures is important for the development of organic functional materials. In recent years, peptides with defined secondary structures and/or self‐assembly properties were introduced as powerful tools to order peptide–chromophore conjugates into different morphologies. This work explores whether or not the directionality of peptides can be used to control the self‐assembly. The position of the π‐system in conjugates between oligoprolines and perylene monoimide (PMI) chromophores was varied by attaching the PMI moiety to the second‐to‐last residue from the C‐ and N‐termini, respectively. Microscopic and diffraction analysis revealed that the positional isomers form distinctly different supramolecular architectures that extend into the micrometer regime. NMR spectroscopic studies in solution phase allowed correlation of the self‐assembly properties with markedly different conformational preferences of the isomeric building blocks. These insights enabled the design of building blocks with predictable self‐assembly properties. Thus, the directionality of peptides offers exciting opportunities for controlling the self‐assembly and electronic properties of π‐systems.

In this tutorial review, different film microstructures, commonly termed morphologies, into which the organic semiconductor polymers self-assemble macroscopically are presented, together with their corresponding influence on charge carrier mobility and hence transistor behaviour. It will be clarified how various chemical design approaches and solution processing methods enable the manipulation of polymer morphology, leading to improvements in transistor performance. Ultimately, it is illustrated that the directional alignment of polymers form oriented fiber-like films, yielding one of the highest mobilities reported so far for polymer transistors. Based on these observations, a prediction is made concerning which kind of morphology is expected to reach the best charge carrier mobility.