Roles of Flexible Chains in Organic Semiconducting Materials

Abstract

In the past couple of years, remarkable progress has been made in solution-processable organic semiconducting materials for optoelectronics. The development of novel πconjugated backbones has always been the central issue in this field. In contrast, flexible side chains are less developed and usually used only as solubilizing groups. In this Perspective, we highlight the effects of the flexible chains in organic semiconductors, including the influences of length, odd−even effect, substitution position, terminal groups, branching position, and chirality of alkyl chains, as well as some significant features of oligo(ethylene glycol) and fluoroalkyl chains. Although the roles of flexible chains in organic semiconducting materials are complex and differ when corresponding conjugated skeleton changes, in this Perspective, we emphasize the synergy of conjugated backbones and flexible side chains, which might significantly facilitate the understanding of the roles of flexible chains in structure−property relationship and promote the development of high-performance organic semiconductors.

Effects of branching position of alkyl side chains on ordering structure and charge transport property in thienothiophenedione- and quinacridone-based semiconducting polymers

“…However, regiorandom P3ATs (raP3ATs) exhibited an amorphous-like or disordered structure, which resulted in rrP3ATs possessing high electrical properties, such as conductivity and hole mobility. 14 The placement, length, and topology of the side chain are also crucial factors for the ordering structure [15][16][17] and the backbone orientation, such as edge-on and face-on, which affect the direction of charge transport. 18 Recently, branched alkyl groups have been widely used as the side chain in semiconducting polymers because they provide better solubility than simple linear alkyl groups.…”

Influence of the alkyl substitution position on photovoltaic properties of 2D-BDT-based conjugated polymers

“…Besides the extensive studies on design of new backbone structures, side chain engineering is emerging as an important strategy to optimize the structure of photovoltaic polymers [32][33][34]. Generally, researchers focus on the length (namely, carbon atom number) and type (straight or branched) of alkyl chains, which all affect the performance of the photovoltaic polymers.…”

Effects of alkyl chain positioning on conjugated polymer microstructure and field-effect mobilities

“…Synthetically the reduction in solubility can be minimised or even prevented by flanking the fused ring system with solubilising alkyl side chains. 6,7 Unfortunately there is no universal approach applicable to every collinear monomer, but rather the side chain has to be judiciously chosen depending on the desired property. Even though the side-chains have only a minimal effect on the overall electronic properties of a conjugated polymer, they play a key role in defining the solid state properties and material processability.…”