Indoloquinoxaline as a terminal building block for the construction of π-conjugated small molecules relevant to organic electronics

•Introduction of a new indoloquinoxaline organic π-conjugated building block.•Simple synthesis of functionalized indoloquinoxaline building blocks.•Synthesis of three new chromophores with progressively red-shifted band gaps.

Herein we introduce the π-conjugated organic building block, 8-bromo-indolo[2,3-b]quinoxaline (indoloquinoxaline, IQ), that combines both electron withdrawing and donating nitrogen atoms. It is accessible from low-cost starting materials through a straightforward and high yielding condensation reaction. In terms of materials design, indoloquinoxaline is suitable for use as a terminal unit; it can act as a planar extension of the π-conjugated system and is easily functionalized with aliphatic side-chains, which can alter material solubility and self-assembly processes. The indoloquinoxaline framework is highly versatile and can be readily derivatized considering the hundreds of commercially available indole and phenylenediamine starting materials. In this case, the indoloquinoxaline building block is neither strongly electron rich or deficient which allows for material optoelectronic properties to be largely dictated by the character of the molecular core, as shown through the incorporation of three different core units, a weak thiophene donor, a strong benzodithiophene donor and an isoindigo acceptor.

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