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Conventional semiconducting polymer synthesis typically involves transition metal-mediated coupling reactions that link aromatic units with single bonds along the backbone. Rotation around these bonds contributes to conformational and energetic disorder and therefore potentially limits charge delocalisation, whereas the use of transition metals presents difficulties for sustainability and application in biological environments. Here we show that a simple aldol condensation reaction can prepare polymers where double bonds lock-in a rigid backbone conformation, thus eliminating free rotation along the conjugated backbone. This polymerisation route requires neither organometallic monomers nor transition metal catalysts and offers a reliable design strategy to facilitate delocalisation of frontier molecular orbitals, elimination of energetic disorder arising from rotational torsion and allowing closer interchain electronic coupling. These characteristics are desirable for high charge carrier mobilities. Our polymers with a high electron affinity display long wavelength NIR absorption with air stable electron transport in solution processed organic thin film transistors., Semiconducting polymers are usually prepared by transition metal mediated coupling reactions that cause problems for sustainability and biological applications. Here the authors synthesise fused electron deficient polymers that are air stable and have high electron affinities, via metal free aldol polymerisation reactions.

A novel six-step synthesis of rac-5-(hydroxymethyl)-l-(tetrahydro-2'-oxo-fur-3'-yl)-lH-pyrrole-2-carboxaldehyde (rac-1) starting from 2-methylfuran has been developed. The key step is the formation of rac-2-methyl-l-(tetrahydro-2'-oxofur-3'-yl)- lH-pyrrole (rac-7) according to the Clauson-Kaas procedure. Subsequent Vilsmeier formylation, oxidation with lead tetraacetate, and enzymatic hydrolysis led to rac-1.

The present invention relates to polymers comprising one or more (repeating) unit(s) of the formula (I) which are characterized in that Ar1 and Ar1' are independently of each other are an annulated (aromatic) heterocyclic ring system, containing at least one thiophene ring, which may be optionally substituted by one, or more groups, and their use as organic semiconductor in organic devices, especially in organic photovoltaics (solar cells) and photodiodes, or in a device containing a diode and/or an organic field effect transistor. The polymers according to the invention have excellent solubility in organic solvents and excellent film-forming properties. In addition, high efficiency of energy conversion, excellent field-effect mobility, good on/off current ratios and/or excellent stability can be observed, when the polymers according to the invention are used in organic field effect transistors, organic photovoltaics (solar cells) and photodiodes.

The present invention relates to polymers comprising one or more (repeating) unit(s) of the formula A polymer, comprising (repeating) unit(s) of the formula (1) and (2), wherein A is a repeating unit of the formula (I), and -COM1- is a repeating unit of formula (3), or (4), and their use as organic semiconductor in organic devices, especially in organic photovoltaics (solar cells) and photodiodes, or in a device containing a diode and/or an organic field effect transistor. The polymers according to the invention have excellent solubility in organic solvents and excellent film-forming properties. In addition, high efficiency of energy conversion, excellent field-effect mobility, good on/off current ratios and/or excellent stability can be observed, when the polymers according to the invention are used in organic field effect transistors, organic photovoltaics (solar cells) and photodiodes.