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Helten Group

π-Conjugated Inorganic—Organic Hybrid Polymers

Research

π-Conjugated Inorganic—Organic Hybrid Polymers

π-Conjugated polymers with semiconducting properties have attracted considerable attention owing to their use as cost-effective, lightweight materials for applications in electronic and optoelectronic devices such as organic light-emitting diodes (OLEDs/PLEDs), organic field-effect transistors (OFETs), and organic photovoltaic cells (OPV), or as sensory or imaging materials. Recent advances have shown that the incorporation of inorganic elements into conjugated polymers leads to novel hybrid materials with intriguing properties and functions that cannot be achieved with purely organic compounds.
Particularly, the main chain functionalization with boron atoms opens up new possibilities. Extension of the π-conjugation via the vacant p orbital on boron results in the formation of strongly electron-accepting materials which can be reductively doped, thus yielding favorable electron-transport (n-channel semiconducting) abilities. Such species are often highly photo- and/or electroluminescent, and the Lewis acidity of trivalent boron additionally offers the opportunity to generate polymeric sensors for the specific recognition of physiologically relevant anions (e. g. fluoride, cyanide) or amines.

Poly(p-phenylene iminoborane): A Boron—Nitrogen Analogue of Poly(p-phenylene vinylene) (PPV)

T. Lorenz, M. Crumbach, T. Eckert, A. Lik, H. Helten,* Angew. Chem. Int. Ed. 201756, 2780—2784 [DOI]Angew. Chem. 2017129, 2824—2828 [DOI] ("Hot Paper").

Highlighted in: "Iminoborane units add inorganic flavor to polymers", S. K. Ritter, Chem. Eng. News 201795(8), 11 [DOI].

A BN analogue of the well-known semiconducting organic polymer poly(p-phenylene vinylene) (PPV) has been synthesized via a facile Si/B exchange polycondensation approach. The novel inorganic—organic hybrid polymer and monodisperse oligomers of this type show π-conjugation across the B=N units along the backbone and extension of the conjugation path with increasing chain length.

Dehydrocoupling and Silazane Cleavage Routes to Organic—Inorganic Hybrid Polymers with NBN Units in the Main Chain

T. Lorenz, A. Lik, F. A. Plamper, H. Helten, Angew. Chem. Int. Ed. 201655, 7236—7241 [DOI]Angew. Chem. 2016128, 7352—7357 [DOI].

Highlighted in: "A New Route to Polymers with NBN Backbone", T. M. Swager, Q. Zhang, Synfacts 201612, 0691 [DOI].

Highlighted in: "Trendbericht Makromolekulare Chemie 2016", M. Sommer, F. Wurm, Nachr. Chem. 201765, 348—358 [DOI].

Polymerization through B—N bond formation provided facile access to the first derivatives of a new class of inorganic—organic hybrid polymers having diaminoborane functional groups incorporated into a conjugated polymer backbone. The new materials can be crosslinked via ZrIV centers, thus, demonstrating their applicability as macromolecular poly-ligand systems.

Catalytic B—C Coupling by Si/B Exchange: A Versatile Route to π-Conjugated Organo-borane Molecules, Oligomers, and Polymers

A. Lik, L. Fritze, L. Müller, H. Helten, J. Am. Chem. Soc. 2017139, 5692—5695 [DOI].

Using a novel, highly efficient and environmentally benign B—C bond formation method based on a catalytic Si/B exchange reaction, we have prepared a series of arylborane molecules, oligomers, and polymers. Significantly, this method offers the possibility to apply AB type polycondensations for the synthesis of conjugated organoborane polymers via B—­­­C coupling for the first time. Photophysical investigations, supported by TD-DFT calculations, reveal highly effective π-conjugation in thienyl- and furylborane species; the latter also being highly emissive.

A. Lik, S. Jenthra, L. Fritze, L. Müller, K.-N. Truong, H. Helten, Chem. Eur. J. 2018accepted [DOI] ("Very Important Paper").

Through variation of the furan-to-thiophene ratio, the photophysical properties of these materials are effectively modulated. They are furthermore attractive targets for chemical sensory applications. Binding of fluoride anions is effectively signaled by an optical response.