Boron-Doped α-Oligo- and Polyfurans: Highly Luminescent Hybrid Materials, Color-Tunable through the Doping Density

Abstract

Doping of π-conjugated polymers or molecular compounds with trivalent boron atoms has recently emerged as a viable strategy to produce new materials with intriguing properties and functions. The combination of boron with furan moieties has been only scarcely explored so far, although the resulting furan-based materials have several notable features, including favorable optoelectronic properties and improved sustainability. Herein, we investigate the doping of α-polyfurans with a varying number of boron atoms. A series of poly­(oligofuran boranes) and oligofuran-bridged bisboranes have been prepared via microwave-assisted Stille-type catalytic cross-coupling protocols. In the solid-state structures of the molecular compounds, the furan and the borane moieties exhibit a strictly coplanar arrangement; the derivative with a pentafuran bridge forms a dimeric structure in the solid state. All new compounds show considerable absorption and emission features in the visible range that arise from π–π* transitions in the oligofurylborane backbone. They are highly luminescent with quantum yields between 89 and 97% for the bisboranes and up to 87% for the difuran-bridged polymer PB2F. Their emission colors can be effectively tuned in the visible range from blue to orange via the length of the oligofuran linker. Spectroelectrochemical investigations on the difuran-bridged bisborane BB2F and polymer PB2F revealed fully reversible stepwise reductions to the respective radical anion (polaron), with absorption features in the near-infrared (NIR) region, and subsequently to a dianion (dipolaron). Overall, the doping of α-oligofurans with boron leads to a decrease of the frontier orbital energies, a reduction of the electronic band gap, and the formation of very robust and oxidatively stable materials.

Synthesis and Structure‐Property Relationships in Regioisomeric Alternating Borane‐Terthiophene Polymers

“…The higher molecular weight sample of PFB3T’‐B showed multiple series of peaks due to one or two additional thiophene units, which still primarily correspond to cyclic products. The formation of cyclic rather than linear conjugated polymers has been reported for Suzuki‐Miyaura polycondensation reactions with suitably shaped (kinked) monomers, [19] but has to our knowledge only rarely been observed [5l,14e,f] in Stille polymerization of thiophenes. In our case, cyclic tetramers and pentamers are obtained preferentially, possibly also aided by the bent shape of the dithienylborane building blocks (Figure 4b).…”

Controlling the aggregation and assembly of boron‐containing molecular and polymeric materials

“…Over the past decades, boron-containing conjugated π-systems have frequently been employed to construct color-tunable π-conjugated polymers. [84][85][86][87] In a different approach, Wang, Li and co-workers demonstrated that multicolor emission that is dependent on the degree of polymerization can be achieved by chromophore assembly of nonconjugated side-chain functionalized polymers PB8 (Figure 3B). [88] They utilized a stimulus-responsive boron chromophore that exhibits different emission colors in its closed (red, tetracoordinate boron) and open conformation (blue, tricoordinate boron).…”

Synthesis and Characterizations of Polythiophene Networks with Nonplanar BN Lewis Pair Building Blocks

“…The boron (B) atom is a special member of the main-group elements. Implanting B atom with an empty p-orbital endowed OCPs with intriguing optoelectronic properties that are distinct from other OCPs. ,− For example, OCPs with a tricoordinate B-center exhibited excellent toxic material (F/CN anions and amines) sensing properties. , Introducing tricoordinate or tetracoordinate B-building blocks with strong electron-withdrawing characteristics into polymeric backbones efficiently lowered the LUMOs of OCPs, consequently enhancing the electron-accepting and electron-transporting characteristics. ,− …”