From Monodisperse Thienyl‐ and Furylborane Oligomers to Polymers: Modulating the Optical Properties through the Hetarene Ratio

Abstract

The application of our newly developed B-C coupling method by catalytic Si/B exchange is demonstrated for the synthesis of a series of triarylboranes (1), monodisperse thienyl- and furylborane dimers (2) and trimers (9), extended oligomers (3) and polymers (3'), as well as mixed (oligo)thienyl-/furylboranes. The structures of 1 aa , 1 bb , and 2 bbb , determined by X-ray crystallography, reveal largely coplanar hetarene rings and BR environments, which are most pronounced in the furylborane species. Photophysical investigations, supported by TD-DFT calculations, revealed pronounced π-electron delocalization over the hetarene backbones including the boron centers. With an extended series of derivatives of varying chain lengths available, we were able to determine the effective conjugation lengths (ECL) of poly(thienylborane)s and poly(furylborane)s, which have been reached with the highest-molecular-weight derivatives of our study. Through variation of the furan-to-thiophene ratio, the photophysical properties of these materials are effectively modulated. Significantly, higher furan contents lead to considerably increased fluorescence intensities. Compounds 1 aa , 1 bb , and 3 a showed the ability to bind fluoride anions. The binding process is signaled by a distinct change in their optical absorption characteristics, thus rendering these materials attractive targets for sensory applications.

Functional Polymeric Materials Based on Main‐Group Elements

“…[123] Donor-acceptor polymers are accessible as well, [124] and the photophysical properties and the Lewis acid strength of these polymers can be tuned by variations in the pendent aryl groups on boron. [125] Using arylsilane precursors,they developed versatile routes for the synthesis of polymers 60 with alternating boron and thiophene or furan moieties (Scheme 7b). In this regard it would be desirable to utilize organosilicon in place of organotin precursors,but the rates for Si/B are generally far lower than for Sn/B exchange reactions.…”

Doping the Backbone of π‐Conjugated Polymers with Tricoordinate Boron: Synthetic Strategies and Emerging Applications

“…With series of derivatives of varying chain lengths at hand, the effective conjugation lengths (ECL) of poly(thienylborane)s and poly(furylborane)s could be determined . This gave n ECL =9 for both cases, according to π–π* absorption wavelength maxima for the infinite chains of 414 and 412 nm, respectively.…”

“…An outstanding feature of the furylborane species is their exceptionally intense blue luminescence, with quantum yields of up to Φ F =71 %. In oligomers of mixed composition, the photophysical properties are effectively modulated by the ratio of furan to thiophene rings incorporated …”

“…Helten and co-workers recently developed an ew method that circumventst his issue. [24] Their method uses less toxic organosilicon compounds instead. Silicon/boron exchange reactions generally proceed at significantly lower rates than analogous Sn/B exchange processes, especiallyi ft he borane involvedf eatures already one BÀCb ond.…”

Funktionelle polymere Materialien auf der Basis von Hauptgruppen‐Elementen

“…[123] Auch Donor-Akzeptor-Polymere sind zugänglich. [125] Unter Verwendung von Arylsilan-Vorstufen entwickelten sie vielseitige Routen fürd ie Synthese von Polymeren 60 mit alternierenden Bor-u nd Thiophenoder Furan-Einheiten (Scheme 7b). Ein Nachteil dieses Verfahrens ist die hohe Toxizitätv on Organozinnhalogeniden, die bei der Polymerisation als Nebenprodukte entstehen.…”