Organoboron functionalized conjugated polymers: synthesis, characterization and anion binding study

Abstract

Thiophene- and fluorene-based polymers represent two important classes of semiconducting materials and their applications in organic light emitting devices, photovoltaics, organic field-effect transistors and chemical sensors have been extensively investigated. Electron-deficient organoboranes provide interesting characteristics including their ability to act as efficient emitters and charge transport materials in optoelectronic devices and as sensory element for nucleophiles. It is desirable to bring together these two classes of building blocks within one system to form a variety of materials with advantageous properties. We have explored two alternative design principles: (i) the embedding of boron into the conjugated polymer main chain and (ii) the direct attachment of boron as a side group to the conjugated polymer backbone. Three different projects were pursued in this general area: 1. The reactive polymer scaffold poly(fluorenylene(bromo)borane) (PFBBr) with alternating fluorene and borane moieties was prepared via B-Sn exchange reaction. Starting from PFBBr as a universal precursor, we obtained a series of polymers for which we can tune the stability, thermal characteristics, and fluorescence behavior by simple post-polymerization modification reactions. By using the same synthetic strategy, we have also prepared a main chain donor--acceptor type polymer based on a combination of fluorene and triphenylamine. As expected for an ambipolar system, this polymer exhibits a remarkable solvatochromic effect in the emission and can be oxidized and reduced electrochemically at moderate potentials. 2. In an alternative approach, a series of polythiophenes with diarylboryl functional groups attached at the lateral positions have been developed in our group by Anand Sundararaman via a post-polymerization borylation route. The electrical and structural properties of the polymer and the chemical stability can be further tuned by variation of the aryl groups on boron, for which the redox active ferrocenyl and sterically bulky Mes or Tip groups were introduced. To further investigate how the main chain chemical structure influences the optoelectronic properties of this type of polymers, we have prepared a class of bis(dimesitylboryl)bithiophene-based alternating copolymers, involving different aromatic -systems such as fluorene, carbazole and triphenylamine derivatives. 3. Organoboron quinolate chelates are promising as light emitting materials because of their high thermal stability and efficient luminescence. We have prepared two new polymers with both the quinolate ligands and boron centers embedded in the main chain. The polymers were obtained by a simple one-step procedure that involves metal-free boron-induced ether cleavage reactions. All the polymers have been characterized by multinuclear NMR spectroscopy, gel permeation chromatography (GPC) and their thermal behavior has been studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Their photophysical and electrochemical…