Glaser-Hay-Coupled Random Copolymers Containing Boron Difluoride Formazanate Dyes

Abstract

𝜋-Conjugated polymers, including those based on acetylenic repeating units, are an exciting class of materials that offer narrow optical band gaps and tunable frontier orbital energies that lead to their use in organic electronics. This work expands the knowledge of structure-property relationships of acetylenic polymers through the synthesis and characterization of a series of Glaser-Hay-coupled model compounds and random copolymers comprised of BF₂ formazanate, fluorene, and/or bis(alkoxy)benzene units. The model compounds and copolymers synthesized exhibit redox activity associated with the reversible reduction of the BF₂ formazanate units and the irreversible reduction of the fluorene and bis(alkoxy)benzene units. The copolymers exhibit absorption profiles characteristic or intermediate of their respective models and homopolymers, leading to broad absorption of UV-vis light. The alkyne linkages of the model compounds and copolymers are reacted with [Co₂(CO)₈] to convert the alkyne functional groups into cobalt carbonyl clusters. This transformation leads to blue-shifted absorption profiles due to a decrease in π-conjugation, demonstrating the ability to tune the properties of these materials through post-polymerization functionalization. The redox activity and broad absorption bands of the polymers reported make them excellent candidates for use in photovoltaics and other light-harvesting applications.

Keywords: BF2 formazanate dyes; Glaser‐Hay Coupling; UV–vis spectroscopy; alkynes; cyclic voltammetry.

Figure 1

Examples of Glaser‐ and Glaser‐Hay‐coupled polymers and the monomers used for copolymerization in this work.

Figure 2

Examples of π‐conjugated systems incorporating BF₂ formazanate dyes.

Scheme 1

Synthesis of model compounds, Ph‐BF₂‐Ph, Ph‐FL‐Ph, Ph‐Bn‐Ph, and BF₂‐BF₂‐BF₂ and their cobalt carbonyl derivatives, Ph‐Co‐BF₂‐Co‐Ph, Ph‐Co‐FL‐Co‐Ph, and Ph‐Co‐Bn‐Co‐Ph. Monomers and building blocks are defined within the dashed box.

Figure 3

Solid‐state structures of model compounds Ph‐BF₂‐Ph and Ph‐FL‐Ph. Hydrogen atoms are omitted for clarity and anisotropic displacement parameter ellipsoids are shown at a 50% probability level.

Scheme 2

Synthesis of polymers, P‐FL, P‐Bn, P‐BF₂‐FL, P‐BF₂‐Bn, and P‐FL‐Bn, and their cobalt carbonyl derivatives, Co‐P‐BF₂‐FL, Co‐P‐BF₂‐Bn, and Co‐P‐FL‐Bn. Monomers and building blocks are defined within the dashed box.

Figure 4

Cyclic voltammograms of a) model compounds and b) polymers as 1 mm, dry, degassed CH₂Cl₂ solutions containing 0.1 m [nBu₄N][PF₆] as the supporting electrolyte, recorded at 500 mV s⁻¹. The initial scan direction is denoted by the arrows.

Figure 5

UV–vis absorption spectra recorded for a) CH₂Cl₂ solutions of model compounds, b) CH₂Cl₂ solutions of cobalt carbonyl derivatives of models, c) 27 µm CH₂Cl₂ solutions of homopolymers and copolymers, and d) CH₂Cl₂ solutions of cobalt carbonyl derivatives of copolymers: Co‐P‐BF₂‐FL (20 µm), Co‐P‐BF₂‐Bn (22 µm), and Co‐P‐FL‐Bn (21 µm).