Synthesis and characterization of oligothiophene-modified spirobifluorene

Abstract

A series of novel 9,9′-spirobifluorenes functionalized by non-substituted oligothiophenes were synthesized through a coupling reaction between the oligothienyl-zinc chloride and the brominated spirobifluorene. The core is a 9,9′-spirobifiuorene and all the branching arms are affixed to the core in a single operation, which makes the syntheses highly convergent. The tetrahedral bonding atom at the center of a spiro-annulated molecule maintains 90° angle between the connected conjugated moieties via a σ-bonded network, which is useful to modify the steric demand of small molecular compounds to improve their processibility and morphologic stability, with their electronic properties maintained. Contrary to the non-substituted α-oligo-thiophenes, which naturally intend to crystallize, the oligothiophene modified 9,9′-spirobifluorenes were found to readily form amorphous glasses at ambient temperature and to exhibit high morphological stability with high glass transition temperatures ranging from 101°C to 186°C. This series of materials also kept the good properties of oligothiophenes, such as the easy accessibility through various synthetic methodologies, good chemical and thermal stability, as well as the tunable energy levels and the emission color.