Kinked Star-Shaped Fluorene/Triazatruxene Co-oligomer Hybrids with Enhanced Functional Properties for High-Performance, Solution-Processed, Blue Organic Light-Emitting Diodes

A novel series of kinked star-shaped oligofluorene/triazatruxene hybrids are conveniently prepared via a powerful microwave-enhanced multiple coupling methodology. Constructing kinked star-shaped architectures can effectively suppress crystallization and aggregation. The resulting materials are highly amorphous, showing stable amorphous morphology against crystallization. A triazatruxene core endows the materials with elevated highest occupied molecular orbital (HOMO) levels that are well matched to the anode work function, leading to a significantly improved hole-injection property. They hybrids are highly luminescent in both solution (quantum yield is 0.52-0.80) and the solid-state (quantum yield is 0.45-4.76) with bright blue emission. Remarkably, solution-processed devices displaying single-layer electroluminescence (EL) based on these oligomers exhibit efficient blue EL and demonstrate striking color stability, almost unchanged with increasing driving voltage. The best device performance has a rather low turn-on voltage (3.3 V) and a high device efficiency (2.16% @ 2382 cd m^-2) as well as a high brightness (7714 cd m^-2 @ 10 V) with CIE coordinates of (0.16, 0.15); it shows remarkably better EL performance than devices based on linear oligofluorene or polyfiuorene counterparts. The results prove that an oligomer with kinked star-shaped architecture is extremely promising for efficient and stable blue EL The reasons for the enhanced functional properties and the improved color stability are discussed in relation to the chemical structures and components.