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

Abstract

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 0.45–0.76) 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 polyfluorene 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.

Blue Single‐Layer Organic Light‐Emitting Diodes Using Fluorescent Materials: A Molecular Design View Point

“…From these results, one may note that with three similar terfluorenyl antennas, the fluorophore with the central triazatruxene leads to higher OLED efficiency than those with the central triphenylamine or carbazole. This order of efficiency is in accordance with the HOMO energy levels of the three compounds −5.27 eV for 41 , [ 62 ] −5.66 eV for 37, [ 61 ] and −5.75 eV for 38 . [ 61 ]…”

“…Changing the cathode from Ba/Al to Ca/Al in SP‐SL 43 b leads to a V on decrease from 5.3 to 3.5 V but also to a decrease of the performance especially CE which is lowered from 2.07 to 1.4 cd A −1 . [ 63 ] Such variation is not the same than that reported above with 41 as EML [ 62 ] (3.3–3.5 V for V on and 1.56–1.7 cd A −1 for CE from SP‐SL 41 a to SP‐SL 41 b).…”

Triazatruxene-containing hyperbranched polymers: Microwave-assisted synthesis and optoelectronic properties

“…Moreover, emission peak at around 440 nm gradually increased with increasing the degree of branching from PTF3 to PTF1, while the emission peak at around 420 nm generally decreased. The PL spectra of PTF1 appeared very similar to those recorded from its corresponding monodisperse three-arm triazatruxene-fluorene cooligomer counterparts C2 or C3 [18]. This illustrated that hyperbranched polymers with higher degree of branching exhibited closer optical behaviors to those of their monodisperse oligomer counterparts.…”

Aromatic S-Heterocycle and Fluorene Derivatives as Solution-Processed Blue Fluorescent Emitters: Structure–Property Relationships for Different Sulfur Oxidation States

“…As shown in Figure , the performance of the D2 device is much better, and the main reason for the improvement is that (1) the D2 device has a significantly lower electron-injection barrier and higher electron mobility due to the stronger electron affinities and (2) D2 has a higher photoluminescence quantum yield in the solid-state film (Table ). To the best of our knowledge, the performance of D1 and D2 devices is among the best undoped deep-blue and blue SP SM single-layer OLEDs, respectively. − In the PTZ system, the devices of P1 and P2 displayed the EQE of 2.1% and 1.2% with CIE coordinates of (0.22, 0.51) and (0.21, 0.19), respectively. The EL spectrum of the device based on P2 was not stable (Figure S9, Supporting Information), which may be due to the intermolecular excimer induced by the aggregation of emissive molecules.…”