Strategy Toward Tuning Emission of Star-Shaped Tetraphenylethene-Substituted Truxenes for Sky-Blue and Greenish-White Organic Light-Emitting Diodes

Star-shaped, C3-symmetric, tetraphenylethene (TPE) and 2,3,3-triphenylacrylonitrile (TPAN)-substituted truxenes 7, 8, and 9 were designed and synthesized by the palladium-catalyzed Suzuki and Sonogashira cross-coupling reactions. The TPE-substituted truxenes 7 and 8 show aggregation-induced emission behavior, whereas TPAN-substituted truxene 9 shows aggregation-caused quenching effect in tetrahydrofuran/water medium due to the π–π stacking. The computational calculation on truxenes 7–9 was performed, which reveals that in truxene 9, the electron density transfers from truxene to TPAN. The truxenes 7–9 showed high thermal stability as the 10% weight loss temperature is more than 400 °C. The ionization potentials close to 6.0 eV were estimated for the solid samples of truxenes 7–9 by photoelectron emission spectrometry. Solid samples of the studied truxenes exhibited strong emission with high quantum yields (up to 47%). Electroluminescent properties of truxene derivatives 7–9 were investigated in solution-processed and vacuum-deposited organic light-emitting diodes (OLEDs). Greenish-white nondoped OLEDs with maximum brightness of 7000 cd/m2 and maximum external quantum efficiency of 3.8% were fabricated using truxene-cored compound 7 as the fluorescent emitter.