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.