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

Star-shaped, <i>C</i><sub>3</sub>-symmetric, tetraphenylethene (TPE) and 2,3,3-triphenylacrylonitrile (TPAN)-substituted truxenes <b>7</b>, <b>8</b>, and <b>9</b> were designed and synthesized by the palladium-catalyzed Suzuki and Sonogashira cross-coupling reactions. The TPE-substituted truxenes <b>7</b> and <b>8</b> show aggregation-induced emission behavior, whereas TPAN-substituted truxene <b>9</b> shows aggregation-caused quenching effect in tetrahydrofuran/water medium due to the π–π stacking. The computational calculation on truxenes <b>7–9</b> was performed, which reveals that in truxene <b>9</b>, the electron density transfers from truxene to TPAN. The truxenes <b>7–9</b> 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 <b>7–9</b> 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 <b>7–9</b> were investigated in solution-processed and vacuum-deposited organic light-emitting diodes (OLEDs). Greenish-white nondoped OLEDs with maximum brightness of 7000 cd/m<sup>2</sup> and maximum external quantum efficiency of 3.8% were fabricated using truxene-cored compound <b>7</b> as the fluorescent emitter.