Increase the molecular length and donor strength to boost horizontal dipole orientation for high-efficiency OLEDs

Three pyridine-carbonitrile (PPC) fluorophores with amine-type donors, carbazole, tert-butylcarbazole, and spiroacridine have been designed and synthesized. These PPC-based emitters exhibit excellent photoluminescence quantum yields of 92-100%, thermally activated delayed fluorescence (TADF) and thermal stability. More importantly, with increasing molecular lengths via donor modification strategy, it fulfills the aim to rise the horizontal dipole orientation ratios from 76% to 83%. Remarkably, a high-performance green OLED based on spiroacidine-PPC dopant exhibited an external quantum efficiency of 37.2%, a current efficiency of 123.5 cd A(-1) and a power efficiency of 121.3 lm W-1 with a relative low driving voltage, only 2.9 V.