A high-efficiency blue multiple resonance emitter with enhanced horizontal emitting dipole orientation based on indolocarbazole

Abstract

Thermally activated delayed fluorescence emitters with multiple resonance effect have drawn much attention very recently for their extremely sharp spectra and nearly unity photoluminescence quantum yields, showing promising potential for application in ultra-high-definition displays and organic light-emitting diodes. Though strategies have been put forward for tuning the emitting color of these molecules, most emitters have been faced with the problem of spectral broadening once the emission is redshifted. Herein, by virtue of the increased short-range charge transfer advantages of 5-phenyl-5,7-dihydroindolo[2,3-b]carbazole, an asymmetrical B, N/O based MR emitter (IDCzBNO) is constructed. Compared with its carbazole containing predecessor, IDCzBNO shows bathochromic-shifted spectra, from deep blue to blue emission without sacrificing color purity. And the emitter exhibited bright blue emission peaking at 458 nm with a full-width-at-half-maximum of 24 nm in solution, as well as a high fluorescence quantum efficiency of 95%. Besides, thanks to its more expanded planar structure, a high horizontal emitting dipole orientation of 83% is obtained in doped films. As a result, the related blue OLED devices employing the triplet–triplet annihilation mechanism exhibited a small FWHM of 28 nm and the maximum external quantum efficiency of 11.5% with negligible efficiency roll-off, manifesting the effectiveness of the red-shifting emission spectra in achieving ideal narrowband blue emitters.