Toward Achieving Single-Molecule White Electroluminescence from Dual Emission of Fluorescence and Phosphorescence

White
organic light-emitting diodes (WOLEDs) are of great value
in daily life. However, the organic white-emissive single molecules
in OLEDs are rare. Herein, we report a group of carbazolyl derivatives
containing thiophene (PhCz-S), selenophene (PhCz-Se), and tellurophene
(PhCz-Te). Through modulating the chalcogen atom, the promoted intersystem
crossing brings room-temperature phosphorescence. Moreover, PhCz-Se
exhibits Commission Internationale de l’Eclairage (CIE) coordinates
of (0.30, 0.29) in OLEDs measured at 4 V, which is the first example
of the single-molecule WOLEDs combined with dual emission from singlet
and triplet states. Also, PhCz-Te realized WOLEDs in a single emission
layer at CIE coordinates of (0.34, 0.33). The theoretical and experimental
results clearly show that the adjustment of heavy atoms exerts influence
on the luminescent properties, which provides a new strategy for designing
single-molecule WOLEDs.