Boron Doping Modulates Carbazolocarbazoles with Color-Tunable Afterglow and Long-Lived Electroluminescence

Carbazolocarbazole (CCz) frameworks represent a promising
class
of afterglow-active emitters owing to their rigid helical π-systems.
Here, we systematically investigate the effect of boron incorporation
in a series of CCz derivatives (tOCCz, monoboron tBOCCz, and diboron
tDBOCCz). Boron doping induces color-tunable hybrid afterglow combining
thermally activated delayed fluorescence (TADF) and room-temperature
phosphorescence (RTP), with lifetimes exceeding 0.2 s and thermochromic
shifts from green-yellow (300 K) to orange-red (77 K). Remarkably,
an afterglow organic light-emitting diode (OLED) using tBOCCz as a
single dopant achieves a low driving voltage of 2.8 V, record-high
luminance of 22,021 cd m–2, a high external quantum
efficiency of 5.0%, and ultralong electroluminescence (EL) visible
for ∼2 s (lifetime 263 ms). Achieving high efficiency, high
brightness, and extended EL duration together marks a benchmark for
afterglow OLEDs. Overall, boron doping provides a versatile molecular
strategy to realize color-tunable afterglow and durable EL for future
responsive optoelectronics.