Rational Molecular Design for Boosting Afterglow Efficiency in Nonplanar Carbazolocarbazoles

Carbazolocarbazole (CCz) represents a novel class of heterocycles in the carbazole family, distinguished by its unique structure and related properties. However, the significant challenges associated with its synthesis have constrained the exploration and related studies in recent years. Herein, we presented a thorough and reproducible method for synthesizing gram-sized helical CCz, extending its functionalization to investigate both the pristine CCz and its six derivatives with various substituents. This work is the debut of CCz compounds displaying afterglow characteristics in the solid state. The CCz derivatives demonstrated impressive ultralong room-temperature phosphorescence (URTP) lifetimes, ranging from 0.52 to 0.72 s, which are considered relatively long among the carbazole family. The URTP of the CCz series occurs due to the efficient intersystem crossing (ISC) process from the singlet to the triplet-excited states, facilitated by the enhanced spin-orbit coupling (SOC). Based on the comprehensive investigation of seven CCz compounds, we proposed a strategy for elevating the photoluminescence quantum yield (PLQY) of organic URTP emitters. Notably, the most rigid CCz derivatives, SpiroCCz, exhibited the highest total PLQY of 79.9%, one of the highest carbazole-based afterglow emitters in a polymer matrix. Overall, helical CCz derivatives are innovative and promising candidates for afterglow applications in optoelectronic devices, bioimaging, and security printing.