<i>Endo</i> ‐Encapsulated Multi‐Resonance Dendrimers with Through‐Space Interactions for Efficient Narrowband Blue‐Emitting Solution‐Processed OLEDs

Abstract Different from conventional luminescent dendrimers with fluorophore tethered outside to dendron, here we first developed endo ‐encapsulated luminescent dendrimers with multi‐resonance (MR) fluorophore embedded inside of carbazole dendrons by growing dendrons through 1,8‐positions of central carbazole moiety to create a cavity for accommodating the fluorophore. This endo ‐encapsulated structure not only shields the fluorophore to fully resist aggregation‐caused spectral broadening, but also induce through‐space interactions between dendron and fluorophore via intramolecular π‐stacking, giving lowered singlet state energy and reduced singlet‐triplet energy splitting to accelerate reverse intersystem crossing (RISC) from triplet to singlet states. The resultant dendrimer containing 1,8‐linked second‐generation carbazole dendrons and boron, sulfur‐doped polycyclic MR fluorophore exhibits narrowband blue emission at 471 nm with FWHM kept at 34 nm even in neat film, together with ~4 times enhancement of RISC rate constant compared to its exo‐ tethered counterpart. Solution‐processed OLEDs based on the endo ‐encapsulated dendrimer reveal efficient narrowband blue emissions with maximum external quantum efficiency of 22.6 %, representing the best device efficiency for blue‐emitting multi‐resonance dendrimers so far.