Endo-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.