Post-synthesis of Lewis acid-base adducts as thermally activated delayed fluorescence radical emitters for color-tunable displays and encryption via inkjet printing

Abstract

Post-synthesis of color-tunable luminescent compounds, from either solid-state mechanical grinding or solution blending, was demonstrated with a triazine-based fluorescent host as Lewis base and a typical Lewis acid tris(pentafluorophenyl)borane (BCF). The nitrogen atoms on the triazine group of the Lewis base provide lone pairs of electrons for binding BCF which resulted in charge transfer emission and radical nature, due to a dramatic reduction of the singlet–triplet energy gap from 0.59 to 0.08 eV. This allows triplet exciton up-conversion via reverse intersystem crossing (RISC) process, proven by a high external quantum efficiency of 6.7% measured from the spin-coated organic light emitting diodes (OLEDs), consisting of the Lewis acid-base adducts. By inkjet printing BCF ink on the seeding layer of the fluorescent Lewis base, we precisely regulated the emission ranging from deep-blue to orange-red.