Strategic Synchronization of 7,7-Dimethyl-5,7-dihydroindeno[2,1-b]carbazole for Narrow-Band, Pure Violet Organic Light-Emitting Diodes with an Efficiency of > 5% and a CIE y Coordinate of < 0.03

A novel violet emitter, 1,3-bis[10,10-dimethyl-10 H -indeno[2,1- b ]]indolo[3,2,1- jk ]indolo[1′,2′,3′:1,7]indolo[3,2- b ]carbazole ( m -FLDID ), was designed and synthesized by meta -oriented bis -fusion of two 7,7-dimethyl-5,7-dihydroindeno[2,1- b ]carbazole ( DMID ) subunits for use in a pure violet organic light-emitting diode (OLED). Incorporation of the DMID subunits effectively reduced the nonradiative recombination rate, improving the photoluminescence quantum yield of the m -FLDID emitter. The meta -oriented bis -fusion of the two DMID subunits not only triggered an alternative distribution of the frontier orbitals but also effectively locked the π-conjugation chain, which ultimately resulted in a narrow-band, pure violet emission of the m -FLDID emitter. Doped m -FLDID devices possessed an external quantum efficiency (EQE) of > 5%, pure violet emission with a maximum at 407 nm, a narrow full width at half-maximum of 17 nm, and a Commission Internationale de l’éclairage y coordinate of less than 0.03. This is the first work reporting an EQE of > 5% and an extremely narrow emission spectrum for a pure violet emitter.