Si Hyun Han

Unconventional Molecular Design Approach of High-Efficiency Deep Blue Thermally Activated Delayed Fluorescent Emitters Using Indolocarbazole as an Acceptor

Unconventional blue thermally activated delayed fluorescent emitters having electron-donating type indolocarbazole as an acceptor were developed by attaching carbazolylcarbazole or acridine donors to the indolocarbazole acceptor. Three compounds were derived from the indolocarbazole acceptor. The indolocarbazole-acridine combined products showed efficient delayed fluorescent behavior and a high quantum efficiency of 19.5% with a color coordinate of (0.15, 0.16) when they were evaluated as thermally activated delayed fluorescent emitters in deep blue fluorescent devices. This is the first demonstration of the use of electron-donating carbazole-derived moieties as efficient acceptor units of blue thermally activated delayed fluorescent emitters.

Selective F or Br Functionalization of Dibenzofuran for Application as Host Materials of Phosphorescent Organic Light‐Emitting Diodes

Four dibenzofuran-type host materials substituted with a carbazolylcarbazole moiety were synthesized to investigate the effect of substitution position on the material parameters and device performances of host materials. The carbazolylcarbazole moiety was substituted at the 1-, 2-, 3-, and 4-positions of dibenzofuran by F or Br for a comprehensive study of the positional effect of dibenzofuran-derived host materials. Systematic synthesis and comparison of the four host materials revealed that 1-, 2-, and 4-position modification was better than 3-position modification for high triplet energy and high external quantum efficiency.

Deep blue thermally activated delayed fluorescent emitters using CN-modified indolocarbazole as an acceptor and carbazole-derived donors

Deep blue thermally activated delayed fluorescent (TADF) emitters having carbazole derivatives as donors and CN-modified indolocarbazole as an acceptor were developed. Indolocarbazole moiety modified by CN was an acceptor of all the carbazole-based TADF emitters, and carbazole and t-butylcarbazole were donors combined with the CN-modified indolocarbazole. The carbazole-based TADF emitters showed a narrow emission spectrum with a less than 60 nm full width at half maximum, deep blue emission color with a y color coordinate below 0.13, and a high external quantum efficiency of 16.0%.

Rational molecular design overcoming the long delayed fluorescence lifetime and serious efficiency roll-off in blue thermally activated delayed fluorescent devices

Blue thermally activated delayed fluorescent (TADF) devices with short excited-state lifetime, high reverse intersystem crossing rate, and low-efficiency roll-off were developed by managing the molecular structure of donor-acceptor-type blue emitters. Three isomers of blue TADF emitters with a diphenyltriazine acceptor and three carbazole donors were synthesized. The position of the donor moieties in the phenyl linker connecting the donor and acceptor moieties was controlled to devise compounds with a short delayed fluorescence lifetime. A blue TADF emitter with three carbazole donors at 2-, 3-, and 4- positions of a phenyl linker shortened the excited state lifetime to 4.1u2005μs, showed a high external quantum efficiency of 20.4u2009%, and low efficiency roll-off of less than 10u2009% at 1000u2005cdu2009m-2 . Therefore, a molecular design distorting the donors by aligning them in a consecutive way is useful to resolve the issues of long delayed fluorescence lifetime and efficiency roll-off of blue TADF devices.