High quantum efficiencies of above 30% in blue phosphorescent organic light emitting diodes are achieved by using novel pyridoindole-based bipolar host materials. A high quantum efficiency of 30.0% is obtained at 100 cd/m(2) by using the new host materials.

Transistors On page 5875, J. H. Cho and co-workers demonstrate a new device architecture for flexible vertical Schottky barrier (SB) transistors and logic gates based on graphene-organic-semiconductor-metal heterostructures and ion gel gate dielectrics. The devices show well-behaved p-and n-type characteristics under low-voltage operation (<1 V), yielding high current densities (>100 mA cm-2) and on-off current ratios (>10 3). Biosensors On page 6034, P. K. Wong and co-workers demonstrate a nanorod-based biosensor for dynamic single-cell analysis in native tissue microenvironments. The biosensor is capable of monitoring spatiotemporal mRNA expression in primary human cells, capillary networks, and animal tissues, including the skin, retina, and cornea, challenged mechanically and biochemically. Conjugated Polymers M. Xue and co-workers describe an in situ polymerization method for yielding single-crystal-conjugated polymer (SCCP) arrays on page 5923. As-fabricated SCCP micro-arrays exhibit a smooth surface, excellent environmental stability, and enhanced electron sensitivity, which may bring high performances for CP-based devices, such as supercapacitors, organic solar cells, polymer super-conductors, organic field-effect transistors (OFETs), organic light-emitting diodes (OLEDs), or some flexible electronics. Photocatalysts Well-designed hetero-nanostructural plasmonic photo-catalysts with a multichannel sensitization effect on the charge-carrier dynamics process are developed by B. Dong and co-workers, as described on page 5906. The rational combination of the semiconductor hetero-junction effect and a surface plasmon resonance (SPR) coupling effect of the plasmonic dimers, as well as the nanostructural property of electrospun nanofibers, results in a remarkable enhancement in the efficiency of sol ar to fuels conversion. Carbazole-and triazine-derived thermally activated delayed fl uorescent (TADF) emitters , with three donor units and an even distribution of the highest occupied molecular orbital, achieve high external quantum effi ciencies of above 25% in blue and green TADF devices.

Highly efficient green thermally activated delayed fluorescent organic light-emitting diodes with an external quantum efficiency of 31.2% were investigated by using 3-(3-(carbazole-9-yl)phenyl) pyrido[3',2':4,5]furo[2,3-b]pyridine (3CzPFP) derived from carbazole and pyrido[3',2':4,5]furo[2,3-b]pyridine. The host material showed well-matched photoluminescence emission with absorption of the green dopant material, (4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) and harvested all excitons of 4CzIPN. The 3CzPFP:4CzIPN film exhibited high photoluminescence quantum yield of 100%, and the green delayed fluorescence device employing the 3CzPFP host showed high maximum quantum efficiency of 31.2 ± 0.5% at 1% doping after optimization of the device structure.

Highly efficient thermally activated delayed fluorescent (TADF) emitters, 5-(2-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-5H-benzofuro[3,2-c]carbazole (oBFCzTrz), 5-(3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-5H-benzofuro[3,2-c]carbazole (mBFCzTrz), and 5-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-5H-benzofuro[3,2-c]carbazole (pBFCzTrz), were synthesized to study the effects of ortho-, meta-, and para- linkages between donor and acceptor moieties. oBFCzTrz having ortho- linked donor and acceptor moieties showed smaller singlet-triplet energy gap, shorter excited state lifetime, and higher photoluminescence quantum yield than mBFCzTrz and pBFCzTrz which are interconnected by meta- and para- positions. The TADF device using oBFCzTrz as a blue emitter exhibited high external quantum efficiency over 20%, little efficiency roll-off, and long device lifetime.

Benzofurocarbazole and benzothienocarbazole were used as electron donors of thermally activated delayed fluorescence (TADF) emitters and the performances of the TADF devices were examined. The benzofurocarbazole and benzothienocarbazole donor moieties were better than carbazole as the electron donors of the TADF emitters.

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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.

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