Thermally activated delayed fluorescence (TADF) properties of a dicarbazole-triazine compound, 9-(4,6-diphenyl-1,3,5-triazin-2-yl)-9'-phenyl-3,3'-bicarbazole (CzT), and its OLED characteristics were investigated. An estimated small energy gap of about 90 meV between the singlet and triplet energy states of CzT made the up-conversion of triplet excitons back to a singlet state possible. The origin of the observed delayed fluorescence has been shown to be thermally activated delayed fluorescence. An organic light emitting diode (OLED) with CzT as an emitter showed the maximum external quantum efficiency (EQE) of 6%. For comparison, another carbazole-triazine derivative of 3-(2'-(4,6-diphenyl-1,3,5-triazin-2-yl)-[1,1'-biphenyl]-2-yl)-9-phenyl-9H-carbazole (PhCzTAZ) with a similar structure was also studied. PhCzTAZ showed a low fluorescence quantum yield with no TADF.

Non‐precious metal catalysts of the oxygen reduction reaction are highly favored for use in polymer electrolyte fuel cells (PEFC) because of their relatively low cost. Here, a new carbon‐black‐supported pyrolyzed Co‐corrole (py‐Co‐corrole/C) catalyst of the oxygen reduction reaction (ORR) in a PEFC cathode is demonstrated to have high catalytic performance. The py‐Co‐corrole/C at 700 °C exhibits optimized ORR activity and participates in a direct four‐electron reduction pathway for the reduction of O2 to H2O. The H2‐O2 PEFC test of py‐Co‐corrole/C in the cathode reveals a maximum power density of 275 mW cm−2, which yields a higher performance and a lower Co loading than previous studies of Co‐based catalysts for PEFCs. The enhancement of the ORR activity of py‐Co‐corrole/C is attributable to the four‐coordinated Co‐corrole structure and the oxidation state of the central cobalt.

A series of meso-to-meso ethynyl-bridged multiporphyrin arrays have been synthesized using Sonogoshira palladium-catalyzed cross-coupling reactions involving the appropriate ethynylporphyrin and iodoporphyrin precursors. The absorption spectra of these multiporphyrins show splitting of the Soret bands and significant red shifts of the Q bands as compared to the combination of the corresponding components. These conjugated multiporphyrins also show red shifts in their emission spectra as the pi-conjugation is expanded. In the electrochemical measurements, the porphyrins dimer 7 shows two 1 - e- oxidations at E(1/2) = +0.63 and +0.76 V for the first electron abstraction from the two porphyrin rings, indicating electronic communication between the two porphyrin units. The porphyrin trimer 4 exhibits the first and second 1 - e- oxidations at E(1/2) = +0.68 and +0.77 V, respectively, which correspond to the two outer porphyrins. The cyclic voltammogram of pentamer 5 shows two overlapping 1 - e- couples at E(1/2) = +0.56 and +0.66 V, and one 2 - e- couple at E(1/2) = +0.86 V, for the four outer porphyrin units. These results demonstrate that in the porphyrin trimer and pentamer the individual peripheral porphyrin units are electrochemically coupled via a central porphyrin core. The UV-Vis-NIR spectra of the oxidized species of these multiporphyrins exhibit a broad intervalence charge transfer (IVCT) band in the region from 1200 to 3000 nm. The present work shows that a central porphyrin unit appended with ethynyl bridges affords strong electronic interactions between the peripheral porphyrin rings over a distance of about 15 A.

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