10 research outputs found
Carbazole based polymers as hosts for blue iridium emitters: synthesis, photophysics and high efficiency PLEDs
This article reports the synthesis of new carbazole based polymers and their application as hosts in sky-blue polymer light emitting devices (PLEDs) with a solution-processed emitting layer doped with a cyclometalated Ir(III) complex. We systematically investigate their effect on the PLED performance. A current efficiency of 19.7 cd A(-1) and a brightness of 1850 cd m(-2) were achieved with these polymers. The roll-off in electrophosphorescent quantum efficiency in PLEDs was shown to arise mainly from triplet-triplet annihilation between dopants in the hosts with tert-butyl groups. It has been shown that in the devices with hosts without tert-butyl groups the efficiency roll-off is additionally affected by electric field quenching. In these carbazole based polymers, triplet dimers are formed and tert-butyl groups do not limit the intermolecular interactions to prevent triplet dimer formation, nevertheless tert-butyl groups reduce charge transport
Through-Space 1,4-Palladium Migration and 1,2-Aryl Shift: Direct Access to Dibenzo[a,c]carbazoles through a Triple C¢H Functionalization Cascade
A palladium-catalyzed expeditious synthesis of
dibenzofused carbazoles from readily available 2-arylindoles
and diaryliodonium salts is reported. Interestingly,
after the electrophilic C3 palladation of indole, an unexpected “through-space” 1,4-palladium migration to the 2-
aryl moiety, by remote C¢H bond activation followed by
C¢H arylation with diaryliodonium salt, and an unprecedented
1,2-aryl shift take place. Finally, an intramolecular
cross-dehydrogenative coupling (CDC) at the C2 position
affords dibenzo[a,c]carbazoles in high yields. Remarkably,
the present migratory annulation occurs through three C¢
H bond activation one C¢C bond cleavage, and the simultaneous construction of three new C¢C bonds in a single
operation