3‐(9‐Carbazolyl)carbazoles and 3,6‐Di(9‐carbazolyl)carbazoles as Effective Host Materials for Efficient Blue Organic Electrophosphorescence

Abstract

Linking topology in oligocarbazoles (see figure) has a strong influence on their electronic properties. 3(6),9′‐linked oligocarbazoles exhibit unusual suppression of electronic coupling between units, leading to localized excited states and very small reduction of triplet energies (compared to the monomer). Coupled with their excellent morphological stability, this makes them suitable as host materials for blue electrophosphorescence devices.

A Highly Efficient Universal Bipolar Host for Blue, Green, and Red Phosphorescent OLEDs

“…[14][15][16][17][18][19][20] However, high driving voltages were often observed for the devices due to its low electron drift mobility. [11,12] Other disadvantages are the low T g (62 8C) [13] leading to easy crystallization, especially when the dopant concentration is low [14,15] and its low triplet energy E T of 2.56 eV even too low for sky-blue phosphor, iridium(III) bis(4,6-(difluorophenyl)-pyridinato-N,C2 0 )picolinate (FIrpic). [16] To increase the glass-transition temperature, triplet energy, and the electron transporting ability of CBP, we proposed to modify CBP by inserting a phosphine oxide moiety PhPO, known to be a point of saturation and an electron-withdrawing group, into the middle of the structure.…”

Salen-Aluminum Complexes as Host Materials for Red Phosphorescent Organic Light-Emitting Diodes

“…The formation of H2 has been confirmed by . 22 The high thermal stability of H1 and H2 appears to be originated from both the steric protection of the Al-center by tert-butyl groups and the penta-coordinate bonding nature around the Al center. The higher T d and T g values of dimeric H2 than those of H1 and other monomeric salen-Al complexes 16 is in accordance with the steric bulkiness of H2 that can restrict molecular motion.…”

Theoretical investigation of the degradation mechanisms in host and guest molecules used in OLED active layers

“…Typically hole-transporting fragments based on carbazole 13,36 or silane 37,38 derivatives have been considered although issues related to device efficiency or lowering of device operating voltage remain. For example, the most commonly used carbazole-based material, 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP) with high triplet energy gaps and excellent hole transporting properties, has been widely used as host material for green and red phosphorescent emitters.…”

“…Depending on the nature of the cyclometalating and ancillary ligands, the relative energies of these states can vary considerably, resulting in different stabilities and device lifetimes. As the phosphorescent materials are distributed within an appropriate organic semi-conductive host matrix to avoid selfquenching of phosphors, [13][14][15] stability of the matrix molecules is also required. Previous attempts at understanding the lifetime of the host materials have focused on requiring a high-glass transition temperature (T g ), electrochemical stability, and morphological stability.…”