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Abstract A series of tetraarylsilane compounds, namely p ‐BISiTPA ( 1 ), m ‐BISiTPA ( 2 ), p ‐OXDSiTPA ( 3 ), m ‐OXDSiTPA ( 4 ), are designed and synthesized by incorporating electron‐donating arylamine and electron‐accepting benzimidazole or oxadiazole into one molecule via a silicon‐bridge linkage mode. Their thermal, photophysical and electrochemical properties can be finely tuned through the different groups and linking topologies. The para ‐disposition compounds 1 and 3 display higher glass transition temperatures, slightly lower HOMO levels and triplet energies than their meta ‐disposition isomers 2 and 4 , respectively. The silicon‐interrupted conjugation of the electron‐donating and electron‐accepting segments gives these materials the following advantages: i) relative high triplet energies in the range of 2.69–2.73 eV; ii) HOMO/LUMO levels of the compounds mainly depend on the electron‐donating and electron‐accepting groups, respectively; iii) bipolar transporting feature as indicated by hole‐only and electron‐only devices. These advantages make these materials ideal universal hosts for multicolor phosphorescent OLEDs. 1 and 3 have been demonstrated as universal hosts for blue, green, orange and white electrophosphorescence, exhibiting high efficiencies and low efficiency roll‐off. For example, the devices hosted by 1 achieve maximum external quantum efficiencies of 16.1% for blue, 22.7% for green, 20.5% for orange, and 19.1% for white electrophosphorescence. Furthermore, the external quantum efficiencies are still as high as 14.2% for blue, 22.4% for green, 18.9% for orange, and 17.4% for white electrophosphorescence at a high luminance of 1000 cd m −2 . The two‐color, all‐phosphor white device hosted by 3 acquires a maximum current efficiency of 51.4 cd A −1 , and a maximum power efficiency of 51.9 lm W −1 . These values are among the highest for single emitting layer white PhOLEDs reported till now.
Gong et al. (Thu,) studied this question.