Highly Efficient Phosphorescent Green Organic Light-Emitting Diodes with High Energy Gap Host Materials

A Comparison between Triphenylmethyl and Triphenylsilyl Spirobifluorenyl Hosts: Synthesis, Photophysics and Performance in Phosphorescent Organic Light-Emitting Diodes

“…The high performance of the SB-Si device shows that this material is significantly better at dispersing Ir(ppy) 3 than SB-C . The EQE obtained using SB-Si also agrees with data from previously published OLED devices using Ir-based emitters in the same SB-Si host [ 24 , 25 ].…”

“…The HOMO levels were −6.2 and −6.3 eV for SB-C and SB-Si, respectively, whereas the LUMO levels were −1.3 eV for the SB-C and −1.5 eV for the SB-Si. The HOMO energies are similar to the value reported for SB-Si (−6.2 eV) obtained using photoemission yield spectroscopy [25]. Moreover, the oxidation potential observed for SB-Si (1.34 V) is close to values reported for a series of silicon-substituted dimethylfluorenyl compounds (E ox = 1.4 V) [16].…”

“…SB-Si was synthesized more efficiently, as shown in Scheme 2 . The addition of Ph 3 SiCl to 2-lithio-9,9′-spirobifluorene results in the SB-Si with a yield of 78% as a pure isolated product [ 24 , 25 ].…”

“…Triphenyl-9,9-spirobifluoren-2-yl silane ( SB-Si ) [ 24 , 25 ]. To a solution of 0.78 g (2 mmol) 2-bromo-9,9-spirobifluorene ( 1 ) in dry THF was added 1.38 mL (2.2 mmol) of n-BuLi (1.6 M in hexanes) under an N 2 atmosphere to obtain an orange solution.…”

“…However, due to negligible steric hindrance between the moieties, these hosts have lower triplet energies compared to spirobifluorene (E T = 2.8 eV), and therefore are poor candidates for confining triplet excitons on blue phosphorescent dopants in PHOLEDs. To address this issue, highly twisted spirobifluorenyl dimers and oligomers with an ortho–ortho linkage between spirobifluorenes moieties were introduced by Ma and Poriel et al, [ 21 , 22 , 23 , 24 , 25 ] which inhibited conjugation and retained the high triplet energy of the parent spirofluorene.…”