9,9′-Spirobifluorene and 4-phenyl-9,9′-spirobifluorene: pure hydrocarbon small molecules as hosts for efficient green and blue PhOLEDs

We report herein a new pure hydrocarbon material, 4-phenyl-9,9'-spirobifluorene (4-Ph-SBF), with a high triplet energy level (E-T: 2.77 eV) as a host for blue phosphorescent organic light-emitting diodes (PhOLEDs). Structural, thermal, electrochemical and photophysical properties have been investigated in detail and compared to its constituting building block 9,9'-spirobifluorene (SBF) in order to precisely study the influence of the incorporation of a phenyl unit in C4. A surprising out of plane deformation of the fluorene ring and a highly twisted structure have been notably found for 4-Ph-SBF due to the substitution in C4. As both 4-Ph-SBF and SBF possess a high triplet energy level (2.77/2.87 eV resp.), they have been successfully used as host materials for green and blue PhOLEDs. The performance of blue PhOLEDs, ca. 20 cd A(-1), appears to be among the highest reported for pure hydrocarbon derivatives.