Low molecular organic glasses for blue electroluminescence

Spiro-linkage is used to modify the steric demand of low molecular organic compounds to improve their processability and morphologic stability, while their electronic properties are retained. These spiro-linked compounds form stable nonpolymeric organic glasses with high glass transition temperatures, usually associated with amorphous polymers. High quality amorphous films with high morphologic stability can be prepared with these spiro-linked luminescent or charge transport materials by conventional spin-coating techniques as well as by vapor deposition. Based on these spiro-compounds, blue electroluminescence devices with high color purity, high brightness and low turn-on voltage are presented. A blue light-emitting two-layer device, fabricated by combining a hole transporting spiro-TAD with an electron transporting spiro-PBD, shows a turn-on voltage at 2.7 V and a luminance of 500 cd/m2 at 5 V.