| abstract |
The present invention relates to organic electroluminescent materials and devices. Disclosed is a compound having a metal coordination complex structure, the compound having at least two ligands coordinated to the metal; wherein the compound has a a first substituent R 1 ; wherein the first distance is defined as the distance between the metal and one of the atoms in R 1 that is the furthest from the metal among the atoms in R 1 ; wherein said first distance is also longer than any other atom-to-metal distance between said metal and any other atom in said compound; and wherein when defining a sphere with radius r, its center is at said metal and said When the radius r is the smallest radius such that the sphere can enclose all atoms in the compound that are not part of R, the first distance is longer than the radius r by at least |