A compound is disclosed that has a metal coordination complex structure having at least two ligands coordinated to the metal; wherein the compound has a first substituent R1 at one of the ligands' periphery; wherein a first distance is defined as the distance between the metal and one of the atoms in R1 where that atom is the farthest away from the metal among the atoms in R1; wherein the first distance is also longer than any other atom-to-metal distance between the metal and any other atoms in the compound; and wherein when a sphere having a radius r is defined whose center is at the metal and the radius r is the smallest radius that will allow the sphere to enclose all atoms in the compound that are not part of R1, the first distance is longer than the radius r by at least 2.9 Å.