According to an aspect of the present disclosure, a compound having a metal planar tetradentate coordination configuration is disclosed. In the compounds, the metal M is Pt or Pd; the four coordinating atoms are Z1, Z2, Z3, and Z4 and are each selected from N, C, and O. The compound includes a substituent R, and atoms M, Z1, Z2, Z3, and Z4 are used to define a first plane that passes through the metal M and is positioned to have a minimum sum of shortest distances with Z1, Z2, Z3, and Z4. At least one non-hydrogen atom in R falls within a distal circle of a cylinder extending perpendicular to the first plane, where the distal circle of the cylinder is a height h from the base circle and the height h ranges from 3.3 Å to 4.8 Å.