Diphenyl-bis[4-(pyridin-3-yl)phenyl]silane, DPPS, has two pyridyl groups attached to the tetra-phenylsilane. Hence, it is electron-deficient.
Almost considered as an insulator, DPPS is a weak electron-transporting material with a wide bandgap Eg = 4.0 eV. Due to its deep HOMO energy level, DPPS is also used as a hole-blocking layer material in photo-electronic devices.