SPPO13, 2,7-Bis(diphenylphosphoryl)-9,9'-spirobifluorene, has a structure with an electron donating spirobifluorene core surrounded by two identical electron withdrawing diphenylphosphine oxide groups, while SPPO1 has only one diphenylphosphine oxide group attached to the spirobifluorene.
Due to its electron deficient nature, SPPO13 is used as an n-type solution-processable electron transporting material. SPPO13 could also be used as universal bipolar co-host for blue, green and red phosphors while blending with hole transporting materials such as tris(4-carbazoyl-9-ylphenyl)amine (TCTA).