Tri-, tetra- and pentamers of 9,9'-spirobifluorenes through full ortho-linkage: high triplet-energy pure hydrocarbon host for blue phosphorescent emitter.

4,4'-Dibromo-9,9'-spirobifluorene was first synthesized, and from this intermediate, three fully ortho-linked tri-, tetra-, and pentamers of 9,9'-spirobifluorenes were constructed. The full ortho-linkage impedes the π conjugation of fluorene units, and guarantees their high triplet energies (E(T) = 2.80 eV). A device with the trimer as the first pure hydrocarbon host material for blue phosphor FIrpic shows a maximum current efficiency of 25 cd/A.