“…1 By tailoring the nature of the substituents and their substitution patterns about the 9,9′-spirobifluorene unit, for example, with an identical or different biphenyl branch, 2,3 it is easy to manipulate the electronic structure, emission spectrum, thermal/ morphological stability, or charge carrier mobility of 9,9′spirobifluorene-based materials. Moreover, with developing emitters equipped with an appropriate electron donor (D) that facilitates hole injection and/or transport and an electron acceptor (A) that improves electron injection and/or transport, 4 it is promising to balance the electron-hole recombination efficiency, to control the levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) as well as the emission color to a fine degree, [5][6][7][8] making such systems increasingly attractive for use in singlelayer OLEDs. [9][10][11] However, the 9,9′-spirobifluorene derivatives featuring donors on one biphenyl branch spiro-linked to another biphenyl moiety bearing acceptors exhibit low photoluminescence efficiencies as a result of strong photoinduced electron transfer.…”