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A phosphine oxide-substituted double spirobifluorene compound with high thermal stability

A high thermal stability spirobifluorene core derivative with a substituted diphenylphosphine oxide moiety was synthesized as a new electron transport material (spiro(cyclopenta[def]fluorene-1,5,9′9″-bifluorene)-2′,2″-diylbis(diphenylphosphineoxide) [DSPPO1]) for phosphorescent organic light-emitting diodes (PHOLEDs). The glass transition temperature of DSPPO1 was observed at 156°C and was higher than that of common electron transport materials. The triplet energy of DSPPO1 was 2.77 eV and DSPPO1 was appropriate as an electron transport material for PHOLEDs. The highest occupied molecular orbital and lowest unoccupied molecular orbital of DSPPO1 were −6.51 and −2.70 eV, respectively. The energy level of DSPPO1 was suitable for hole blocking and electron injection as an electron transport material for PHOLEDs.