New dibenzofuran/spirobifluorene hybrids as thermally stable host materials for efficient phosphorescent organic light-emitting diodes with low efficiency roll-off.

A new class of host materials DBFSF (DBFSF2 and DBFSF4) is facilely synthesized through a Suzuki coupling reaction between dibenzofuran and spirobifluorene. Their thermal, electrochemical, electronic absorption and photoluminescent properties are fully investigated. High glass transition temperatures (T(g)) of 115 °C and 124 °C are observed for DBFSF2 and DBFSF4, respectively, due to the introduction of bulky spirobifluorene groups. As expected, the DBFSF4 with a twisted-linkage exhibits higher triplet energy than DBFSF2 and can be used in blue and green phosphorescent OLEDs. Electrophosphorescent devices with DBFSF2 and DBFSF4 as hosts were fabricated. Besides the good current efficiencies of 22.2 cd A(-1) for blue and 64.4 cd A(-1) for green, low efficiency roll-off has also been achieved for both devices.