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A new zinc-based annulation method produced regioselectively a variety of 2,3,6,7-tetraarylbenzo1,2- b:4,5- b ‘difurans in good yields. The organic electroluminescent devices using these tetraarylbenzodifurans as hole-transporting materials showed better performance than those using α-NPD, the current standard HTM. The hole drift mobility and the glass-transition temperatures of the tetraarylbenzodifurans were also found to be better than those of α-NPD.
Tsuji et al. (2007) studied this question.