Photo- and electro-luminescent properties of 2,7-disubstituted spiro[fluorene-9,9′-xanthene] derivatives containing imidazole-derived moieties

Two 2,7-disubstituted spiro[fluorene-9,9′-xanthene] derivatives, 2,7-bis(4-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl)spiro[fluorene-9,9′-xanthene] (SFX-2BI) and 2,7-bis(4-(1-(4-(tert-butyl)phenyl)-4,5-diphenyl-1H-imidazol-2-yl)phenyl)spiro[fluorene-9,9′-xanthene] (SFX-2IM), were synthesized by grafting the imidazole-derived moieties with different electron-withdrawing ability onto the 2- and 7-positions of spiro[fluorene-9,9′-xanthene] (SFX) core. Their photophysical and electrochemical properties, thermal stability and electroluminescent properties were investigated. The results showed that these compounds have excellent thermal stability and exhibit strong deep-blue emission in dichloromethane solution. In addition, the vacuum-processed doped and non-doped devices based on SFX-2BI and SFX-2IM were fabricated, in which the device prepared using SFX-2BI as the emitting material exhibited the best device performance with a turn-on voltage of 5.5 V, a maximum brightness of 3984 cd/m2, a maximum current efficiency of 3.65 cd/A and a maximum external quantum efficiency of 2.61%.