High Tg fluorene-based hole-transporting materials for organic light-emitting diodes

A new series of fluorene-based hole-tran sporting materials, 9,9-bis[4-(di-p-tolylamino)phenyl]-2,7-bis(diphenylamino)fluorene (1), 9,9-bis[4-(di-p-tolylamino)phenyl]-2,7-bis(di-p-tolylamino)fluorene (2), 9,9-bis[4-(di-p-tolylamino)phenyl]-2,7-bis(2-naphthylphenyl amino)fluorene (3), and 9,9-bis[4-(di-p-tolylamino)phenyl]-2,7-bis(9-carbazolyl)fluorene (4), was prepared and employed in the fabrication of organic light-emitting devices (OLEDs). These materials were designed to have bulky triarylamine moieties at the C-9 position, which provides them with excellent thermal stability and high glass-transition temperatures (T-g = 139-171 degrees C). 1 and 3 are comparable to 1,4-bis(1-naphthylphenylamino)biphenyl (NPB) in terms of device performance (maximum luminence and current efficiency) in a standard hole-transporting layer (HTL)/tris(8-hydroxyquinolino)aluminum (Alq(3)) double-layer device, but are superior to NPB in terms of higher glass-transition temperatures (T, = 139 and 145 degrees C, respectively), while 2 shows higher luminance and current efficiency as well as T-g (140 degrees C) than those of NPB (100 degrees C).