AMORPHOUS MOLECULAR MATERIALS - SYNTHESIS AND MORPHOLOGICAL-CHANGES OF A NOVEL ORGANIC PI-ELECTRON SYSTEM, 1,3,5-TRI(N-CARBAZOLYL)BENZENE

For the purpose of developing novel amorphous molecular materials and also gaining information on the relationship between molecular structu re and glass-forming properties, a novel organic pi-electron system, 1 ,3,5-tri-(N-carbazolyl)benzene (TCB), was synthesized and its glass-fo rming properties investigated. Whereas 1,3,5-triphenylbenzene and 1,3, 5-tris(diphenylamino)benzene instantly crystallized even when their me lt samples were rapidly cooled with liquid nitrogen, TCB was found to readily form an amorphous glass via a supercooled liquid when the melt sample was cooled even at a cooling rate of 5 degrees C min(-1) as we ll as with liquid nitrogen, as characterized by DSC, XRD, and polarizi ng microscopy. It is suggested from the CPK model that a nonplanar mol ecular structure of TCB with a bulky, planar carbazole ring significan tly twisted from the plane of the central benzene ring is responsible for the formation of the glass. The TCB glass was found to exhibit a m uch higher glass-transition temperature (T-g) of 122 degrees C than th e glass of a related compound, 1,3,5-tris(4-methylphenylphenylamino)be n (T-g: 58 degrees C). This result indicates that the incorporation of a rigid moiety such as carbazole serves as a guiding principle for in creasing T-g. TCB was found to exhibit polymorphism, taking two differ ent crystal forms. That is, the crystal obtained by sublimation in vac uo differs from the crystal formed when the amorphous glass is heated above the T-g.