Pyrenoimidazole-based Material:Synthesis And Characteristic Study

Organic light-emitting devices(OLEDs)received more and more attention due to their applications in full-color display and solid-state lighting.Both pyrene and1,3-imidazole are important materials in OLED field.Pyrene,a polycyclic aromatic hydrocarbon,which is plane,symmetric and easy to modify.1,3-imidazole is a stably five-numbered-ring,which amphoteric characteristics has two different kinds of sp2 hybrid nitrogen atoms.The unique structure brings affermative effect on energy level structure and charge transport ability.Characteristics are always decided by molecular structures,the category,size and number of the substituents,which bring conjugation effect,steric hindrance effect,electron inductive effect,have a great influence on the photoelectronic properties including the excited state properties.Base on this concern,a new type molecular which called pyrenoimidazole,was created using pyrene and imidazole as the key units.We try to investigate the relationship between molecular structures and properties by introducing anthracene unit.As following works:1.PyI-C2-An and PyI-N1-An are obtained by introducing anthracene in C2 and N1 position of 1,3-imidazole.Both of them are chemically stable and thermostable to prepare for light-emitting diodes.PyI-C2-An has single peak value in the emission spectrum in solution state and has an obvious solvation effect.While,PyI-N1-An shows bifluorescence phenomenon at the same time.In other words,they have different excited state.When in film state,the bifluorescence of PyI-N1-An disappears and the two compounds show single peak value in the emission spectrum.Two doped devices are obtained by using PyI-C2-An and PyI-N1-An as emitting material.The turn-on voltages are 3.0 V and 6.9 V respectively,the external quantum efficiency are 3.19% and 2.17% separately and the luminance efficiency are 2.97%and 2.40% respectively.2.DPyI-C2-An and DPyI-N1-An are obtained based on PyI-C2-An and PyI-N1-An by introducing another pyrenoimidazole group.Both DPyI-C2-An and DPyI-N1-An have much better chemical and thermodynamic stability due to their rigid structures.Compared with PyI-N1-An,the bifluorescence of DPyI-N1-An is invisible neither in solutions nor in films.Moreover,the large conjugation extent alsobrings red-shift to a certain extent.Nondoped and doped devices are obtained by using DPyI-C2-An and DPyI-N1-An as emitters.All of them have low turn-on voltage,and the nondoped devices show higher luminance efficiency and external quantum efficiency.Moreover,DPyI-N1-An behaves better OLED properties due to is large dihedral angle between molecular units.