Electroluminescence of a bichromophoric molecule with a benzoxyazolylcoumarin and carbazole moiety

The electroluminescent properties of a bichromophoric molecule in which a benzoxyazolylcoumarin and carbazole moiety is combined with 1,2-ethylene linkage, i.e. 3-(2-benzoxyazolyl)-7-[2-(9-carbazolyl)ethoxy]-coumarin (CmCz), were investigated. CmCz exhibits fluorescence of different colors in a solid state and solution. Two types of device were made. One consisted of a vacuum vapor-deposited film of CmCz as an emission layer to utilize fluorescence in the solid state; the second consisted of a spin-cast film doped with CmCz as an emission material to utilize fluorescence in the solution. The device with a vapor-deposited CmCz film between electrodes shows a green emission with a luminance of less than 10^-2 cd/m². The multiple layer device in which the CmCz film was sandwiched between a hole transport layer and electron transport layer showed a green emission whose spectrum is identical to the photoluminescent spectrum in the vapor-deposited CmCz film. A maximum luminance of the multiple layer device is about 5000 cd/m². On the other hand, the devices consisting of a spin-cast film containing a hole transport material, an electron transport material and CmCz showed a blue emission whose spectra are identical to the photoluminescent spectrum of CmCz in chloroform. Luminance of these devices is over 100 cd/m².