Exciplex elimination in an organic light-emitting diode based on a fluorene derivative by inserting 4,4'-N,N'-dicarbazole-biphenyl into donor/acceptor interface

Organic light-emitting diodes （OLEDs） composed of a novel fluorene derivative of 2,3-bis（9,9-dihexyl-9H-fluoren- 2-yl）-6,7-difluoroquinoxaline （F2Py） were fabricated, and exciplex emission was observed in the device. To depress the exciplex in an OLED for pure colour light emission, 4, 4＇-N,N＇-dicarbazole-biphenyl （CBP） was inserted as a separator at the donor/acceptor interface. It was found that the device without the CBP layer emitted a green light peaking at 542 nm from the exciplex and a shoulder peak about 430 nm from F2Py. In contrast, the OLED with CBP layer emitted only a blue light peak at about 432 nm from F2Py. Device efficiencies were calculated by a simulative mode in an injection controlled type mechanism, and the results showed that exciplexes yield much lower quantum efficiency than excitons. The device with CBP has a higher power efficiency as no exciplex was present.

Structural and Magnetic Characterization of Two New Coordination Compounds Based on a Fluorene Derivative Ligand

Two new coordination compounds[Co(FDC)_(2)(H_(2)O)_(2)]_(n)(1)and[Cu(FDC)_(2)(2,2?-bpy)]·DMF·H_(2)O(2)(HFDC=9-fluorenone-4-carboxylic acid,bpy=2,2?-bipyridine,DMF=N,N-dimethylformamide)were prepared by the reactions of corresponding metal salts with a fluorene derivative ligand of HFDC.Both compounds were thoroughly analyzed by X-ray single-crystal diffraction,elemental analysis,IR spectra,PXRDand thermal analysis.Compound 1 features a 1D structure.Via two kinds of O?H···O hydrogen bonds,such 1Dchains self-assemble into a 3D supramolecular structure stabilized by the offset face-to-faceπ···πinteractions.Compound 2 features a dinuclear structure which,via O?H···O and C?H···O hydrogen bonds,self-assembles into a 2D supramolecular layer strengthened by strong face-to-faceπ···πinteractions.And variable-temperature magnetic susceptibilities of 1 and 2 indicate weak antiferromagnetic interactions between the Co(II)and Cu(II)metal ions.

Theoretical Investigation on the Electron and Energy Transfer between Peripheral Carrier Transport Groups and Central Chromophores in Electroluminescent Materials

The molecular materials with structures of luminescent core and peripheral carrier groups （e.g. carbazoles）, have exhibited high-performance in organic light-emitting diodes （OLEDs）. Present work is to understand the basic process of electronic and energy exchange between the peripheral functional groups and the central core through quantum chemical analysis. As an example, 4,7-bis（9,9-bis（6-（9H-carbazol-9-yl）hexyl）-9H-fluoren-2-yl）benzo[c]- [1,2,5]thiadiazole （TCBzC） is investigated in regards to optoelectronic properties using density functional theory （DFT）. The results suggest that the forbidden transition from peripheral carbazole to the central chromophore core makes for separated electrical and optical properties, and high performance electroluminescence （EL） is mainly at- tributed to the energy-transfer from carbazoles to the fluorene derivative core.