Synthesis And Characterization Of Near-Infrared Organic Electroluminescent Materials

The near-infrared(NIR) organic light-emitting diodes(OLEDs) is presently an interesting subject. Donor-acceptor-donor(D-A-D) chromophores have served as an important class of NIR materials for NIR OLED applications. A series of donor-acceptor-donor type of near-infrared(NIR) fluorescent compounds are synthesized by Suzuki cross-coupling reaction based on the electron acceptors of benzothiadiazole and its selenium analogues and the electron donors of carbazole,phenothiazine and triphenylamine. All the intermediates and target comcounds are characterized by 1H-/13C-NMR, IR and elemental analysis. Their thermal property is characterized by thermogravimetric analysis(TG) and differential scanning calorimetry(DSC). All the target compounds show an excellent thermal stability, which is indicated by the onset temperatures(Td) above 350 oC. The absorption and fluorescent properties of for all the target compounds are also studied by UV-vis and FL. The absorption maxima ranges from 505 nm to 575 nm and the fluorescence maxima from 668 nm to 756 nm. Their band gaps are located between 2.09 e V and 1.80 e V. High thermal stability and glass transition temperatures allow these chromophores to be used as emitters, which can be spin-coated for the OLED fabrication. The electroluminescent spectra of the devices with these new chromophores as active layers cover a range from 675 nm to 802 nm. The introduction of thiophene groups or the replacement of sulfur with selenium can lead to the red shift of emission maxima and the reduction of band gaps.A novel hyperbranched conjugated polymer(HPTPA-BTz) and its model compound(TPA-BTz) with triphenylamine(TPA) and benzotriazole moieties are synthesized by Suzuki cross-coupling reaction. The chemical structures of HPTPA-BTz and TPA-BTz are characterized by 1H-NMR, FT-IR and GPC. The photophysical properties are investigated by UV-vis, steady and transient fluorescent spectra. Although the same emission maxima(524nm) are obtained from their tetrahydrofuran dilute solutions, the fluorescent lifetime is decreased from 4.70 ns of TPA-BTz to 3.08 ns of HPTPA-BTz. The electroluminescent spectra of HPTPA-BTz exhibit the EL emission maximum of 523 nm.