The syntheses of a series of oligo (phenylene vinylenes) (OPVs) were described. The extended π-chains were built up by sequences of Wittig reactions. Their electronic structures were systematically studied with absorption spectra, photo-luminescent spectra. The influences of the effective conjugation length on the performance of the light emitting devices were investigated.
A stable red organic light-emitting device has been realized by doping a red dye tetra-methyljuloidine (DCJT)in electron transporting layer(ETL). The structure of the device was ITO/ CuPc/ NPB/ Alq: DCJT/ MgAg, where copper phthalocyanine(CuPc) was used as a buffer layer, N, N ’-his-(1-napthyl)-N, N’- diphenyl-1, 1’ -biphenyl-4, 4’ -diamine(NPB) as the hole transporting layer, tris(8-quinolinolato) aluminum complex(Alq) as ETL, in which DCJT was doped, indium tin oxide(ITO) and MgAg were as the anode and cathode, respectively. The red emission with peak at 620nm and CIE coordinates x = 0. 63, y = 0. 37, maximum luminance 4 687cd/m2, maximum luminous efficency 0. 83lm/W were obtained. The device showed a high stability under 12mA/cm2 current density continuous operation, the half decay time reached 2 500 hours at the initial luminance 150cd/m2 and the change of driving voltage was 0. 6mV/hour in the degradation process. If 50cd/m2 is taken as the initial luminance of red device, the half decay time is considered to be 7 500 hours. (According to European Broadcasting Union(EBU) standard, for color display the ratios for red, green, blue luminance should be 30 %, 59 % and 11 %, respectively, since 100cd/m2 is often used as initial luminance of green emission in degradation test, 50cd/m2 should be adapted as the initial luminance for red emission. )
A series of squarylium cyanine dyes (Sqs) were synthesised to explore their applications in functional devices. Preliminary investigation on the mechanism involved in these devices was carried out. Spectroscopic behavior of Sqs with porphyrin (P), 8-hydroxyquinolium aluminum (Alq) and ruthenium bipyridyl complex (Ru(bipy)) in solution, in film and on nanocrystalline TiO2 was investigated, respectively. A mechanism including photoinduced energy transfer and charge transfer processes was suggested in the corresponding practical devices. By means of doping, a red organic electroluminescent device (ELD) using Sq-doped Alq as the emission layer (EML) has been developed, and the total light to electricity efficiency of nanocrystalline TiO2 electrode based on using Sq-doped Ru(bipy) M photosensitizer has been improved greatly in the whole visible region, particularly in the red area above 600 nm.
