Synthesis Of Meso-substituted Porphyrins And Their Electroluminescence Properties

It is vitally important to research the red emitting materials for developing full-color display of OLEDs. Porphyrins compounds are ideal red doping materials due to their unique luminescence properties, presently, the saturated red emission of red OLEDs doped by porphyrins is satisfactory for practical use, but there exist some problems, such as quantum efficiency and luminance of OLEDs are both low.In this paper, twenty novel meso-substituted porphyrins of four series were designed and synthesized by increasing the conjugation of porphyrins or introducing substituents (such as benzoazole, coumarin) with high fluorescence quantum yield into the meso-position of porphine, and then red OLEDs were fabricated by doping porphyrins into a suitable host using ten porphyrins compounds and their electrolumin -escence properties were tested. The main contents and results were generalized as follows:Three meso-tetrakis(triarylamine substituents)porphyrins 4a-c and three conjugations of porphine-triarylamine linked by styrene 10a-c were synthesized and characterized by 1H NMR, MS, UV-vis spectra and fluorescence emission spectra. The electronic interaction between the triarylamine units and porphines macrocycle in 4a-c and 10a-c were investigated by UV-vis absorption spectroscopy and fluorescence emission spectroscopy, and the results showed that there was a good energy transfer between triarylamine units and porphines. Thus, the absorbed energy by triarylamine units was reemitted by the porphyrins chromophore.Six porphyrins compounds 26a-f were obtained by introducing intensely fluorescence chromophore trans-stilbene, and characterized by 1H NMR, MS, UV-vis spectra and fluorescence emission spectra. Their UV-vis absorption spectra and fluorescence emission spectra were red shifted about 10 nm compared to tetraphenylporphyrin(TPP) as a consequence of expandedπ-conjugation.We firstly introduced benzoazole (including benzimidazole, benzoxazole and benzothiazole) into the meso-positions of porphines and obtained five new porphyrins 36a-e. Their structures were characterized by 1H NMR, MS, UV-vis spectra and fluorescence emission spectra. The molar extinction coefficient was lowered because of the presence of heteroatom (nitrogen, oxygen or sulphur) in above-mentioned molecules, so the UV-vis absorption was weakened, but the brightness of 36a-e fluorescence was increased.Due to their significant fluorescence chromophores, coumarins were introduced into the meso-positions of porphines and compounds 44, 45 and 46 were synthesized. Then their structures were characterized by 1H NMR, MS, UV-vis spectra and fluorescence emission spectra. The fluorescence spectra of 44, 45, 46 had a maximal peak at about 710 nm and a weak shoulder at about 650 nm because of steric hindrance and presence of C=O, and this was on the contrary of others porphyrins fluorescence spectra.To study the electroluminescence performance of 26f, the OLEDs devices were prepared with 26f as dopant and tris(8-hydroxyl quinoline)aluminum (Alq3) or N,N′-diphenyl-N,N′-di(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD) as host, and we studied the electroluminescence properties at different doping concentration. The luminance and efficiency of OLEDs were better than TPD when Alq3 was used as host, but the luminescence color was more pure when TPD was used as host. When the doping concentration of 26f in TPD was 1.5%, the luminescence color of OLED was red, and the maximal luminance and external quantum efficiency were 73 cd/m2 and 0.0365, respectively. The other nine OLEDs devices were fabricated with porphyrins as dopants and TPD as host, and we evaluated the electroluminescence performances of different series porphyrins at the same fabrication conditions of OLEDs. The best electroluminescence properties were obtained when 46 was used as dopant, and the maximal luminance and external quantum efficiency were 102 cd/m2 and 0.0408, respectively. The CIE coordinates were x=0.5703, y=0.3217.