Synthesis Of Tetraarylsilane & Studies On Their Organic Electroluminescent Properties

Tetrahedral dendrimers,as one class of 3-dimentional dendritic organic compounds have attracted much attention in the field of chemistry and material science.Such materials are found less prone to self-aggregation in the solid state due to their stereo hindered structures,so they have been developed and investigated as light-emitting materials.To date,most tetrahedral light-emitting organic compounds were prepared from a tetraphenylmethane core,however,only a few tetraarylsilane cores applied were reported in literature.A series of tetraarylsilane(TS1-TS9) were synthesized and characterized by ¹HNMR,¹³CNMR and MS.Their thermal stability was measured by TGA and DSC, which showed very high decomposition temperature(440-560℃) of them. Compounds TS1-TS4 were fabricated into organic light-emitting devices to investigate their electroluminescence properties with device configuration of ITO/NPB(40 nm)/TS1-TS4(26 nm)/TPBI(33 nm)/LiF(1.2 nm)/ Al(200 nm),in which compounds TS1,TS2,TS3 and TS4 were used as emitting layer,respectively. Blue emission was achieved by all the devices based on TS1,TS2,TS3 and TS4 with peaks at 438,445,435and 428nm,respectively.Moreover,the luminance efficiency of TS1,TS2,TS3 and TS4 at 100mA/cm² was measured as 0.57,0.31,0.11 and 0.73 cd/A,respectively.TS1 based device showed the lowest turn-on voltage of 5.5V, with a highest brightness of 907cd/m² at 12.5 V.Phenomenon of Aggregation-induced emission(AIE) was first observed in silole derivatives which were found to be faintly emissive in ethanol or chloroform solution, but their aggregates and solid films were strongly luminescent.Here we synthesized a series of tetraarylsilane derivatives TS5-TS9 and found that TS5,TS6,TS7 showed good AIE property.The photoluminescence(PL) spectra and UV-visible absorption spectra were measured to characterize the AIE feature in tetrahydrofuran(THF) and in THF-water mixture,respectively.Furthermore,by observing and comparing their transmission electron microscopy(TEM) images,we found that the relative emission intensity of nanoparticle is size-dependent.The smaller the nanoparticle size,the higher quantum yields it presents.Some of styrylbenzene derivatives that have been reported are AIE-active,such as (1-cyano-trans-1,2-bis(4-methylbiphenyl)ethylene(CN-MBE).Here we reported the methyl substituted styrylbenzene derivatives(MBE1-MBE4) which also showed the AIE phenomena.The quantum yields greatly increased when certain amount of poor solvent like water was added into the solution of MBE1-MBE4.Experimental data also showed decreasing the solutions' temperature enhanced the emission,which indicate that these AIE phenomena were probably caused by the restricted intramolecular rotation.