TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: (V) are prepared by reacting 2,7-dibromo-9H-fluorene and dendritic carbazolyl alkyl bromide compounds of formula (VI), (VII) or (VIII) in mixed solvent of toluene and aqueous alkali at 50-90 degrees C under the action of catalyst for 4-24 hours, where the molar ratio of 2,7-dibromofluorene and (VI), (VII) or (VIII) is 1:1-6, the catalyst is tetrabutylammonium iodide, the molar ratio of the catalyst and 2,7-dibromo-9H-fluorene is 1-10:100, the aqueous alkali is aqueous sodium hydroxide or potassium hydroxide solution with the concentration of 10-70%. One of (VI) is 9-(12-bromododecyl)carbazole, prepared by reacting carbazole and 1,12-dibromododecane in 1:1 mixed solvent of toluene and aqueous alkali at 50-90 degrees C for 4-24 hours, where the molar ratio of carbazole and 1,12-dibromododecane is 1:1, the catalyst is tetrabutylammonium bromide and the molar ratio of the catalyst and carbazole is 1-10:100. One of (VII) is 3,6-di(carbazol-9-yl)-9-(12-bromododecyl)carbazole, prepared by (i) reacting 9H-carbazole with potassium iodide and potassium iodate in acetic acid solution at 50-150 degrees C for 0.5-4 hours to obtain 3,6-diiodocarbazole, where the molar ratio of carbazole, potassium iodide and potassium iodate is 1:0.9-2:3, (ii) reacting 3,6-diiodocarbazole and acetic anhydride in acetic anhydride at 50-150 degrees C under the action of catalyst for 0.1-4 hours to obtain 9-acetyl-3,6-diiodocarbazole, where the catalyst is boron trifluoride etherate, and the weight ratio of the catalyst and 3,6-diiodocarbazole is 1-15:100, (iii) performing Ullmann reaction of 9-acetyl-3,6-diiodocarbazole and carbazole in N,N-dimethylacetamide under the action of the promoter at 80-200 degrees C for 10-72 hours to obtain 9-acetyl-3,6-di(carbazol-9-yl)carbazole, where the molar ratio of 9-acetyl-3,6-diiodocarbazole and carbazole is 1:1.5-4, the promoter is cuprous oxide, and the molar ratio of the promoter and 9-acetyl-3,6-diiodocarbazole is 1-6:1, (iv) deacetylating 9-acetyl-3,6-di(carbazol-9-yl)carbazole in a mixed solvent of tetrahydrofuran, dimethyl sulfoxide and water according to the volume ratio of 1-50:1-20:1 in the presence of alkali at 40-100 degrees C for 0.5-6 hours to obtain 3,6-di(carbazol-9-yl)carbazole, where the alkali is sodium hydroxide or potassium hydroxide, and the weight ratio of the alkali and 9-acetyl-3,6-di(carbazol-9-yl)carbazole is 5-50:100, and (v) reacting 3,6-di(carbazol-9-yl)carbazole and 1,12-dibromododecane in a mixed solvent of toluene and aqueous alkali according to volume ratio of 1:1 at 50-90 degrees C under the action of catalyst for 4-24 hours to obtain 3,6-di(carbazol-9-yl)-9-(12-bromododecyl)carbazole, where the molar ratio of 3,6-di(carbazol-9-yl)carbazole and 1,12-dibromododecane is 1:1-5, the catalyst is tetrabutylammonium bromide and the molar ratio of the catalyst and 3,6-di(carbazol-9-yl)carbazole is 1-10:100.    TECHNOLOGY FOCUS - POLYMERS - Preparation (Claimed): The preparation of (I) comprises performing Stille coupling polymerization of side chain dendritic carbazolyl containing 2,7-dibromofluorene monomers of formula (V) and 4,7-di((2-(trimethylstannyl)thiophen-5-yl))-benzo(2,1,3)thiadiazole monomer in toluene solvent under the action of palladium catalyst at 8-150 degrees C for 4-48 hours, where the molar ratio of (V) and 4,7-di((2-(trimethylstannyl)thiophen-5-yl))-benzo(2,1,3)thiadiazole monomer is 1:1-1.02, the palladium catalyst is tetrakis(triphenylphosphine)palladium, and the molar ratio of the palladium catalyst and (V) is 10:100. Preferred Components: The number-average molecular weight of (I) is 3000-50000.