NOVELTY - A symmetrical benzimidazole-ruthenium complex comprises pyrenyl in which symmetrical pyrenyl of ruthenium complex both ends are fixed ligand and auxiliary ligand, and complex is formed by coordinating 3 nitrogen (N) atoms of imidazole ring in benzimidazole derivative and ruthenium metal ion.    USE - A symmetrical benzimidazole-ruthenium complex for solar cell.    ADVANTAGE - Process is simple and low cost, product has excellent photosensitive dye, good stability and electrochemical property, and high purity, and raw material is easy to get and purify.    DETAILED DESCRIPTION - A symmetrical benzimidazole-ruthenium complex of formula (I) comprises pyrenyl in which symmetrical pyrenyl of ruthenium complex both ends are fixed ligand and auxiliary ligand, and complex is formed by coordinating 3 nitrogen (N) atoms of imidazole ring in benzimidazole derivative and ruthenium metal ion. An INDEPENDENT CLAIM is included for preparation of symmetrical benzimidazole-ruthenium complex which involves dissolving 1-bromo-3,5-dimethoxybenzene into anhydrous N,N-dimethylformamide (DMF) under nitrogen atmosphere, continuously adding pinacol diborane, potassium acetate (KOAc), and 1,1'-bis(diphenylphosphino)ferrocene-palladium(II)dichloride dichloromethane complex (PdCl2(dppf).CH2Cl2), stirring at 90 degrees C, steaming, extracting, dehydrating, purifying into column chromatography to obtain 3,5-dimethoxybenzene boronic acid pinacol ester, dissolving obtained 3,5-dimethoxybenzene boronic acid pinacol ester and 4-bromo-2,6-bis(2-(1-methyl)benzimidazolyl)pyridine into anhydrous DMF under nitrogen atmosphere, continuously adding KOAc and PdCl2(dppf).CH2Cl2, stirring at 90 degrees C, distilling, extracting, dehydrating, purifying into column chromatography, recrystallizing to obtain 4-(3,5-dimethoxybenzene)-2,6-bis(2-(1-methyl)benzimidazolyl)pyridine, dissolving obtained 4-(3,5-dimethoxybenzene)-2,6-bis(2-(1-methyl)benzimidazolyl)pyridine into anhydrous dichloromethane (CH2Cl2) under nitrogen atmosphere, dropping tribromoborane (BBr3), stirring, quenching, extracting, washing, recrystallizing to obtain 4-(3,5-dihydroxyphenyl)-2,6-bis(2-(1-methyl)benzimidazolyl)pyridine, dissolving obtained 4-(3,5-dihydroxyphenyl)-2,6-bis(2-(1-methyl)benzimidazolyl)pyridine and 1-(4-bromobutyl)-pyrene into DMF solution, adding potassium carbonate (K2CO3), stirring at 80 degrees C, distilling, extracting, dehydrating, distilling, purifying into column chromatography to obtain 4-(3,5-bis(oxy-1,4-butylene-pyrenyl))-2,6-bis(2-(1-methyl)benzimidazolyl)pyridine, dissolving ruthenium(III) chloride trihydrate (RuCl3.3H2O) into glycerol solution under nitrogen atmosphere, dissolving obtained 4-(3,5-bis(oxy-1,4-butylene-pyrenyl))-2,6-bis(2-(1-methyl)benzimidazolyl)pyridine into anhydrous DMF, dropping RuCl3.3H2O organic solution into reactor, reacting at 150 degrees C under stirring condition, cooling, adding potassium hexaflorophosphate (KPF6) solution, pouring into water, filtering, washing, drying, and purifying into polyacrylamide gel chromatography in which molar ratio 1-bromo-3,5-dimethoxybenzene:pinacol diborane is 1:1-2, molar ratio 4-bromo-2,6-bis(2-(1-methyl)benzimidazolyl)pyridine:3,5-dimethoxybenzene boronic acid pinacol ester is 1:1-2, molar ratio 4-(3,5-dimethoxybenzene)-2,6-bis(2-(1-methyl)benzimidazolyl)pyridine:BBr3 is 1:2.5-5, molar ratio 4-(3,5-dihydroxyphenyl)-2,6-bis(2-(1-methyl)benzimidazolyl)pyridine:1-(4-bromobutyl)-pyrene is 1: 2-2.5, and molar ratio RuCl3.3H2O:4-(3,5-bis(oxy-1,4-butylene-pyrenyl))-2,6-bis(2-(1-methyl)benzimidazolyl)pyridine is 1:2-2.5.