NOVELTY - Benzoindole-based compounds (I) are new.    USE - (I) are useful in a dye, which is useful in a dye-sensitized solar cell (claimed).    ADVANTAGE - (I) can be easily introduced by a desired substituent and easily prepared with high purity. (I) are prepared at low cost, has high molar absorption coefficient and high photoelectron conversion efficiency. The dye is prepared at a low cost, than the conventional ruthenium dye, and has excellent photoelectric conversion efficiency.    DETAILED DESCRIPTION - Benzoindole-based compounds of formula (I) are new.    A, B1 = H or -D-E, where both A and B1 are not H;    D = 6-20C aryl, 2-20C heteroaryl, 4-20C carbocyclic and/or 4-20C heterocyclic (all optionally substituted);    E = acidic functional (preferably carboxyl, phosphorous acid, sulfonic acid, phosphinic acid, OH, oxycarboxylic acid, acid amide, boric acid and/or squaric acid);    R = 1-20C alkyl group, 6-20C aryl, 2-20C heteroaryl, 4-20C carbocyclic and/or 4-20C heterocyclic (all optionally substituted) (preferably fluorene);    R0 = 1-20C alkyl, halo, CN, 1-20C alkoxy, 1-20C alkylamino, OH, 6-20C aryl, 1-20C alkylthio, amino, 6-20C aryloxy, 2-20C heteroaryl, 4-20C heterocyclic, 2-20C alkenyl and/or 2-20C alkynyl; and    s = 0-5.    INDEPENDENT CLAIMS are included for:    (1) a dye, for a dye-sensitized solar cell, comprising (I); and    (2) a dye-sensitized solar cell comprising a first electrode (11) and a second electrode (21) disposed to face each other, and a porous film (13) disposed between the first electrode and the second electrode in which a dye (15) is adsorbed to produce a voltage potential between the first electrode and the second electrode from absorption of light, where the dye comprises (I).    DESCRIPTION OF DRAWING(S) - The diagram shows a cross-sectional view illustrating the dye-sensitized solar cell.    First substrate (10)    First electrode (11)    Porous film (13)    Dye (15)    Second substrate (20)    Second electrode (21)    Electrolyte. (30)