A sensitizer in a dye-sensitized solar cell, including a compound of formula (I′) where: R1 and R2 are hydrogen, a halogen, an alkyl group, a cycloalkyl group, an aryl group, a hetaryl group, an alkoxy group, an aryloxy group, an arylthio group, a hetaryloxy group, a hetarylthio group, a diarylamino group, or a dialkylamino group; m, n are each independently an integer from 0-4; X is sulfur, oxygen, or NR3, where R3 is hydrogen, an alkyl group, a cycloalkyl group, an aryl group, or a hetaryl group; Y1 is oxygen or N—Z-A, where A is —COOM, —SO3M, or —PO3M, where M is hydrogen, an alkali metal cation, or [NR′]4+, where each R′ is independently hydrogen or an alkyl group, and where Z is C1-C6-alkylene or 1,4-phenylene, where the phenylene radical is optionally substituted by one or more alkyl, nitro, cyano, and halogen substituents.