NOVELTY - A methine group pigment (1) is new.    USE - For sensitizing oxide semiconductor microparticles in optoelectric transducers used for solar cells (both claimed).    ADVANTAGE - The new methine group pigment provides optoelectric transducers which improve the photoelectric conversion efficiency and stability of solar cells.    DETAILED DESCRIPTION - A methine group pigment of formula (1), is new.    n=0-7;    R1,Z=optionally substituted aromatic residue or aliphatic hydrocarbon residue, or acyl;    X=optionally substituted 2-4C hydrocarbon residue, or coupling group which forms heterocyclic ring with nitrogen bonded with benzene ring (a);    Y'=H, optionally substituted aromatic residue or aliphatic hydrocarbon residue, carboxyl, phosphoric acid group, sulfonic acid group, cyano, amide, or alkoxy carbonyl;and    A1-A3=H, optionally substituted aromatic residue or aliphatic hydrocarbon residue, hydroxyl, phosphoric acid group, cyano, halogen, carboxyl, carbon amide, alkoxy carbonyl, aryl carbonyl, or acyl.    When n is except 0, A1, A2 and/or A3 form a ring which may have a substituent, and further a ring with benzene ring (a). Benzene ring (a) may have substituent other than X, chosen from nitrogen, halogen, amide, hydroxyl, cyano, nitro, alkoxyl, optionally substituted aromatic residue or aliphatic hydrocarbon residue, optionally substituted amino, and acyl. The substituents may form a ring which bond with A1-A3 and may have substituent.    INDEPENDENT CLAIMS are included for:    (1) optoelectric transducer using oxide semiconductor microparticles sensitized with the methine group pigment;    (2) solar cell including the optoelectric transducer; and    (3) aldehyde compound of formula (1a).    n=0-2;    Xa=-CH2CH2- or -(CH2)3-;    R1=fluorene-2-yl group which may have 6-18C alkyl or 9,9-dimethyl substitution; and    A2,A3=H.    When n is 2, first A2 and last A3 bond together to make a coupling group which consists of sulfur atom. When forming a thiophene ring, remaining A2 and A3 are H. The benzene ring does not have any substituent other than Xa and nitrogen atom.