NOVELTY - A fulvalene compound (I) is new.    USE - New fulvalene compound is used for fulvalene polymer for material used for forming light-emitting device, solar cell element and organic transistor element (all claimed). Can also be used for motor vehicles.    ADVANTAGE - The fulvalene compound is manufactured efficiently with high yield and reduced toxicity under mild conditions.    DETAILED DESCRIPTION - A fulvalene compound of formula (I) is new.    dotted circular arc=ring structure formed with portion of backbone moiety of 5-membered ring which forms fulvalene skeleton, preferably benzene ring, pyridine ring or thiophene ring;    X1-X4=H, monovalent substituent (a) chosen from bromo, methoxy, carboxy, -CO2CH3, -CH2OH, or substituent other than -CONHR, or monovalent substituent (b) other than monovalent substituent (a);    R=hydrocarbyl having phenyl;and    or two or more X1-X4=ring structure which forms dotted circular arc portion.    (i) When all of four ring structure of dotted circular arc are benzene rings, X1-X4 is not mutually bonded; (ii) All X1-X4 are does not have same structures; (iii) When X1-X4 is halo, At least 1 of X1-X4 is monovalent substituent other than halo; (iv) When X1 and X3 are same monovalent substituent (a), X2 and X4 are H or same monovalent substituent (b) different from X1 and X3; (v) When X1 and X4 are same monovalent substituent (a), X2 and X3 are H or same monovalent substituent (b) different from X1 and X4; (vi) When the ring structure bonded with X1 and X2 is naphthalene ring, the ring structure bonded with X3 and X4 is benzene ring, at least one of X3, X4 is monovalent substituents other than methoxy; (vii) When the ring structure bonded with X1 and X2 is pyridine ring, the ring structure bonded with X3 and X4 is benzene ring, or when all of X1-X4 are pyridine rings, at least 1 X1-X4 is monovalent substituent; and (viii) When all of four dotted circular arc ring structures are thiophene rings, X1-X4 are monovalent substituent other than H, bromo, 2-thiophene group, 5-bromo-2-thiophene group or alkyl, and sulfur atom of thiophene ring is bonded with X1-X4 respectively through two carbon atoms. INDEPENDENT CLAIMS are included for the following:    (1) manufacture of fulvalene compound;    (2) fulvalene polymer, which is obtained by polymerizing monomer component containing fulvalene compound (V); and    (3) solar cell material, which contains fulvalene polymer obtained by polymerizing monomer component containing compound having structure derived from fulvalene, or fulvalene compound.    X5-X8=X1, in which at least 1 of X5-X8 is substituent having reactive group.