The present invention relates to cyanated naphthalenebenzimidazole compounds of the formula (I) and mixtures thereof, in which R1, R2, R3, R4, R5, R6, R7, R8, R9 and R10 are each independently hydrogen, cyano or aryl which is unsubstituted or has one or more identical or different substituents RAr, where RAr is as defined in the claims and in the description, with the proviso that the compounds of the formula I comprise at least one cyano group. The invention further relates to color converters comprising at least one polymer as a matrix material and at least one cyanated naphthalenebenzimidazole compound or mixtures thereof as a fluorescent dye, to the use of the color converters and to lighting devices comprising at least one LED and at least one color converter.