A diester of a fused ring compound of the formula (I): wherein: the fused rings are both aromatic; R1 and R4 to R6 substituents are H or ester moieties having C1 to C20 linear or branched alkyl chains; R2 and R3 are —C(O)OCxHy, wherein x is from 10 to 12 and y is from 21 to 25; two adjacent R1 to R4 substituents are —C(O)OCxHy, wherein x is from 10 to 12 and y is from 21 to 25; and when R3 and R4 are ester moieties, the alkyl chains of R4 are not C5 or C8; and polymer compositions containing the fused ring compound.