Optical films containing optical retardation-enhancing additive

An unstretched optical film comprising:

• (a) a cellulose ester polymer and
• (b) an additive having the structure below:
• wherein DISK represents a disk-like moiety having a fused ring structure, A is each independently —COO—, —OOC—, —CO—, —CONH—, —NHCO—, —O—, or —S—;
• Z is each independently an aryl, alkyl, ethoxylated alkyl, or ethoxylated aryl group, having 1 to 30 carbon atoms;
• Y is each independently a halogen or alkyl-, alkoxy-, or alkanoyl- group having 1 to 20 carbon atoms, m=0, 1, 2, 3, or 4;
• n is the number of the independent -A-Z substituents on the DISK, n=0, 1, 2, or 3,
• wherein the difference in the absolute value of the birefringence of the film with the additive and a similar film with triphenyl phosphate as the additive is greater than 0.0005.