Mixed films of nonamphiphilic N,N’-bis(2,5-di-tert-butylphenyl)-3,4,9,10-perylenedicarboximide (DBPI) and stearic acid (SA) have been studied at the air-water interface and as Langmuir-Blodgett (LB) films deposited on glass substrates. Our studies reveal that DBPI forms excellent LB mono- and multilayers mixed with SA that are highly fluorescent. Spectroscopic studies indicate the formation of organized aggregates in the LB films that is evident from the broadening of the absorption spectral profile and the appearance of a broad band excimer-like emission that originates from a loosely bound dimer of DBPI. While freshly prepared LB films exhibit the excimer-like broad band maximum at 602 nm, aging of the films results in a shift of the excimer-like band maximum from 620 nm for a three week old film to 636 nm for a film that is twelve weeks old. The observed spectroscopic changes are attributed to the changes in the packing configuration of the DBPI moieties in the LB films with time.