A series of three pentacene derivatives featuring substituted aryl groups at the 6,13-position, namely, 6,13-diphenylpentacene, 6,13-bis(2,6-dimethylphenyl)pentacene, and 6,13-bis(4-tert-butylphenyl)pentacene, have been synthesized and characterized. The optical properties of each compound have been determined in solution and in the solid state. Films containing the pentacene derivatives dispersed in tris(quinolin-8-olato)aluminum(111) (Alq(3)) emit in the red with small contribution from the Alq3 host, signaling efficient energy transfer from host to guest molecules. The absolute photoluminescence quantum yield (phi(PL)) of composite films is similar to30-32% at optimum dopant concentration. Organic light-emitting diodes based on these composite films as the active emitting layers have been fabricated and characterized. External electroluminescence quantum efficiencies near the theoretical limit have been achieved.