Reflection grating photorefractivity of molecular glasses of novel star-shaped molecules end-caped with carbazole moiety, alpha,alpha',alpha ''-tris-(4-(carbazoryl)-n-hexyloxyphenyl)-1,3,5-triisopropylbenzene (Tris) and alpha,alpha,alpha',alpha'-tetrakis-(3,5-dimethyl-4-(6-carbazoryl-n-hexyl oxy)phenyl)-p-xylene (Tetrakis) is presented. Large asymmetric two-beam coupling (asymmetric energy transfer) was achieved in reflection grating geometry. Highest net gain coefficient of 33 cm(-1) With optical gain of 53 cm(-1) and absorption coefficient of 19.7 cm(-1) was obtained for Tetrakis composite at applied electric field of 57.7 V/mu m. Effective large trap density is associated with high photorefractive optical gain. (c) 2005 Elsevier B.V. All rights reserved.