Transient absorption studies have been carried out on structurally similar 4-aminophthalimide derivatives, wherein the amino nitrogen forms part of a cyclic system of different ring sizes, with a view to rationalizing the dependence of fluorescence quantum yield of the systems on the polarity and hydrogen bond donating ability of the media. The results suggest that an enhanced internal conversion process is responsible for the reduction of fluorescence efficiency of the aminophthalimides in highly polar and protic media. (c) 2007 Elsevier B.V. All rights reserved.