Self assembly of block copolymers has gained considerable attention because of its potential use in various areas such as medical and biomedical applications, nanotechnology, and electronics. Herein, we present the synthesis and characterization of amphiphilic block-random copolymers with a covalently incorporated pH-sensitive dye, namely eosin. Ring opening metathesis polymerization was chosen for the preparation of well defined block copolymers and block-random copolymers using a modified "2nd Generation Grubbs" initiator. The self assembly behavior of the block-random copolymers in solution was studied by dynamic light scattering and small angle X-ray scattering (SAXS). The influence of dye incorporation on the result of the self assembly process in methanol and ethanol was investigated and a subtle interplay of the nature of the selective solvent, the chain-length of the block copolymer and the position of the dye within the polymer chain was established. Structural investigations using SAXS revealed a spherical shape and a core-shell structure of exemplary block and block-random copolymer micelles. UV-vis absorption and photoluminescence measurements revealed similar optical properties for polymer micelles in methanol compared to polymer solutions in THF. The pH-sensitive behavior of the eosin dye was preserved within the micelles. (C) 2007 Wiley Periodicals, Inc.