Entrapment and Rigidification of Adenine by a Photo-Cross-Linked Thymine Network Leads to Fluorescent Polymer Nanoparticles

Photo-cross-linking of nucleobase-containing polymer micelles was observed to result in fluorescent polymer nanoparticles. By varying the micelle assembly conditions, it was possible to probe the origins of this behavior. A number of factors were investigated, including the effect of omitting one of the nucleobases, blocking hydrogen-bonding interactions, detaching the nucleobase from the polymer backbone, and changing the degree of core cross-linking. Spectroscopic investigations were also carried out to further characterize the fluorescent nanoparticles. These data revealed that no new small molecule fluorophores were created during cross-linking and that a dense, hydrogen-bonded network of photodimerized thymine with entrapped adenine was required for fluorescence to arise. We conclude that rigidification and immobilization of adenine in this way leads to the enhancement of an already extant fluorescence pathway and suggests that synergistic covalent and supramolecular entrapment of profluorophores may provide a general strategy for the production of novel fluorescent polymer nanoparticles.