Dynamic fluorescence probing of the local environments within amphiphilic starlike macromolecules

Steady-state and time-resolved fluorescence spectroscopies were used to investigate the local environments of coumarin 102 (C102) probe molecules when encapsulated within an amphiphilic starlike macromolecule (ASM). ASMs are promising surfactant-type nanoscale transporters of hydrophobic drug molecules. They consist of a hydrophobic core, in which small, hydrophobic molecules such as C102 can be encapsulated, and a hydrophilic shell that makes the whole assembly water-soluble. Steady-state fluorescence spectroscopy revealed that C102 molecules sense a very polar environment when encapsulated in ASMs. Both time-correlated single-photon counting and fluorescence upconversion techniques indicated that the solvent reorganization and diffusive reorientation of the C102 solvatochromic fluorescent probe are significantly slowed compared to the rates in aqueous solutions. These results provide insight into the dynamics of drugs encapsulated within ASMs.