Dye−Polyelectrolyte Layer-by-Layer Self-Assembled Materials: Molecular Aggregation, Structural Stability, and Singlet Oxygen Photogeneration

The interaction of rose Bengal (RB) and fluorescein (FL) with poly[diallyldimethylammonium] chloride (PDDA) was studied in layer-by-layer self-assembled thin films and in solution. The spectroscopic behavior is explained in terms of dye-dye, dye-polyelectrolyte, and in solution, dye-solvent interactions. A correlation among dye hydrophobicity, aggregation tendency, polymer folding in solution, and the stability of self-assembled films is obtained. In spite of the very high dye concentration (approximately 1 M), RB-PDDA multilayer thin films are able to photogenerate singlet molecular oxygen, as demonstrated by chemical monitoring and IR phosphorescence detection.