Polymer−Dye Complexes: A Facile Method for High Doping Level and Aggregation Control of Dye Molecules

We show that strong noncovalent interactions between a host polymer and guest dye molecules drastically suppress the dye aggregation tendency, thereby allowing high doping levels, which in turn opens possibilities for enhanced performance. We use a common azo-dye (Disperse Red 1) and three polymer matrixes: polystyrene (PS), poly(4-vinylphenol) (PVPh), and poly(styrenesulfonic acid) (PSSA). The polymer−dye systems are studied in thin films by ultraviolet−visible and infrared spectroscopy and by optical second-harmonic generation. The lack of interaction in PS-matrix limits the maximum obtainable dye loading without aggregation below 20 wt %. Due to the polar nature of PVPh matrix, ca. 40 wt % dye loading can be achieved without aggregation, whereas in PSSA an ionic complex is formed, allowing ca. 60 wt % loading. In the latter case a dye molecule is attached to approximately each polymer unit, which has typically required covalent bonding of dye molecules to the polymer. This motivates further studies of noncovalently interacting guest−host systems as a general route for functional optical materials.