Energy transfer in supramolecular assemblies of oligo(p-phenylene vinylene)s terminated poly(propylene imine) dendrimers

Poly(propylene imine) dendrimers have been functionalized with pi-conjugated oligo(p-phenylene vinylene)s (OPV's) through an amide linkage and are fully characterized. In solution the dendrimers behave as globular entities without specific interactions between the OPV units. The OPV dendrimers have an amphiphilic nature and self-assemble at the air-water interface forming stable monolayers in which the dendritic surfactants presumably adopt a cylindrical shape; all the OPV's are aligned perpendicular to the water surface, and the dendritic poly(propylene imine) cores face the aqueous phase. Optical spectra taken from Langmuir-Blodgett films show a small blue shift indicative of interactions between the OPV units. Spin-coated homogeneous thin films could be obtained from solutions containing dendrimers loaded with dyes. The optical properties of these films are similar to the Langmuir-Blodgett films which points to the same type of organization of the OPV's. The OPV dendrimers are effective extractants of anionic dye molecules from water to organic solvents. Ratios between dye and dendrimer can be easily tuned by varying the concentration of dye in the water layer. The host-guest assemblies show not complete energy transfer from the OPV units to the encapsulated dye molecules in solution. The energy transfer is very efficient in spin-coated films of dendrimer/dye assemblies and the emission wavelength can be adjusted by using a variety of dye molecules. The dendrimer/dye systems mix very well with poly(p-phenylene vinylene)s (PPV's) forming good quality thin films in contrast to films obtained from dye/PPV without dendrimer. The OPV units in the dendrimer act as a compatibilizer in these systems and energy transfer is observed from the organic PPV polymer to the dye. It gives the possibility of tuning the emission wavelength of the PPV thin films by using the appropriate encapsulated dye.