Controllable photophysical properties and self-assembly of siloxane-poly(amidoamine) dendrimers

Poly(amidoamine) dendrimers are typical luminescent polymers containing unconventional chromophores. A series of novel siloxane-poly(amidoamine) (Si-PAMAM) dendrimers were synthesized and investigated in this study. Their structures and properties were determined by NMR, XPS, LC/MS, and fluorescence spectroscopy. The introduction of Si-O-Si units in Si-PAMAM changed the photophysical properties of the dendrimers. The luminescence of Si-PAMAM was associated with the aggregation of its carbonyl groups, which was caused by N -> Si coordination bonds. The strong blue luminescence of Si-PAMAM was also studied in detail, and it was found to be quite different from the ethanediamine-based poly(amidoamine). Results indicated that the luminescence of Si-PAMAM could be controlled by solvents, acids, metal ions, temperature, or degree of aggregation of the carbonyl groups. Moreover, micron-sized tubes composed of Si-PAMAM molecules were generated and found in water/methanol solution.