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

Abstract

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.

Advances in Light‐Emitting Dendrimers

“…The photophysical properties and self‐assembly of siloxane–PAMAM dendrimers 175 ‐PG1 and 176 ‐PG2 were also studied. The outcomes confirmed that the fluorescence of Si–PAMAM could be changed by solvents, acids, metal ions, temperature, and aggregation degree of carbonyl groups ( Figure ) …”

“…This is because acetone changed the aggregation of the carbonyl groups and physically influenced the configuration of Si–PAMAM. In water, Si–PAMAM aggregated because of its solubility, and the aggregation enhanced emission phenomenon was observed, which demonstrated that the fluorescence intensity was increased with the addition of volume fraction of water …”

“…Fluorescence spectra of 176‐ PG2/methanol (concentration of 176‐ PG2 was 4 mg mL −1 ) at 363 nm. Reproduced with permission . Copyright 2015, The Owner Societies.…”

Nonconventional Luminescence Enhanced by Silicone‐Induced Aggregation

“…[6,19] Some reports attributed the emission to aggregation of carbonyl groups. [20] In the case of hyperbranchedp olyether epoxy,t he aggregation of the highly dense epoxy groups were responsible for fluorescencee mission. [12] However,t hesem echanismsw ere too specific to summarize the fluorescence emission for all of the nonconventional luminogens.…”

“…Previous reportsh ave shown that the structural features of fluorescent polymers, dendrimers or supramolecular assemblies can easily make the nonconventional chromophores aggregated to form extended conjugation because of chain entanglement, dendritic effect, and intermolecularf orces. [11,20] Compared to these polymers, the presents iloxane derivatives are small and simple. In other words, the molecules should be theoretically monodispersed in dilute solutions, andt he conjugation should not be bulky enough to emits trong fluorescence.H owever, simple siloxane derivatives, including BSCN, BSMA and Si-PAMAM( Figure S5,S upporting Information), can emit bright blue fluorescence in dilute solutions.…”