Unexpected Strong Blue Photoluminescence Produced from the Aggregation of Unconventional Chromophores in Novel Siloxane–Poly(amidoamine) Dendrimers

Abstract

Poly­(amidoamine) (PAMAM) dendrimers and hyperbranched poly­(amidoamine)­s are the first reported and most investigated luminescent polymers containing unconventional chromophores. The luminescence of these compounds is associated with the N-branched tertiary amine moiety, and the oxidation of the tertiary amine is assigned to the emitting source. However, in this paper, a series of novel siloxane–poly­(amidoamine) (Si-PAMAM) dendrimers were synthesized by aza-Micheal reaction, and strong blue photoluminescence was observed even with the naked eye when these compounds were excited by a UV lamp. All of these compounds were not oxidated at all. Studies on the molecular structure showed that N → Si coordination bonds existed in these compounds, and those N → Si bonds caused the aggregation of carbonyl groups which show the strong luminescence.

A multifunctional silicon-containing hyperbranched epoxy: controlled synthesis, toughening bismaleimide and fluorescent properties

“…[37][38][39] From the traditional point of view, chromogenfree compounds rarely exhibit strong fluorescence; a few exceptions, however, have been covered recently, and they are those possessing dendritic or hyperbranched architecture, such as poly(amidoamine) (PAMAM), [40][41][42][43] polyureas (PURE), 44 hyperbranched phosphate (HBPP), 45 poly(ether amide)s (PEA), 46 poly-(propyleneimine) (PPI) 47 and poly(amino ester) (PAE). 52 We also reported new watersoluble hyperbranched polysiloxanes (WHPSs) contemporaneously bearing hydroxyl and primary amine groups, and the result shows that the terminal hydroxyl group rather than primary amine group in WHPSs plays a critical role in producing the blue-luminescent species. It is well recognized that the oxidation or acidification of the tertiary amine in PAMAM, PURE, PEA, PPI, PAE, PVP and PEI should lie behind the light emission.…”

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.…”

“…[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. Recently,t he clustering-triggered emission( CTE) mechanism, namely,c lustering of these nonconventional chromophores and subsequent electron overlap to form extended conjugation, were proposed by Yuan and Zhang [8, 14b] to rationalize the unique emission.…”

“…[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.…”