Luminescent Blooming of Dendronic Carbon Nanotubes through Ion-Pairing Interactions with an EuIII Complex

L. Maggini, F. M. Toma, L. Feruglio, J. M. Malicka, T. Da Ros, N. Armaroli, M. Prato, D. Bonifazi,
Chem. – Eur. J. 2012, 18, 5889-5897, S5889/5881-S5889/5819
DOI: 10.1002/chem.201200237


A multiwalled carbon nanotube (MWCNT) scaffold was covalently functionalized with a second-generation polyamidoamine (PAMAM) dendron, presenting four terminal amino groups per grafted aryl moiety. These reactive functions were alkylated to obtain a positively charged polycationic dendron/carbon nanotube system (d-MWCNTs⋅Cl), which eventually underwent anion exchange reaction with a negatively charged and highly luminescent EuIII complex ([EuL4]⋅NEt4, in which L=(2-naphtoyltrifluoroacetonate)). This process afforded the target material d-MWCNTs⋅[EuL4], in which MWCNTs are combined with red-emitting EuIII centers through electrostatic interactions with the dendronic branches. Characterization of the novel MWCNT materials was accomplished by means of TGA and TEM, whereas d-MWCNTs⋅Cl and d-MWCNTs⋅[EuL4] further underwent XPS, SEM and Raman analyses. These studies demonstrate the integrity of the luminescent [EuL4] center in the luminescent hybrid, the massive load of the cationic binding sites, and the virtually complete anion-exchange into the final hybrid material. The occurrence of the ion-pairing interaction with MWCNTs was unambiguously demonstrated through DOSY NMR diffusion studies. Photophysical investigations show that MWCNTs⋅[EuL4] is a highly soluble and brightly luminescent red hybrid material in which MWCNTs act as photochemically inert scaffolds with negligible UV/Vis absorption, compared with the grafted Eu complex, and with no quenching activity. The high dispersibility of MWCNTs⋅[EuL4] in a polymer matrix makes it a promising luminophore for applications in material science.

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