Luminescent blooming of dendronic carbon nanotubes through ion-pairing interactions with an Eu III complex

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.