Click Synthesis and Properties of Carborane-Appended Large Dendrimers

Large dendrimers, noted G(n)-3-3(n+2)cage, containing 3(n+2) o-carborane cluster cages MeC2B10H10 at their peripheries (n = number of generation noted G(n)) have been synthesized by Huisgen-type azide alkyne Cu-1-catalyzed dipolar click cycloaddition reactions (CuAAC) between an o-carborane monomeric cluster containing an ethynyl group and arene-centered azido-terminated dendrimers G(n)-3(n+2)N(3) of generations 0, 1, and 2. Attempts to synthesize higher-generation dendrimers of this family yielded insoluble materials. The carborane dendrimers G(0)-9cage, G(1)-27cage, and G(2)-81cage have been characterized by H-1, C-13, B-11 NMR, elemental analysis, matrix-assisted laser desorption/ionization time of Flight (MALDI-TOF) mass spectroscopy, and size exclusion chromatography (SEC) showing low polydispersities, dynamic light scattering (DLS) showing hydrodynamic diameters of 5.7 nm for the G(1)-27cage and the 12.9 nm for the G(2)-81 cage. These dendrimers are extremely robust thermally, with 10% mass loss temperatures of 411 degrees C for the G(0)-9cage, 371 degrees C for the G(1)-27cage, and 392 degrees C for the G(2)-81cage. They all showed a strong absorption in the UV region peaking at 258 nm, whereas emission spectra of low intensities were observed between 280 and 480 nm.