Closo-1,2-C 2 B 10 H 12 , so called ortho-carborane, is a wellknown icosahedral boron-cluster compound that possesses unique properties, such as a highly polarizable s-aromatic character, an electron-withdrawing nature, a high 10 B content, and a high thermal and chemical stability. [1] Owing to these interesting properties, compounds derived from orthocarborane have received a great deal of attention as promising materials in a wide range of applications, [2] such as catalysis, [3] hybrid materials, [4] optoelectronic materials, [5][6][7][8][9] doping agents in conducting polymers, [10] potentiometric sensors, [11] and boron-neutron-capture therapy (BNCT) [12] . Whilst a number of studies on the design and synthesis of ortho-carborane-based compounds have focused on small molecular systems, polymers bearing carborane moieties are recently attracting great interest because the incorporation of carborane moieties into a polymer backbone could lead to the modulation of the electronic and optical properties of the polymer. Although the majority of polymeric carboranes developed so far have been utilized in main-chain, conjugate polymers, [5,13] the development of side-chain polymers has rarely been reported; [6,14] this scarcity is in spite of various advantages of this type of polymer including the ability to control the polymer architecture in terms of molecular weight, functionality, and the degree of incorporation that may lead to intriguing properties.In this regard, polyolefins with pendant ortho-carboranemoieties can be considered as a novel class of such sidechain carboranyl polymers. As single-site catalytic systems based on Group 4 organometallic complexes have been an effective and straightforward method for the preparation of functionalized polyolefins, [15][16][17] it could be anticipated that the catalytic (co)polymerization of a-olefins bearing electron-deficient, bulky carborane groups may lead to the production of carboranyl polymers with well-defined structures. To this end, the copolymerization of ethylene with w-orthocarboranyl-a-olefin as a co-monomer using a [Me 2 TiCl 2 ] (CGC)/methylaluminoxane (MAO) catalytic system [18] was explored to develop a carboranefunctionalized polyethylene. In particular, it was found that the resulting polymer displayed not only photoluminescence under UV irradiation but also luminescence quenching in the presence of nucleophilic anions, thus revealing potential chemodosimetric sensing properties. Herein, the synthesis, characterization, and luminescent properties of polyethylene with side-chain ortho-methyl-carboranes are described.The ortho-carborane-substituted a-olefin, 1-methyl-2-(oct-7-en-1-yl)-closo-1,2-carborane (1) was employed as a co-monomer. Carborane 1 was prepared from the reaction of 8bromo-1-octene in the presence of a catalytic amount of lithium iodide [19] and the lithium salt generated in situ from 1-methyl-ortho-carborane and nBuLi in good yield after purification (70 %). The identity of 1 was confirmed by multinuclear NMR spectroscopy and mass...