Ortho‐Carborane‐Functionalized Luminescent Polyethylene: Potential Chemodosimeter for the Sensing of Nucleophilic Anions

Abstract

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...

Alteration of intramolecular electronic transition via deboronation of carbazole-based o-carboranyl compound and intriguing ‘turn-on’ emissive variation

“…The 1 H{ 11 B} and 13 C NMR spectra of closo-Cz displayed resonances corresponding to the 9methyl-9H-carbazole moiety. In particular, the broad singlet peaks in the region of 3.5-2.3 ppm in the 1 H{ 11 B} NMR spectrum (assigned to 10H atoms in total) conrmed the presence of the -BH groups of the o-carborane cage. In addition, two distinct signals observed at 88 and 86 ppm in the 13 C NMR spectrum were attributed to the carbon atoms in o-carborane.…”

“…Among the icosahedral boron-cluster compounds, closo-orthocarborane (1,2-dicarba-closo-dodecaborane) has recently attracted extensive attention as a functional moiety for applied materials in the elds of optoelectronic devices [1][2][3][4] and chemodosimeter/sensors [5][6][7][8][9][10][11][12][13][14][15][16][17] because o-carborane-appended p-aromatic uorophores can exhibit unique photophysical properties [2][3][4] and have reasonable thermal and electrochemical stabilities. [1][2][3]26,66 Such intriguing features arise from the strong electron withdrawing nature attributable to the carbon atoms of the cluster, which originates from the high polarisability of their s-aromaticity.…”

“…This conversion to nido-o-carborane induces a severe counter-current ICT transition since its electronic role in the dyad system changes to a donor (D) due to the anionic nature of the nido-species. [5][6][7][8][9][10][11][12][13][14][15][16][73][74][75][76] Indeed, the photophysical characteristics of closo-o-carborane appended onto various organic luminophores have been found to change dramatically during conversion to the nido-species in the presence of nucleophilic anions, suggesting its potential as a functional unit applicable to visualised sensory materials. [5][6][7][8][9][10][11][12][13][14][15][16] Thus, to further investigate such changes in photophysical properties via the conversion of closo-o-carborane to the anionic nido-o-species by deboronation with a nucleophilic anion, we strategically designed and prepared two carbazole-based o-carboranyl compounds, in which closo-or nido-o-carborane is appended to the C3-position of 9-methyl-9H-carbazole (closo-Cz and nido-Cz, respectively, Scheme 1).…”

Polythiophenes with vinylene linked ortho, meta and para-carborane sidechains

“…Some research has been carried out into the effects of pendant carborane cages on the properties of conjugated polymers, although to date the carboranes have either been connected via an alkyl chain linker, or directly fused to the conjugated backbone. [19][20][21][22][23][24][25][26][27][28][29][30] Hence polymers with pendant carborane units have been demonstrated to possess high stability in thermally-annealed films, a feature anticipated to be inherently useful for functional conjugated polymers whose applications are realised in the solid state. 18 Furthermore, polyfluorene derivatives incorporating silyl substituted ortho-carboranes, connected via an alkyl chain linker, have demonstrated enhanced solubility and suppressed aggregation (which in this instance was desirable), suggesting that the carborane cage may be effective at promoting polymer solubility.…”

Grant funds program to study advanced imaging

“…Recently, chemodosimeters have attracted considerable attention; however, a few polymeric chemodosimeters have been reported 31–34. For example, Swager's group31 reported a PPE‐based polymeric chemodosimeter for fluoride ions using fluoride triggered SiO bond cleavage; Wang's group32 reported a polymeric chemodosimeter for highly selective and sensitive detection of 2,4,6‐trinitrotoluene and picric acid based on donor–acceptor architecture.…”