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Lookup NU author(s): Emeritus Professor Bill CleggORCiD,
Dr Paul Waddell
This is the authors' accepted manuscript of an article that has been published in its final definitive form by American Chemical Society, 2020.
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We present the first examples of alkylated derivatives of the macropolyhedral boron hydride,anti-B18H22 – which is the gain medium in the first borane laser. This new series of ten highly-stableand colourless organic-inorganic hybrid clusters are capable of the conversion of UVA irradiation toblue light with fluorescence quantum yields of unity. This study gives a comprehensive description oftheir synthesis, isolation and structural characterization together with a delineation of theirphotophysical properties using a combined theoretical and experimental approach. Treatment of anti-B18H22 1 with RI (where R = Me or Et) in the presence of AlCl3 gives a series of alkylated derivatives,Rx-anti-B18H22-x (where x = 2 to 6), compounds 2-6, in which the 18-vertex octadecaborane clusterarchitectures are preserved and yet undergo a linear “polyhedral swelling”, depending on the numberof cluster alkyl substituents. The use of dichloromethane solvent in the synthetic procedure leads todichlorination of the borane cluster and increased alkylation to give Me11-anti-B18H9Cl2 11, Me12-anti-B18H8Cl2 12 and Me13-anti-B18H7Cl2 13. All new alkyl derivatives are highly stable, extremelyefficient (ΦF = 0.76 – 1.0) blue fluorophores (λems = 423 - 427 nm) and are soluble in a wide range oforganic solvents and also a polystyrene matrix. The Et4-anti-B18H18 derivative 4b crystallizes frompentane solution in two phases, with consequent multi-absorption and multi-emission photophysicalproperties. An ultra-fast transient UV-vis absorption spectroscopic study of compounds 4a and 4breveals that an efficient excited-state absorption at the emission wavelength inhibits the laserperformance of these otherwise remarkable luminescent molecules. All these new compounds add tothe growing portfolio of octadecaborane-based luminescent species, and, in an effort to broaden theperspective on their highly-emissive photophysical properties, we highlight emerging patterns in theinfluence that successive substitutions have on the molecular size of the 18-vertex borane clusterstructure and distribution of electron density within.
Author(s): Bould J, Lang K, Kirakci K, Cerdan L, Roca-Sanjuan D, Frances-Monerris A, Clegg W, Waddell PG, Fuciman M, Polivka T, Londesborough MGS
Publication type: Article
Publication status: Published
Journal: Inorganic Chemistry
Print publication date: 07/12/2020
Online publication date: 09/11/2020
Acceptance date: 22/10/2020
Date deposited: 27/10/2020
ISSN (print): 0020-1669
ISSN (electronic): 1520-510X
Publisher: American Chemical Society
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