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A Series of Ultra-Efficient Blue Borane Fluorophores

Lookup NU author(s): Emeritus Professor Bill Clegg, Dr Paul Waddell

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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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Abstract

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.


Publication metadata

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

Year: 2020

Volume: 59

Issue: 23

Pages: 17058-17070

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

URL: https://doi.org/10.1021/acs.inorgchem.0c02277

DOI: 10.1021/acs.inorgchem.0c02277


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