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Royal Society of Chemistry, Dalton Transactions, 7(46), p. 2091-2104

DOI: 10.1039/c6dt04003a

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Carborane–stilbene dyads: the influence of substituents and cluster isomers on photoluminescence properties

This paper is available in a repository.
This paper is available in a repository.

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Abstract

Two novel styrene-containing meta-carborane derivatives substituted at the second carbon cluster atom (Cc) with either a methyl (Me), or a phenyl (Ph) group, are introduced herein alongside with a new set of stilbene-containing ortho- (o-) and meta- (m-) carborane dyads. The latter set of compounds has been prepared from styrenecontaining carborane derivatives via Heck coupling reaction. High regioselectivity has been achieved for these compounds by using a combination of palladium complexes [Pd2(dba)3]/[Pd(t-Bu3P)2] as a catalytic system, yielding exclusively E isomers. All compounds have been fully characterized and the crystal structures of seven of them analyzed by X-ray diffraction. The absorption spectra of these compounds are similar to those of their respective fluorophore groups (styrene or stilbene), showing very low influence of the substituent (Me or Ph) linked to the second Cc atom or the cluster isomer (o- or m-). On the other hand, fluorescence spectroscopy revealed high emission intensities for Me-o-carborane derivatives, whereas their Ph-o-carborane analogues evidenced an almost total lack of fluorescence, confirming the significant role of the substituent bound to the adjacent Cc in o-carboranes. In contrast, all the m-carborane derivatives display similar photoluminescence (PL) behavior regardless of the substituent attached to the second Cc, demonstrating its small influence on the emission properties. Additionally, m-carborane derivatives are significantly more fluorescent than their o- counterparts, reaching quantum yield values as high as 30.2%. Regarding the solid state emission, only stilbene-containing Ph-o-carborane derivatives, which showed very low fluorescence in solution, exhibited a notable PL emission in films attributed to the aggregation-induced emission. DFT calculations were performed to successfully complement the photoluminescence studies, supporting the experimentally observed photophysical behavior of the styrene and stilbene-containing carborane derivatives. In conclusion, in this work is proved that it is possible to tailor the PL properties of the carborane-stilbene dyads by changing the Cc substituent and the carborane isomer. ; This work has been supported by Ministerio de Economía y Competitividad, MINECO, (CTQ2013-44670-R and CTQ2013-41339-P), and Generalitat de Catalunya (2014/SGR/149). Theoretical calculations have been achieved using computers from the Centro Técnico de Informática del Consejo Superior de Investigaciones Ciéntificas (CTI-CSIC). ICMAB acknowledges financial support from the MINECO, through the “Severo Ochoa” Program for Centers of Excellence in R&D (SEV- 2015-0496). ; Peer reviewed