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

Abstract

Two novel styrene-containing meta-carborane derivatives substituted at the second carbon cluster atom (C) with either a methyl (Me) or a phenyl (Ph) group are introduced herein along with a new set of stilbene-containing ortho- (o-) and meta- (m-) carborane dyads. The latter set of compounds have been prepared from styrene-containing carborane derivatives via a Heck coupling reaction. High regioselectivity has been achieved for these compounds by using a combination of palladium complexes [Pd(dba)]/[Pd(t-BuP)] as a catalytic system, yielding exclusively E isomers. All compounds have been fully characterised and the crystal structures of seven of them were analysed by X-ray diffraction. The absorption spectra of these compounds are similar to those of their respective fluorophore groups (styrene or stilbene), showing a very small influence of the substituent (Me or Ph) linked to the second C 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 C in o-carboranes. In contrast, all the m-carborane derivatives display similar photoluminescence (PL) behavior regardless of the substituent attached to the second C, demonstrating its small influence on emission properties. Additionally, m-carborane derivatives are significantly more fluorescent than their o-counterparts, reaching quantum yield values as high as 30.2%. Regarding solid state emission, only stilbene-containing Ph-o-carborane derivatives, which showed very low fluorescence in solution, exhibited notable PL emission in films attributed to 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 it is proved that it is possible to tailor the PL properties of carborane-stilbene dyads by changing the C substituent and the carborane isomer.

Photoluminescence in m-carborane–anthracene triads: a combined experimental and computational study

“…But more interestingly, the fluorescence efficiency can be tailored by changing the substituent at the adjacent Cc position, which may cause either an enhancement of the emission quantum yield or a total fluorescence quenching in the case of aromatic substituents. [11][12][13][65][66][67][68][69] Anthracene is a very well-studied -conjugate system easy to functionalize and with remarkable intrinsic photophysical, photochemical and chemical properties, which make it and its derivatives ideal molecules to construct fluorophores, fluorescent probes, organic light-emitting transistors, among others. 70,71 Throughout the last years, some carboranyl-functionalized anthracene derivatives have been reported and their photoluminescence behaviour explored.…”

Carborane‐BODIPY Dyads: New Photoluminescent Materials through an Efficient Heck Coupling

“…The 11 B{ 1 H} NMR spectra of all the compounds exhibit a triplet attributed to the ‐BF 2 unit, centered at 0.61 ppm for the aza‐BODIPYs and at 0.45 ppm for BODIPY derivatives. In addition to the ‐BF 2 resonance, those compounds bearing o ‐carborane clusters show the typical 1:1:8 or 2:8 distribution, whereas for m ‐isomers the pattern was 1:1:6:2 or 2:6:2, all of them being in the region from −3.63 to −13.70 ppm . The 13 C{ 1 H} NMR spectra of all the compounds show a resonance in the range of 41.0–43.0 ppm attributed to the benzylic carbon, and also for the Me‐carborane derivatives, the C c − C H 3 can be identified from 23.0–25.0 ppm.…”

Modulation of the cis‐ and trans‐Conformations in Bis‐o‐carborane Substituted Benzodithiophenes and Emission Enhancement Effect on Luminescent Efficiency by Solidification

“…Even though intense luminescence can be observed in the solution state, optical properties were often spoiled through ACQ by intermolecular interactions in the solid state. [5][6][7] It has been reported that some of the o-carborane [8][9][10][11][12][13] derivatives presented AIE [14][15][16][17][18][19][20][21] and can be applied as a solid-state luminescent material. [1][2][3] Intense solid-state luminescent properties originating from AIE were found and applied for developing the conjugated materials, including polymers.…”