High boron content carboranyl-functionalized aryl ether derivatives displaying photoluminescent properties

Abstract

The reaction of alpha,alpha'-bis(3,5-bis(bromomethyl)phenoxy-p-xylene (3) with 4 equiv of the monolithium salt of 1-Ph-1,2-C2B10H11 or 1-Me-1,2-C2B10H11 gave the corresponding neutral carboranyl-functionalized aryl ether derivatives closo-4 and closo-5, respectively. These compounds contain four closo clusters that were degraded using basic conditions with KOH in EtOH, affording the corresponding nido-6 and nido-7 as potassium salts. Nido species were also isolated with tetramethylammonium as cation giving compounds nido-8 and nido-9 in good yield. The potassium salts showed good solubility in water and polar solvents. All these compounds were characterized by 1H, 11B and 13C NMR spectroscopy and UV-vis. The electronic data in different solvents indicated a solvatochromic shift for all compounds and a red shift of the absorption maxima for the nido species with respect to the closo derivatives. These neutral and anionic carboranyl-functionalized aryl ether derivatives represent a new family of high boron content luminescent compounds that show strong fluorescence emission in different solvents at room temperature. This phenomenon is very interesting considering the fact that none of the precursors have such a property. The fluorescence emission depends on the cluster substituent (Ph or Me) and the solvent polarity. Additionally, the fluorescence emission intensity was clearly dependent on the solvent polarity; the closo species showed strongest fluorescence intensities in the non-polar solvents, while anionic species were highly emissive in polar solvents.

Synthesis and Characterization of New Fluorescent Styrene‐Containing Carborane Derivatives: The Singular Quenching Role of a Phenyl Substituent

“…To our knowledge, the first example of fluorescent molecules bearing ocarboranyl fragments was reported by our group in 2007. [15] Therein, we described the synthesis of high-boron-content neutral and anionic carboranyl-functionalized aryl ether derivatives that exhibited fluorescence emission in different solvents at room temperature. We proposed that specific interactions between the organic substituents and the cluster induce changes in the electronic structure of the molecule, which induces the luminiscence.…”

Substituent Effects on the Fluorescence Properties of ortho‐Carbor­anes: Unusual Emission Behaviour in C‐(2′‐Pyridyl)‐ortho‐carboranes

“…However, the vast majority of these compounds give very weak emissions; thus, these carboranes are considered (and have been reported for 4, [30] 7, [30] 12 [44] and 16 [20] ) as non-emissive. The influence of the substituents, Me, SH, SMe and SiMe 3 , on the photophysics of ortho-carborane is subtle, whereas the influence of the aryl groups, Ph, PPh 2 and 2′-pyridyl, is inevitably present with π-π* transitions and/or charge-transfer emissions.…”

“…[7][8][9][10][11][12][13][15][16][17][18][19][20][21][22][23][24][25][26][27][28] Dual fluorescence with CT and local transitions has been observed in some orthocarboranes. [12,13,[15][16][17][18][19][20]28] The ortho-carborane unit plays a role similar to meta-and para-carborane clusters in the photophysical process of a compound if there is a stronger electron acceptor than the cluster in these systems, [5,6,29,30] and if the ortho-carborane group is connected to a donor at one or more boron cluster atoms. [7,28,31] The ortho-carborane group is a much weaker electron acceptor when bonded at the boron atom (it may even be a donor depending on the position of the attached boron atom).…”

“…[46] Given that there have been many articles on the observed luminescence of 1-monoalkyl-, 1-monoaryl-and 1,2-diaryl-ortho-carborane derivatives, [7][8][9][10][11][12][13][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] by contrast 1-monomethyl-ortho-carborane 4, 1-monophenyl-ortho-carborane 7 and 1,2-diphenyl-ortho-carborane 16 were quoted to be non-emissive. [20,30] …”

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

“…Since our seminal work in 2007, in which the first example of fluorescent molecules containing carboranyl moieties was reported, our group, and others have developed new fluorescent materials incorporating carboranes. As a result, the interest in studying the photoluminescent (PL) properties of these compounds in view of new applications has noticeably increased.…”