Solid‐State Photochromism by Molecular Assembly of Bis‐o‐carboranyl Siloles

Abstract

A new type of solid‐state photochromism was observed in an AB2‐type molecular assembly comprising a central silole and two peripheral o‐carborane units, and in this assembly, depending on the assembling positions of those units at the adjoining benzene ring, two different regioisomers were formed: Si‐m‐Cb and Si‐p‐Cb. Each isomer showed different solid‐state photochromism depending on its solid‐state molecular conformation and was either in the crystalline or amorphous state. The crystals of each meta‐ or para‐isomer, CSi‐m‐Cb or CSi‐p‐Cb, showed yellow or blue emission, and mechanically grinding those crystals into amorphous powders of ASi‐m‐Cb and ASi‐p‐Cb, switched their emissions to blue and yellow, respectively. Photophysical studies revealed that the electronic interaction between silole and o‐carborane units determined the emission color. The crystal and DFT‐optimized structures each account for the crystalline and amorphous structures, respectively, and are correlated well with the electronic interactions in the molecular assembly in the solid state, thus enabling the prediction of the solid‐state molecular conformational change.

Reversibly Switchable Fluorescent Molecular Systems Based on Metallacarborane–Perylenediimide Conjugates

“…Given the previous reports on the improved emissive behavior of carborane‐fluorophore conjugates upon aggregation, [6,7c–j] we also investigated the optical properties of 1 and 2 in the solid state, which were compared to those of reference PDI dye 7 . As previously reported for thin films of symmetric perylenediimide fluorophores bearing branched alkyl side chains, [37] large differences were observed when optically characterizing 7 as a solid powder relative to solution.…”

“…The emission from these AIE‐active, CT‐based carborane‐emitter conjugates is sensitive to external stimuli that alter molecular packing (e.g. mechanical forces, temperature, chemical environment), and can be used for the preparation of smart materials [7c–j] . However, attempts to provide further functionality to these systems by reversibly switching the electronic communication between fluorophores and boron clusters have not been reported.…”

A comparison of para, meta, and ortho-carborane centred non-fullerene acceptors for organic solar cells

“…10–17 Such properties can be finely tuned through the choice of conjugated substituent groups, and may result in responsivity to external factors such as thermal or mechanical stimuli, or exposure to solvent vapours. 18–27 Emissive carborane species have also been demonstrated as the photoactive component in organic light emitting diodes on several occasions. 28–32…”

“…[10][11][12][13][14][15][16][17] Such properties can be finely tuned through the choice of conjugated substituent groups, and may result in responsivity to external factors such as thermal or mechanical stimuli, or exposure to solvent vapours. [18][19][20][21][22][23][24][25][26][27] Emissive carborane species have also been demonstrated as the photoactive component in organic light emitting diodes on several occasions. [28][29][30][31][32] Examples of emissive carborane-containing species also include a number of conjugated polymers, with emissive properties depending on the selection of carborane isomer and substituent site, and a certain tuneability based on the selection of conjugated co-monomers.…”

Ru(ii) and Ir(iii) phenanthroline-based photosensitisers bearingo-carborane: PDT agents with boron carriers for potential BNCT

“…[44][45][46][47] Additionally, due to their geometric and electronic nature, a groundbreaking field has emerged in the last decade related to electron-transfer or electron-promotion phenomena, including the realisation of photoluminescent boron cluster-bearing molecular materials. 48,49 In this regard, our group 35,[50][51][52][53][54][55] and others [56][57][58][59][60][61][62][63][64][65] have developed new fluorescent materials by linking carborane clusters to fluorescent π-conjugated organic systems. Carboranes have also demonstrated their effectiveness in tuning the phosphorescence properties when bonded to a ligand coordinated to heavy metal centre.…”