Color-tuning and manipulation of aggregation-induced emission efficiency of o-carborane–tetraphenylethylene dyads through substituted o-carboranes

Two new carborane-containing tetraphenylethylene derivatives (1 and 2) were designed and synthesized. Together with our previously published compounds (3–5), we studied structure–activity relationships in detail. Results showed that compounds 1...

Theoretical Simulations of Thermochromic and Aggregation-Induced Emission Behaviors of a Series of Red-Light Anthracene-o-carborane Derivatives

Quantum mechanical and molecular dynamics simulations have been carried out on a series of anthracene-o-carborane derivatives (ANT-H, ANT-Ph, ANT-Me and ANT-TMS) with rare red-light emission in the solid state. The simulation of the heating process of the crystals and further comparison of the molecular structures and excited-state properties before and after heating help us to disclose the thermochromic behavior, that is, the red-shift emission is caused by elongation of the C1-C2 bond in the carborane moiety after heating. Thus, we believe that the molecular structure in the crystal is severely affected by heating. Transformation of the molecular conformation appears in the ANT-H crystal with increasing temperature. More specifically, the anthracene moiety moves from nearly parallel to the C1-C2 bond to nearly perpendicular, causing the short-wavelength emission to disappear after heating. As for the aggregation-induced emission phenomenon, the structures and photophysical properties were investigated comparatively in both the isolated and crystal states; the results suggested that the energy dissipation in crystal surroundings was greatly reduced through hindering structure relaxation from the excited to the ground state. We expect that discussion of the thermochromic behavior will provide a new analysis perspective for the molecular design of o-carborane derivatives.

Synthesis and Structure of an o-Carboranyl-Substituted Three-Coordinate Borane Radical Anion

Bis(1-(4-tolyl)-carboran-2-yl)-(4-tolyl)-borane [(1-(4-MeC6 H4 )-closo-1,2-C2 B10 H10 -2-)2 (4-MeC6 H4 )B] (1), a new bis(o-carboranyl)-(R)-borane was synthesised by lithiation of the o-carboranyl precursor and subsequent salt metathesis reaction with (4-tolyl)BBr2 . Cyclic voltammetry experiments on 1 show multiple distinct reduction events with a one-electron first reduction. In a selective reduction experiment the corresponding paramagnetic radical anion 1.- was isolated and characterized. Single-crystal structure analyses allow an in-depth comparison of 1, 1.- , their calculated geometries, and the S1 excited state of 1. Photophysical studies of 1 show a charge transfer (CT) emission with low quantum yield in solution but a strong increase in the solid state. TD-DFT calculations were used to identify transition-relevant orbitals.

Color-tunable and Highly Emissive Solid Materials Constructed from Tetraphenylethylene-o-carborane-based Building Blocks: Synthesis, Aggregation-induced emission, and Photophysics

A novel kind of expanded tetraphenylethylene (TPE)-carborane-TPE pentad has been synthesized by using two adjacent carborane moieties as central bridges and three TPE units in lateral positions. Its solid-state fluorescence quantum yield was substantially increased to 68.2% by expanding the number of bridges between carborane and TPE. Subsequently, the emission color shifted from blue to orange-yellow (126 nm). Mechanical insights into the electronic structure of the extended TPE-carborane-TPE pentads were obtained from density functional theory (DFT) calculations.

Highly Deformed o-Carborane Functionalised Non-linear Polycyclic Aromatics with Exceptionally Long C-C Bonds

The effect of substituting o-carborane into the most sterically hindered positions of phenanthrene and benzo(k)tetraphene is reported. Synthesised via a Bull-Hutchings-Quayle benzannulation, the crystal structures of these non-linear acenes exhibited the highest aromatic deformation parameters observed for any reported carborane compound to date, and among the largest carboranyl C-C bond length of all organo-substituted o-carboranes. Photoluminescence studies of these compounds demonstrated efficient intramolecular charge-transfer, leading to aggregation induced emission properties. Additionally, an unusual low-energy excimer was observed for the phenanthryl compound. These are two new members of the family of carborane-functionalised non-linear acenes, notable for their peculiar structures and multi-luminescent properties.

Reversibly Switchable Fluorescent Molecular Systems Based on Metallacarborane-Perylenediimide Conjugates

Icosahedral metallacarboranes are θ-shaped anionic molecules in which two icosahedra share one vertex that is a metal center. The most remarkable of these compounds is the anionic cobalt-based metallacarborane [Co(C₂ B₉ H₁₁ )₂ ]^- , whose oxidation-reduction processes occur via an outer sphere electron process. This, along with its low density negative charge, makes [Co(C₂ B₉ H₁₁ )₂ ]^- very appealing to participate in electron-transfer processes. In this work, [Co(C₂ B₉ H₁₁ )₂ ]^- is tethered to a perylenediimide dye to produce the first examples of switchable luminescent molecules and materials based on metallacarboranes. In particular, the electronic communication of [Co(C₂ B₉ H₁₁ )₂ ]^- with the appended chromophore unit in these compounds can be regulated upon application of redox stimuli, which allows the reversible modulation of the emitted fluorescence. As such, they behave as electrochemically-controlled fluorescent molecular switches in solution, which surpass the performance of previous systems based on conjugates of perylendiimides with ferrocene. Remarkably, they can form gels by treatment with appropriate mixtures of organic solvents, which result from the self-assembly of the cobaltabisdicarbollide-perylendiimide conjugates into 1D nanostructures. The interplay between dye π-stacking and metallacarborane electronic and steric interactions ultimately governs the supramolecular arrangement in these materials, which for one of the compounds prepared allows preserving the luminescent behavior in the gel state.

Configuration-controllable synthesis of Z/E isomers based on o-carborane-functionalized tetraphenylethene

Two Z/E isomers, namely, Z-TPE-2Car and E-TPE-2Car, with clear configuration were synthesized using an effective route and have high solid-state fluorescence quantum yields, reaching 99% and 90%, respectively.

Synthesis and photophysical properties of a new tetraphenylethylene-o-carborane-based star-shaped molecule

A novel TPE-o-carborane-based star-shaped molecule with a triphenylamine core was synthesized. In the solid state, the absolute luminescent quantum yield of this dendrimer can be improved to 62%.

Recent Progress in the Development of Solid-State Luminescent o-Carboranes with Stimuli Responsivity

o-Carborane, a cluster compound containing boron and adjacent carbon atoms, displays intriguing luminescent properties. Recently, compounds containing o-carborane units were found to show suppressed aggregation-induced quenching and intense solid-state emission; they also show potential for the development of stimuli-responsive luminochromic materials. In this Minireview, we introduce three kinds of fundamental photochemical properties: aggregation-induced emission, twisted intramolecular charge transfer in crystals, and environment-sensitive excimer formation in solids. Based on these properties, several types of luminochromism, such as thermos-, vapo-, and mechanochromism, have been discovered. Based mainly on results from recent studies, we illustrate these mechanisms as well as unique luminescent behaviors of o-carborane derivatives.

Aggregation-Induced Fluorescence of Carbazole and o-Carborane Based Organic Fluorophore

Carbazole based fluorophores 9-butyl-3,6-bis-(phenylethynyl)-9H-carbazole (1) and 9-butyl-3,6-bis-(2-phenyl-o-carborane)-9H-carbazole (2) were synthesized via Sonogashira type cross-coupling reaction and followed by insertion with decaborane. Compound 1 exhibited far more intense fluorescence than 2 in THF solution, while in solid state 2 exerted stronger fluorescence than 1. The fluorescence quenching behavior of 2 in THF solution could be attributed to the intramolecular charge transfer of donor-acceptor system in 2, which was confirmed by electrochemical experiments and DFT calculations. The fluorescence enhancement of 2 in solid state can be ascribed to aggregational induced packing which was evidenced by crystallographic study. In addition, compound 2 showed typical aggregation induced emission (AIE) behavior.

BODIPY–ortho-carborane–tetraphenylethylene triad: synthesis, characterization, and properties

Two new compounds, BODIPY–tetraphenylethylene dyad and BODIPY–o-carborane–tetraphenylethylene triad, were designed and synthesized.