Emission via Aggregation of Alternating Polymers with o-Carborane and p-Phenylene−Ethynylene Sequences

Synthesis, Photophysical and Electronic Properties of a D-π-A Julolidine-Like Pyrenyl-o-Carborane

We synthesized 2-(1-1,2-dicarbadodecaboranyl(12))-6,6,12,12-tetramethyl-7,8,11,12-tetrahydro-6H,10H-phenaleno[1,9-fg]pyrido[3,2,1-ij]quinoline (4), a julolidine-like pyrenyl-o-carborane, with pyrene substituted at the 2,7-positions on the HOMO/LUMO nodal plane. Using solid state molecular structures, photophysical data, cyclic voltammetry, DFT and LR-TDDFT calculations, we compare o-carborane and B(Mes)2 (Mes=2,4,6-Me3C6H2) as acceptor groups. Whereas the π-acceptor strength of B(Mes)2 is sufficient to drop the pyrene LUMO+1 below the LUMO, the carborane does not do this. We confirm the π-donor strength of the julolidine-like moiety, however, which raises the pyrene HOMO-1 above the HOMO. In contrast to the analogous pyrene-2-yl-o-carborane, 2-(1-1,2-dicarbadodecaboranyl(12))-pyrene VI, which exhibits dual fluorescence, because the rate of internal conversion between locally-excited (LE) and charge transfer (CT) (from the pyrene to the carborane) states is faster than the radiative decay rate, leading to a thermodynamic equilibrium between the 2 states, 4 shows only single fluorescence, as the CT state involving the carborane as the acceptor moiety in not kinetically accessible, so a more localized CT emission involving the julolidine-like pyrene moiety is observed.

Solid-state excimer emission of o-carborane derivatives and applications for stimuli-responsive luminescent materials

o-Carborane is an icosahedral cluster containing boron and has been paid attention as a versatile platform for constructing stimuli-responsive materials with solid-state luminescence properties by suppressing aggregation-caused quenching (ACQ), which is the emission annihilation process observed in condensed states, such as concentrated solutions, solids and films. Non-specific intermolecular interactions in the condensed states resulting in ACQ are disturbed by the spherical boron cluster. More recently, it has been demonstrated from several reports that o-carborane is capable of assisting solid-state excimer emission in aryl-modified o-carboranes. Moreover, some of these materials provide unique stimuli-responsiveness. In the commodity design for solid-state luminescent materials, o-carboranes are responsible for disturbing intermolecular interactions and subsequently presenting solid-state luminescence. On the other hand, excimer emission, which is inducible from the intermolecular photophysical process, has been discovered in the solid state based on o-carborane materials. In this manuscript, recent progress in stimuli-responsive luminescent materials via excimer formation will be described. Moreover, as the further potential of o-carborane materials, recent findings on the photo-salient effect which can be induced through excimer formation followed by photoreaction will also be explained.

A Conjugated Carboranyl Main Chain Polymer with Aggregation-Induced Emission in the Near-Infrared

Materials exhibiting aggregation-induced emission (AIE) are both highly emissive in the solid state and prompt a strongly red-shifted emission and should therefore pose as good candidates toward emerging near-infrared (NIR) applications of organic semiconductors (OSCs). Despite this, very few AIE materials have been reported with significant emissivity past 700 nm. In this work, we elucidate the potential of ortho-carborane as an AIE-active component in the design of NIR-emitting OSCs. By incorporating ortho-carborane in the backbone of a conjugated polymer, a remarkable solid-state photoluminescence quantum yield of 13.4% is achieved, with a photoluminescence maximum of 734 nm. In contrast, the corresponding para and meta isomers exhibited aggregation-caused quenching. The materials are demonstrated for electronic applications through the fabrication of nondoped polymer light-emitting diodes. Devices employing the ortho isomer achieved nearly pure NIR emission, with 86% of emission at wavelengths longer than 700 nm and an electroluminescence maximum at 761 nm, producing a significant light output of 1.37 W sr-1 m-2.

The Photosalient Effect and Thermochromic Luminescence Based on o-Carborane-Assisted π-Stacking in the Crystalline State

Herein, we report the unique multiple-stimuli responsiveness of anthracene-tethered o-carborane derivatives. We designed and synthesized anthracene derivatives with different substitution positions and numbers of the o-carborane units. Two compounds had characteristic crystal structures involving the columnar π-stacking structures of the anthracene units. From the analysis of crystalline-state structure-property relationships, it was revealed that the crystals exhibited the photosalient effect accompanied by photochemical [4+4] cycloaddition reactions and temperature-dependent photophysical dual-emission properties including excimer emission of anthracene. Those properties were considered as non-radiative and radiative deactivation pathways through the excimer formation in the excited state and the formation of excimer species was facilitated by the π-stacking structure of anthracene units. Moreover, we found unusual temperature dependency on the occurrence of the photosalient effect. According to the data from variable temperature X-ray crystallography, a strong correlation between lattice shrinkage and strain accumulation is suggested.

Lanthanide complexes with a new luminescent iminophosphonamide ligand bearing phenylbenzothiazole substituents

A new iminophosphonamine Ph2P(HNPbt)(NPbt) (1, HL) bearing chromophore 2-(phen-2'-yl)-1,3-benzothiazole (Pbt) substituents was synthesized and introduced into lanthanide complexes. It was found that salt metathesis reactions between KL (2) generated in situ and LnCl3 lead to the formation of tris-iminophosphonamide complexes [LnL2]L (Ln = Y (3), Sm (4), Gd (5), Dy (6)), regardless of the 2/LnCl3 ratio. Compounds 3-6 consist of a cationic fragment [LnL2]+, where the lanthanide atom is surrounded by two rigidly κ4-coordinated ligands, and an L- anion residing in the outer coordination sphere. Iminophosphonamine 1 shows a rare excitation wavelength-dependent two-band luminescence in the solid state. For compounds containing the deprotonated form, namely potassium salt KL and complexes of Gd and Dy, a single-band luminescence with the color changing from turquoise to orange was observed. The Sm complex reveals a set of a few narrow well-resolved bands corresponding to the f-f transitions against the background of the outer-sphere ligand's emission.

Aggregation-induced emission from optically active X-shaped molecules based on planar chiral [2.2]paracyclophane

An optically active π-stacked molecule was synthesized incorporating planar chiral [2.2]paracyclophane and o-carborane units to impart circularly polarized luminescence and aggregation-induced emission properties to the molecule. The molecule exhibited a strong emission from the aggregated state in a mixed solvent system (H2O/THF) and the solid state in the PMMA matrix. In the aggregated state, weak circularly polarized luminescence was observed owing to the random intermolecular orientation. On the other hand, the circularly polarized luminescence was clearly observed in the PMMA film containing 1 wt% molecule. Theoretical studies using time-dependent density functional theory reproduced the molecule's circular dichroism and circularly polarized luminescence properties.

Revisiting the Role of Charge Transfer in the Emission Properties of Carborane-Fluorophore Systems: A TDDFT Investigation

In this study, we performed a detailed investigation of the S1 potential energy surface (PES) of o-carborane-anthracene (o-CB-Ant) with respect to the C-C bond length on o-CB and the dihedral angle between o-CB and Ant moieties. The effects of different substituents (F, Cl, CN, and OH) on carbon- or boron-substituted o-CB, along with a π-extended acene-based fluorophore, pentacene, on the nature and energetics of S1 → S0 transitions are evaluated. Our results show the presence of a non-emissive S1 state with an almost pure charge transfer (CT) character for all systems as a result of significant C-C bond elongation (C-C = 2.50-2.56 Å) on o-CB. In the case of unsubstituted o-CB-Ant, the adiabatic energy of this CT state corresponds to the global minimum on the S1 PES, which suggests that the CT state could be involved in emission quenching. Despite large deformations on the o-CB geometry, predicted energy barriers are quite reasonable (0.3-0.4 eV), and the C-C bond elongation can even occur without a noticeable energy penalty for certain conformations. With substitution, it is shown that the dark CT state becomes even more energetically favorable when the substituent shows -M effects (e.g., -CN), whereas substituents showing +M effects (e.g., -OH) can result in an energy increase for the CT state, especially for partially stretched C-C bond lengths. It is also shown that the relative energy of the CT state on the PES depends strongly on the LUMO level of the fluorophore as this state is found to be energetically less favorable compared to other conformations when anthracene is replaced with π-extended pentacene. To our knowledge, this study shows a unique example of a detailed theoretical analysis on the PES of the S1 state in o-CB-fluorophore systems with respect to substituents or fluorophore energy levels. Our findings could guide future experimental work in emissive o-CB-fluorophore systems and their sensing/optoelectronic applications.

Self-assembled organic and hybrid materials derived from oligo-(p-phenyleneethynylenes)

Oligo-(p-Phenyleneethynylenes) (OPEs) have garnered widespread interest over the past three decades due to their excellent opto-electronic properties. However, the chief focus has been on the use of mainly small molecules or polymeric systems for the study of their structural diversity in opto-electronic applications. Recently, researchers have started delving deeper into their utility in material applications. Purely organic materials such as supramolecular polymers, self-assembled nanostructures, nanostructured organogels and single-crystalline materials derived from OPEs have already been developed and researched. Chirality has also been introduced into these systems. Additionally, these have shown physical properties such as polymorphism, liquid crystallinity, melt formation, mechanochromism, etc. All these materials have also shown excellent luminescence properties with high quantum yield and some have even shown energy harvesting properties. There have also been sporadic reports on OPE linker based hybrid systems such as metallogels and metal-organic framework (MOF) structures where structural analysis reveals the origin of tunable emission in these materials. Furthermore, by innovative structural design, unexplored properties of OPEs such as water repellency, bioimaging, drug delivery, photocatalysis, energy transfer, nanomorphology control, photoconductivity, and colour tunability could be achieved. This feature article will, therefore, encompass a detailed discussion on the development of this field as well as the analysis of the properties realized in OPE derived self-assembled supramolecular materials. The main focus will be on the following classes of materials: soft supramolecular materials, crystalline supramolecular π-systems, nanoscale metal-organic frameworks (NMOFs) and bulk metal-organic frameworks (MOFs) and how their application horizon has been expanded by integrating OPEs into their structures.

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...

Unconventional Conjugation in macromonomers and polymers

Multiple reviews have been written concerning conjugated macromonomers and polymers both as general descriptions and for specific applications. In most examples, conjugation occurs via elec-tronic communication via continuous overlap of...

Resonance-Enhanced Two-Photon Absorption and Optical Power Limiting Properties of Three-Dimensional Perylene Bisimide Derivatives

Push-pull organic structures characterized by an intramolecular charge transfer (ICT) process and π-electron delocalization are potentially interesting luminescent materials. A series of three-dimensional o-carborane-containing perylene bisimide derivatives (PBIs) were synthesized, and their optical properties were systematically investigated to illustrate the stereo effect, especially on the two-photon absorption (2PA) and optical power limiting (OPL) properties. Open-aperture Z-scan curves showed that all four PBIs displayed strong and broad two-photon absorptivities based on the resonance-enhanced phenomenon. The maximum degenerate two-photon absorption cross section (δ_2PA) increased with the number of PBI substituents. The derivative CB-PBI possessed a δ_2PA value of ∼2400 GM at 650 nm, a significant enhancement in comparison with that of the parent PBI (∼719 GM), ascribed to the present stereo effect. When the aromatic-donating units changed from naphthyl and pyrenyl to PBI, the generated multidimensional intramolecular charge transfer (ICT) from the aromatic units to the o-carborane cage contributed to the 2PA processes. All of the fluorophores exhibited excellent optical power limiting (OPL) performances as well as a minimum limiting threshold of ∼4.98 mJ/cm² for CB-PBI. These significant results not only allow us to get deep insight into the nature of the fundamental stereo effect and nonlinear optical (NLO) response involved but also guide us toward the design of new multifunctional luminescent materials.

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.

Flexible and Transparent Oligothiophene-o-Carborane-Containing Hybrid Films for Nonlinear Optical Limiting Based on Efficient Two-Photon Absorption

Structure-property relationship for fluorophores with favorable nonlinear optical (NLO) properties are promising topics in organic chemistry and material science. Herein, a series of terthiophene-o-carborane dyads and triads covalently linked with different end-capping styles were readily synthesized and comprehensively investigated. Quantitative values of the crystal and packing structures, photophysical parameters including aggregation-induced emission (AIE) and two-photon absorption (2PA) were provided. Significant impact of carborane unit for introducing the AIE characteristic has been investigated in contrast to the parent oligothiophene. All the obtained fluorophores exhibit maximum absorption around 370 nm in THF and emit bright reddish photoluminscence with absolute fluorescence quantum yields above 16% in solid states. Intramolecular charge communication between oligothiophene and carborane plays important roles in the related NLO properties. These results are supported well by the time-dependent DFT theoretical calculations. Effective 2PA cross sections (δ_2PA = 95-355 GM@650 nm) and transition dipole moments of the derivatives are variable for different end-capping styles. Their potential applications as optical limiting materials based on the 2PA mechanism in solutions and doped PDMS films were further evaluated. Taken together, this work provides an understanding of their structure-property relationship, and flexible PDMS films as outstanding candidates for practical applications in optical limiting.

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.

Recovering the Thermally Activated Delayed Fluorescence in Aggregation-Induced Emitters of Carborane

The aggregation-induced emission (AIE) behaviors of carborane-based hybrid emitters have been extensively reported, while their combinations with the thermally activated delayed fluorescence (TADF) are still scarce. We designed and synthesized three Janus carboranes (the chemical structures resemble the double-faced god, Janus) Cb-1/2/3 with different carbazole moieties. All of the Janus carboranes exhibited quenched emission in solution with Φ_PL (quantum efficiency of photoluminescence (PL)) lower than 0.01. The PL performance was improved by proceeding to the aggregates in THF/water (Φ_PL 0.17-0.35) and further improved in the crystals or solid with Φ_PL up to 0.99 for Cb-1, 0.85 for Cb-2, and 0.61 for Cb-3, which agreed with the AIE enhancement. Although the PL of solid Cb-1/2/3 showed non-TADF properties with lifetimes only at several nanoseconds, the crystallographic studies have shown a root cause of π···π stacking that quenched the TADF, and the theoretical calculations forecasted small singlet-triplet energy gaps (ΔE_S-T) therein. According to these findings, TADF was recovered in Cb-1/2/3 by doping into 1,3-bis(carbazol-9-yl)benzene (mCP). The 10 wt % doped films of Cb-1/2/3 have achieved a trade-off of Φ_PL (0.84 in Cb-3 and 0.83 in Cb-1) and delayed lifetime (up to 8 μs). The doped devices of organic light-emitting diodes incorporating Cb-1/2/3 achieved the highest external quantum efficiency at 10.1% and the maximized luminance of 5920 cd/m² at a driving voltage of 8 V.

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.

Supramolecular architectures sustained by delocalised C–I⋯π(arene) interactions in molecular crystals and the propensity of their formation

A survey of delocalised C–I⋯π(chelate ring) interactions is presented.

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.

Experimental proof for emission annihilation through bond elongation at the carbon-carbon bond in o-carborane with fused biphenyl-substituted compounds

Because of their unique luminescence properties, such as aggregation-induced emission (AIE), intense solid-state luminescence and stimuli-responsive luminochromism, aryl-substituted o-carboranes have attracted attention as a platform for developing functional optoelectronic materials. However, there still remains one fundamental issue with the detailed mechanism of solution quenching in AIE behaviors. Aryl-modified o-carboranes with AIE properties exhibit intense emission not in solution but in the solid state. According to quantum calculations and many experimental results, the elongation at the carbon-carbon bond in o-carborane in the excited state, followed by nonradiative decay, has been proposed as a main path for emission annihilation in solution. However, intramolecular rotation would simultaneously occur, and there is a possibility that emission annihilation could be induced by the combination of both bond elongation and rotation. In this study, we designed two types of biphenyl-substituted o-carboranes having fused structures at the neighbor carbon and boron atoms for fixing molecular conformation. In these molecules, bond elongation is allowed, while rotation would be prohibited. From the series of optical measurements and theoretical investigations, we proved that emission annihilation can occur through bond elongation in the absence of rotation. Moreover, we show that bond elongation could be suppressed by introducing a bulky substituent at the adjacent carbon, and emission color tuning was achieved. This is the first example, to the best of our knowledge, to prove that excitation decay can proceed only through bond elongation without electronic perturbation caused by rotation.

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.

A new type of carborane-based electron-accepting material

Direct attachment of the ethynyl group significantly affects the electrochemical properties of o-Cb systems.

Introducing borane clusters into polymeric frameworks: architecture, synthesis, and applications

This feature article summarizes the preparation and applications of borane cluster-containing polymers and covers research progress and future trends of borane cluster-containing linear, dendritic, macrocyclic polymers and metal–organic frameworks.

Emissive tetraphenylethylene (TPE) derivatives in a dissolved state tightly fastened by a short oligo(ethylene glycol) chain

The requirements for strong emission from a typical AIEgen in solution were quantitatively examined both by photochemical experiments and theoretical computations.

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.

Film-based fluorescence sensing: a "chemical nose" for nicotine

A novel series of emissive o-carborane derivatives, which showed multicolor, highly solid-state emission (ΦF ≥ 43%) and ideal photochemical stability, were synthesized. Inspired by the powerful mammalian olfactory system, we, for the first time, successfully obtained a fluorescent sensor array, which exhibits superior detection capability for nicotine in the gaseous phase (down to 3 ppb). Furthermore, the sensor array can be extended to detect nicotine in aqueous solution at the nano-gram level (∼0.1 ng cm-2) and determine the smoke of cigarette and electronic cigarette.

Synthesis and Characterization of Phosphorus- and Carborane-Containing Polyoxanorbornene Block Copolymers

Grubbs-catalyzed ring-opening metathesis polymerization (ROMP) of carborane- and phosphonate-containing monomers has been used for the generation of hybrid block copolymers. Molecular weights with Mn of 50,000 g/mol were readily obtained with polydispersity index values, Đ, between 1.03⁻1.08. Reaction of the phospha ester and carborane substituted oxanorbornene block copolymer with trimethylsilyl bromide led to a new polymer with phosphonic acid functionalities. In application studies, the phospha-carborane functionalized block polymer was tested as heat resistance material. Thermal stability was investigated by thermal gravimetric analysis (TGA) and microscale combustion calorimetry (MCC) analysis. Thermal treatment and ceramic yield under air were directly correlated to the carborane content of the block copolymer. However, phosphorus content in the polymer was more crucial for the char residues when heated under nitrogen atmosphere. The peak heat release rate (PHRR) increased as the number of phosphonate functionalities increased. However, corresponding phosphonic acid derivatives featured a lower heat release rate and total heat release. Moreover, the phosphonic acid functionalities of the block copolymer offer efficient chelating capabilities for iron nanoparticles, which is of interest for applications in biomedicine in the future. The complexation with iron oxide nanoparticles was studied by transmission electron microscopy (TEM) and inductively coupled plasma mass spectrometry (ICP⁻MS).

Consideration of Molecular Structure in the Excited State to Design New Luminogens with Aggregation-Induced Emission

Aggregation-induced emission (AIE) is a photoluminescence phenomenon in which an AIE luminogen (AIEgen) exhibits intense emission in the aggregated or solid state but only weak or no emission in the solution state. Understanding the mechanism of AIE requires consideration of excited state molecular geometry (for example, a π twist). This Minireview examines the history of AIEgens with a focus on the representative AIEgen, tetraphenylethylene (TPE). The mechanisms of solution-state quenching are reviewed and the crucial role of excited-state molecular transformations for AIE is discussed. Finally, recent progress in understanding the relationship between excited state molecular transformations and AIE is overviewed for a range of different AIEgens.

Synthesis of o-carborane-functionalized metal–organic frameworks through ligand exchanges for aggregation-induced emission in the solid state

o-Carborane-functionalized MOFs were successfully prepared through ligand exchanges, and the PL were drastically shifted by AIE in the solid state.

Aggregation-Induced Emission and White Luminescence from a Combination of π-Conjugated Donor-Acceptor Organic Luminogens

Two new star-shaped phenyl- and triazine-core based donor-acceptor (D-A) type conjugated molecules bearing triphenylamine end-capped arms were synthesized and characterized as imminent organic optoelectronic materials. Photophysical properties of the compounds were explored systematically via spectroscopic and theoretical methods. Because of the presence of donor-acceptor interactions, these luminogens display multifunctional properties, for instance, high extinction coefficient, large stokes shift, and pronounced solvatochromic effect. The compounds also exhibited phenomenon known as aggregation-induced emission on formation of nano-aggregates in the tetrahydrofuran-water mixture. The aggregate formation was confirmed by transmission electron microscopy, scanning electron microscopy, and dynamic light scattering analyses. Moreover, by controlling the electron withdrawing ability of the acceptor, complementary emissive fluorophores (blue and yellow) were achieved. These two complementary colors together span the entire range of visible spectrum (400-800 nm) and therefore when mixed in a requisite proportion generate white light in solution phase. These findings have potential for the progress of new organic white light radiating materials for applications in lighting and display devices.

Carborane-Induced Excimer Emission of Severely Twisted Bis-o-Carboranyl Chrysene

The synthesis of a highly twisted chrysene derivative incorporating two electron deficient o-carboranyl groups is reported. The molecule exhibits a complex, excitation-dependent photoluminescence, including aggregation-induced emission (AIE) with good quantum efficiency and an exceptionally long singlet excited state lifetime. Through a combination of detailed optical studies and theoretical calculations, the excited state species are identified, including an unusual excimer induced by the presence of o-carborane. This is the first time that o-carborane has been shown to induce excimer formation ab initio, as well as the first observation of excimer emission by a chrysene-based small molecule in solution. Bis-o-carboranyl chrysene is thus an initial member of a new family of o-carboranyl phenacenes exhibiting a novel architecture for highly-efficient multi-luminescent fluorophores.