Boron‐Cluster‐Enhanced Ultralong Organic Phosphorescence

Although carborane‐based luminescent materials have been studied for years, no persistent phosphor has been reported so far. Herein, we describe boron‐cluster‐based persistent phosphors obtained by linking a σ‐aromatic carboranyl cage to the π system of a carbazolyl group. The carboranes were found to promote intersystem crossing from a singlet to a triplet state. The rigid boron cluster was able to stabilize the ultralong triplet excitons through multiple nonclassical hydrogen bonds, such as B?H???π interactions, thus leading to a long lifetime of up to 0.666 s and an absolute phosphorescence quantum yield of 7.1 %, which is outstanding for an organic phosphor without heavy atoms. These phosphors can be excited by visible light and show dynamic emission behavior, including thermochromism and mechanochromism. This study demonstrates that non‐metal/heavy‐atom boron clusters can be used to develop multifunctional high‐performance phosphors for potential applications.     

Synthesis,Characterization, and Thermal Behavior of Carboranyl–Styrene Decorated Octasilsesquioxanes: Influence of the Carborane Clusters on Photoluminescence

Novel polyhedral oligomeric silsesquioxanes (POSS) or octasilsesquioxanes with carboranyl–styrene fragments attached to each corner are described. These compounds have been synthesized by olefin‐metathesis reactions between octavinylsilsesquioxane and carboranyl–styrene compounds that possess different substituents (Ph, Me, or H). In all cases, these reactions, which were catalyzed by the Grubbs catalyst, are highly regioselective and yield exclusively the E isomers. The existence of the carborane cage in the POSS structure induces a remarkable thermal stability in these compounds. After combustion at 1000 °C, these carboranyl–POSS compounds exhibit a mass loss lower than 10 %. The UV/Vis absorption data of these carboranyl–POSS compounds shows a slight bathochromic shift with respect to the carboranyl–styrene monomers, with an absorption maximum around 262 nm. Nevertheless, important differences in the emission spectra of the carboranyl–POSS compounds with regard to their carboranyl–styrene precursors are observed; the phenyl‐o‐carborane‐containing POSS compound exhibits the highest fluorescence intensity (Φ_F=44 %), whereas for the POSS compound bearing the methyl substituent, and for the unsubstituted o‐carborane clusters, the fluorescence intensity is much lower (Φ_F=9 and 2 %, respectively). This is precisely the reverse of what occurs with the monomers, in which the unsubstituted o‐carboranyl–styrene compound exhibits the highest Φ_F, and a quenching of the fluorescence is observed in the phenyl‐o‐carboranyl–styrene compound. In addition, a large red shift of around 100 nm is observed for the POSS compounds with respect to their precursors. These experimental results can only be accounted for by the spatial ordering induced by the POSS core that eases interactions, which otherwise would not occur. These results have been confirmed by time‐dependent density functional theory (TDDFT) calculations that exclude a photoinduced electron transfer (PET) process in the POSS compounds.     

Cyclotrimerization‐Induced Chiral Supramolecular Structures of 4‐Ethynyltriphenylamine on Au(111) Surface

Cyclotrimerization‐induced chiral supramolecular structures of 4‐ethynyltriphenylamine (ETPA) have been synthesized on the Au(111) surface through alkyne‐based reactions. Whereas the ETPA molecules adsorbed on the Au(111) surface remain inert and form a close‐packed self‐assembled structure at room temperature, the combination of scanning tunneling microscopy observations and theoretical calculations unambiguously reveal that the ETPA molecules cyclotrimerize to form new trimer‐like species—1,3,5‐tris[4‐(diphenylamino)phenyl]benzene (TPAPB)—after annealing at 323 K. Further annealing drives these cyclotrimerized TPAPB molecules to form chiral hexagonal supramolecular structures with an extraordinary self‐healing ability.     

Crystal Structures of the Carborane Dianions [1,4‐(PhCB10H10C)2C6H4]2− and [1,4‐(PhCB10H10C)2C6F4]2− and the Stabilizing Role of the para‐Phenylene Unit on 2 n+3 Skeletal Electron Clusters

While carboranes with 2 n+2 and 2 n+4 (n=number of skeletal atoms) skeletal electrons (SE) are widely known, little has been reported on carboranes with odd SE numbers. Electrochemical measurements on two‐cage assemblies, where two C‐phenyl‐ortho‐carboranyl groups are linked by a para‐phenylene or a para‐tetrafluorophenylene bridge, revealed two well separated and reversible two‐electron reduction waves indicating formation of stable dianions and tetraanions. The salts of the dianions were isolated by reduction with sodium metal and their unusual structures were determined by X‐ray crystallography. The diamagnetic dianions contain two 2 n+3 SE clusters where each cluster has a notably long carborane C–carborane C distance of ca 2.4 Å. The π conjugation within the phenylene bridge plays an important role in the stabilization of these carboranes with odd SE counts.     

Synthesis of Periphery‐Decorated and Core‐Initiated Borane Polyanionic Macromolecules

A new class of globular polybranched macromolecules that contain multiple anionic metallacarborane clusters at the o‐carborane periphery is reported. The water soluble high boron rich containing molecules could be of interest for boron neutron capture therapy (BNCT) as well as for drug delivery. The reinforced electrostatic noncovalent interactions between anionic polyethylene glycol cobaltabisdicarbollide (PEG‐COSAN) branches and the ammonium cation have been shown using ESI‐MS.     

Synthesis of Luminescent Covalent–Organic Polymers for Detecting Nitroaromatic Explosives and Small Organic Molecules

Three porous luminescent covalent‐‐organic polymers (COPs) have been synthesized through self‐polycondensation of the monomers of tris(4‐bromophenyl)amine, 1,3,5‐tris(4‐bromophenyl)benzene, and 2,4,6‐tris‐(4‐bromo‐phenyl)‐[1,3,5]triazine by using Ni‐catalyzed Yamamoto reaction. All the COP materials possess not only high Brunauer–Emmett–Teller (BET) specific surface area of about 2000 m² g⁻¹, high hydrothermal stability, but also graphene‐like layer texture. Interestingly, COP‐3 and COP‐4 show very fast responses and high sensitivity to the nitroaromatic explosives, and also high selectivity for tracing picric acid (PA) and 2,4,6‐trinitrotoluene (TNT) at low concentration (<1 ppm). In short, the COPs may be a new kind of material for detecting explosives and small organic molecules.     

Visible‐Light‐Promoted Photocatalytic B−C Coupling via a Boron‐Centered Carboranyl Radical: Facile Synthesis of B(3)‐Arylated o‐Carboranes

A visible‐light‐mediated in situ generation of a boron‐centered carboranyl radical (o‐C₂B₁₀H₁₁ ^. ) has been described. With eosin Y as a photoredox catalyst, 3‐diazonium‐o‐carborane tetrafluoroborate [3‐N₂‐o‐C₂B₁₀H₁₁][BF₄] was converted into the corresponding boron‐centered carboranyl radical intermediate, which can undergo efficient electrophilic substitution reaction with a wide range of (hetero)arenes. This general and simple procedure provides a metal‐free alternative for the synthesis of 3‐(hetero)arylated‐o‐carboranes.     

Nickel‐Catalyzed Cross‐Coupling Reactions of o‐Carboranyl with Aryl Iodides: Facile Synthesis of 1‐Aryl‐o‐Carboranes and 1,2‐Diaryl‐o‐Carboranes

A nickel‐catalyzed arylation at the carbon center of o‐carborane cages has been developed, thus leading to the preparation of a series of 1‐aryl‐o‐carboranes and 1,2‐diaryl‐o‐carboranes in high yields upon isolation. This method represents the first example of transition metal catalyzed C,C′‐diarylation by cross‐coupling reactions of o‐carboranyl with aryl iodides.     

Carborane Dyads for Photoinduced Electron Transfer: Photophysical Studies on Carbazole and Phenyl‐o‐carborane Molecular Assemblies

o‐Carborane‐based donor–acceptor dyads comprising an o‐carboranyl phenyl unit combined with N‐carbazole ( 1 ) or 4‐phenyl‐N‐carbazole ( 2 ) were prepared, and their dyad characters were confirmed by steady‐state photochemistry and photodynamic experiments as well as electrochemical studies. The absorption and electrochemical properties of the dyads were essentially the sum of those of the carbazole and o‐carboranyl phenyl units; this indicates negligible interaction between the carbazole and o‐carborane units in the ground state. However, the emission spectra of 1 and 2 indicated that carbazole fluorescence was effectively quenched and a new charge‐transfer (CT) emission was observed in solvents, varying from hexane to acetonitrile, which exhibited large Stoke shifts. The CT emission properties of o‐carborane‐based dyads were further analyzed by using Lippert–Mataga plots to show that unit charge separation occurred to form a charge‐separated species in the excited state, namely, 1?2 . This excited‐state species was confirmed by nanosecond transient absorption spectra and spectroelectrochemical measurements; the photoexcitation of carbazole generated the CT state in which a radical cation and anion were formed at the carbazole and o‐carborane units, respectively, within a few nanoseconds. DFT calculations corroborated the presence of this CT species and showed localized populations of the highest singly occupied molecular orbital on 2 in the reduced anionic state. As a result, molecular assemblies formed by linking the carbazole group with the o‐carborane cage through a phenylene or multi‐phenylene spacer revealed that the photoinduced electron‐transfer process occurred intramolecularly.     

Triazine dendrimers by divergent and convergent methods

Two types of dendrimers with a 1,3,5‐triazine ring at the branch point were synthesized by divergent and convergent methods. The divergent method began with 2,4,6‐tris(p‐nitroanilino)‐1,3,5‐triazine as a trifunctional core. Each cycle involved the reduction of the peripheral NO₂ group followed by a reaction with 2‐chloro‐4,6‐bis(p‐nitroanilino)‐1,3,5‐triazine. The synthetic cycle was completed by the coupling with 2,4‐dianilino‐6‐chloro‐1,3,5‐triazine (DACT) to eventually accomplish second‐generation dendrimers ([G2]₃‐C) bearing 12 benzene rings at their edge. The convergent approach started with the reaction of DACT with p‐nitrophenol to give rise to 2,4‐dianilino‐6‐(p‐nitrophenoxy)‐1,3,5‐triazine. The synthetic cycle consisted of reduction of the NO₂ group and coupling with 2,4‐dichloro‐6‐(p‐nitrophenoxy)‐1,3,5‐triazine. The final step was the connection of each monodendron with cyanuric chloride to produce tridendron; in this way, the second‐generation dendrimer ([EG2]₃‐C) was obtained. Gel permeation chromatography analyses indicated the aggregation of dendrimers in solution. Ultraviolet spectroscopic analyses revealed that the larger dendrimer had a more conjugated electron system from the core to the periphery. The thermal properties were evaluated by thermogravimetric analysis (TGA); excellent heat resistance was indicated, especially in [G1]₃‐C, which included alternately imine‐like nitrogen‐linked 1,3,5‐triazine and benzene rings. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4385–4395, 2000     

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.     

(Benzene‐1,3,5‐triyl)tris[phosphine] (C6H3(PH2)3) and (Benzene‐1,3,5‐triyl)tris[phosphonic Acid] (C6H3[P(O)(OH)2]3). Absence of Hydrogen Bonding in Solid Primary Phosphines

The prolonged photo‐Arbuzov reaction (3 weeks, Hg lamp) of 1,3,5‐trichloro‐benzene with a large excess of trimethyl phosphite (as a solvent) at 50° gives moderate yields of dimethyl (3,5‐dichlorophenyl)phosphonate ( 1 ; 14.5%), tetramethyl (5‐chloro‐1,3‐phenylene)bis[phosphonate] ( 2 ; 35.4%), and hexamethyl (benzene‐1,3,5‐triyl)tris[phosphonate] ( 3 ; 30.1%). The products can be separated by fractional distillation. Acid hydrolysis of the esters gives almost quantitative yields of the corresponding phosphonic acids 4 – 6 . Reduction of the esters 1 – 3 by LiAlH₄ in tetrahydrofuran affords the primary phosphines (3,5‐dichlorophenyl)phosphine ( 7 ; 46.5%), (5‐chloro‐1,3‐phenylene)bis[phosphine] ( 8 ; 34.5%) and (benzene‐1,3,5‐triyl)tris[phosphine] ( 9 ; 25.2% yield). In the crude reduction products from 2 (preparation of 8 ) and from 3 (preparation of 9 ), (3‐chlorophenyl)phosphine and (1,3‐phenylene)bis[phosphine], respectively, are observed as by‐products. All compounds are characterized by standard analytical, spectroscopic, and (for 1, 7 , and 8 ) structural techniques. The arrangement of the molecules in the crystal structures of 7 and 8 suggest that H‐bonding between the primary arylphosphines is virtually insignificant for the packing of the components. This is in marked contrast to the importance of H‐bonding for the supramolecular chemistry of arylamines. The new primary polyphosphines and polyphosphonic acids are to be employed in the construction of extended arrays.     

Structural Changes in 2‐Diarylthiophene‐Substituted Starburst Compounds upon Charging: A Theoretical and Spectroelectrochemical Study

The role of charging in structural changes of 2‐diarylaminothiophene‐substituted starburst compounds is clarified by combining theoretical and spectroelectrochemical studies. A systematic and comparative theoretical calculation based on density functional theory and semiempirical Austin Model 1 (AM1) calculations is performed on the neutral and charged states of four model tris(5‐diarylamino‐5‐thienyl)‐terminated starburst compounds with a central triphenylamine and 1,3,5‐triphenylbenzene moiety. Our results indicate that the charging of molecules leads to structural changes by quinoid‐type components mostly on the dendrimers terminated by phenothiazinyl fragments. Based on the optimal geometries, the spectroscopic properties were calculated using the semiempirical Zerner’s intermediate neglect overlap method. The presented theoretical results and the spin electron distributions of charged states and their spectra are supported by the spectroelectrochemical observations caused by the different electron localization within the studied molecules after charging. The satisfactory agreement between theoretical electronic transitions and experimental values indicates that a rational design of tunable molecular layers in organic devices based on the starburst compounds described is possible.     

碳十硼烷及其衍生物的反应性及应用

碳十硼烷(C₂B₁₀H₁₂)是由2个C原子和10个B原子组成的二十面体笼状结构大分子,有邻位、间位和对位三种异构体。碳十硼烷庞大的体积以及类芳香族三维刚性结构使它具有优异的高温稳定性和化学稳定性,良好的溶解性使其具有广泛而灵活的应用。本文总结了近年来碳十硼烷和碳十硼烷衍生物在C原子、B原子上的化学反应性以及在环加成和金属络合方面的研究。另外,由于碳十硼烷衍生物特殊的立体结构,优异的耐高温性、热氧化性及高硼含量,本文综述了碳十硼烷衍生物近年来在功能材料、催化剂及生物医药等多个领域的应用进展。     

General Access to Aminobenzyl‐o‐carboranes as a New Class of Carborane Derivatives: Entry to Enantiopure Carborane–Amine Combinations

The convenient synthesis of original aminobenzyl‐o‐carboranes, which represent a new class of nitrogenated carborane derivatives, is described. These novel compounds have been efficiently prepared starting from commercially available aromatic aldehydes and monosubstituted o‐carboranes via carboranyl alcohols and chlorides as intermediates. The key step of this methodology is a selective nucleophilic amination under mild conditions that allows the formation of the expected amines while limiting the partial deboronation of the carborane cluster. This general strategy has been applied to the preparation of a wide variety of aminobenzyl‐o‐carboranes. The extension of this pathway to the synthesis of enantiopure carborane–amine combinations is also described.     

Triggering Gel Formation and Luminescence through Donor–Acceptor Interactions in a C3‐Symmetric Tris(pyrene) System

Straightforward modulation of the gelation, absorption and luminescent properties of a tris(pyrene) organogelator containing a C₃‐symmetric benzene‐1,3,5‐tricarboxamide central unit functionalized by three 3,3′‐diamino‐2,2′‐bipyridine fragments is achieved through donor–acceptor interactions in the presence of tetracyanoquinodimethane.     

Facial Synthesis of o‐Carborane‐Substituted Alkenes and Allenes by a Regioselective Ene Reaction of 1,3‐Dehydro‐o‐carborane

1,3‐Dehydro‐o‐carborane is a useful synthon for selective cage boron functionalization of o‐carboranes. It reacts readily with alkenes or alkynes to give a variety of cage B(3)‐alkenyl/allenyl o‐carboranes by ene reactions in very high yields and excellent regioselectivity. This can be ascribed to the highly polarized cage C?B multiple bond, which lowers the activation barriers of the ene reaction.     

Thermal and X‐ray powder diffraction studies of aliphatic polyester dendrimers

The syntheses and thermal and X‐ray powder diffraction analyses of three sets of aliphatic polyester dendrimers based on 2,2‐bis(hydroxymethyl)propionic acid as a repeating unit and 2,2‐dimethyl‐1,3‐propanediol, 1,5‐pentanediol, and 1,1,1‐tris(hydroxymethyl)ethane as core molecules are reported. These dendritic polyesters were prepared in high yields with the divergent method. The thermal properties of these biodendrimers were evaluated with thermogravimetric analysis and differential scanning calorimetry. The thermal decomposition of the compounds occurred around 250 °C for the hydroxyl‐ended dendrimers and around 150 °C for the acetonide‐protected dendrimers. In addition, the crystallinity of the lower generation dendrimers was evaluated with X‐ray powder diffraction. The highest crystallinity and the highest melting points were observed for the first‐generation dendritic compounds. The higher generation dendrimers showed weaker melting transitions during the first heating scan. Only the glass‐transition temperatures were observed in subsequent heating scans. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5574–5586, 2004     

Aggregation‐Induced Electrochemiluminescence of Carboranyl Carbazoles in Aqueous Media

The aggregation‐induced electrochemiluminescence (AIECL) of carboranyl carbazoles in aqueous media was investigated for the first time. Quantum yields, morphologies, and particle sizes were observed to determine the electrochemiluminescence (ECL) performance of these aggregated organic dots (ODs). All compounds exhibit much higher ECL stability and intensity than the carborane‐free compound, demonstrating the essential role of the carboranyl motif. Moreover, the results of cyclic voltammetry (CV) suggest that oxidation/reduction reactions take place at the carboranyl motif. The excited states of ODs were proposed to be generated by the mechanism of surface state transitions. More importantly, these compounds show a reductive–oxidative mechanism in contrast to other organic materials that show oxidative–reductive mechanisms. Our experiments and data have established the relation between AIE organic structures and ECL properties that has a strong potential for biological and diagnostic applications.     

On the Electrochemistry and Spectroelectrochemistry of Small Model Star‐Shaped Compounds: 1,3,5‐Triaryl‐1‐Methoxybenzenes and 2,4,6‐Triaryl‐1,3,5‐Trimethoxybenzenes

Model structures of 1,3,5‐triarylbenzenes with a substituted benzene core linked to thienyl or 3,4‐ethylenedioxythienyl (EDOT) terminal groups are studied by electrochemical and in situ ESR/UV/Vis/NIR spectroelectrochemical techniques. Oxidative polymerization of the monomers results in C? C coupling of the thiophene moieties in the 5‐position, forming dimeric structures with bithiophene linkers as the first step. Both the doubly charged protonated dimer and the new dimer formed after proton release are studied in detail for 2,4,6‐tris[2‐(3,4‐ethylenedioxythienyl)]‐1‐methoxybenzene. Quite high stability of the doubly charged σ dimer formed on oxidation with unusual redox behavior at the electrode is observed. Density functional calculations of the molecular structure as well as spectroscopic and electronic properties of charged states in 1,3,5‐triarylbenzene derivatives in the monomeric, dimeric, and oligomeric form are presented. The complex spectroelectrochemical response of a thin solid film formed on the electrode surface upon potentiodynamic polymerization indicates the existence of different charge states of oligomeric structures within the solid matrix.