Base-promoted decarboxylative azo couplings of carboranyl carboxylic acids with diazo salts have been developed to provide trans-azocarboranes in high yields (up to 94%). This approach is simple, efficient, and compatible with various functional groups. Mechanistically, the coupling has been proven to proceed in a nonradical pathway, which is distinct from those classical decarboxylative couplings.

The structure–property relationship of carborane-embedded cationic iridium(III) complexes was investigated in this work, especially with donor–acceptor-type ligands. Firstly, an efficient synthetic approach for the new donor–acceptor-type ligands (2 and 4) was developed. By using these ligands, novel iridium(III) complexes II and IV were prepared. Complex IV shows about a 92 nm red-shift in solution (ΦP = 0.13 in ethanol), and the emission color has an obvious change from green to red when compared with the Model complex. In addition, the photophysical characteristics of complex IV are quite sensitive to the oxygen level in living cells, based on which endocellular hypoxia imaging of complex IV has been realized by the phosphorescence lifetime imaging microscopy (PLIM) technology. Besides the experimental studies, density functional theory (DFT) and time dependent DFT (TD-DFT) calculations have been successfully applied to investigate the excited-state electronic structures of carborane-modified iridium complexes.

A novel series of heteroleptic iridium complexes with 2-phenyl-pyridine as a main ligand and carborane-functionalized 2,2′-bipyridine as an ancillary ligand were synthesized, and characterized as [Ir(ppy)2(By)]PF6 (where ppy is 2-phenyl-pyridine, By is 5-(2-R-Cb)-2,2′-bipyridine, R = H (2a), CH3 (2b), Ph (2c), iPr (2d) and iBu (2e), or By is 4-(2-R-Cb)-2,2′-bipyridine while R = H (3a), CH3 (3b), Ph (3c), iPr (3d) and iBu (3e), Cb = o-carboran-1-yl). The R groups and the substitution sites of carborane on the pyridine ring have caused differences in the emission properties of these complexes. In addition, the quantum efficiency of [Ir(ppy)2(By)]PF6 complexes has been tuned as well through the introduction of various 2-R-substituted o-carboranes into the ancillary ligand 2,2′-bipyridine, no matter in the solid state (from 0.12 to 0.25) or in solution (from 0.04 to 0.25). The emission color was tuned from yellow to red by the o-carboranyl unit because of its inductive effect. Density functional theory (DFT) and time dependent DFT (TD-DFT) calculations have been applied to investigate excited-state electronic structures of the newly synthesized complexes, which are consistent with the observed red-shift emissions.

Mitochondria as vital intracellular organelles play critical roles in multiple physiological processes, and their polarity is a crucial characteristic that can reveal the intracellular environment and impact cellular events. In this work, we designed and synthesized a novel series of highly emissive and environmentally sensitive phosphorescent iridium(III) complexes (2a–2e, 3a–3e and 4) functionalized by o-carborane. These complexes showed high emission quantum yields both in solution and in solid state (up to ΦPL = 0.82), long emission lifetime and tunable emission wavelength over 74 nm by introduction of a carboranyl motif in their ligands. Importantly, all the complexes have shown significant solvatochromic effects in contrast to the carborane-free control complex. Among them, complex 2d shows the highest sensitivity to polarity of solvents with a MPPS (maximum peak phosphorescence shift) value of 42 nm and clear dependence of phosphorescence lifetime on solvent polarity. Interestingly, complex 2d can easily penetrate into cells and preferentially distribute in mitochondria. To utilize these properties, the first phosphorescent imaging of mitochondrial polarity has been realized by photoluminescence lifetime imaging microscopy (PLIM), which can monitor mitochondria-relevant cellular processes such as cell apoptosis and distinguish cancer cells from normal cells. Compared to intensity-based sensing, lifetime-based detection is independent of the probe concentration, excitation power and photobleaching of probes, which can show high accuracy and reproducibility.

AbstractThe development of organic single-molecule solid-state white emitters holds a great promise for advanced lighting and display applications. Highly emissive single-molecule white emitters were achieved by the design and synthesis of a series of o-carborane-based luminophores. These luminophores are able to induce multiple emissions to directly emit high-purity white light in solid state. By tuning both molecular and aggregate structures, a significantly improved white-light efficiency has been realized (absolute quantum yield 67 %), which is the highest value among the known organic single-molecule white emitters in the solid state. The fine-tuning of the packing modes from H- to J- and cross-stacking aggregates as well as intermolecular hydrogen bonds are successful in one molecular skeleton. These are crucial for highly emissive white-light emission in the solid state.

An iridium-catalyzed cage B–H sulfonamidation of o-carborane directed by a carboxylic acid group is reported that proceeds in the absence of ligands or external oxidants. A series of sulfonyl azides can be selectively sulfonamidated at the B(4) site in high yields with excellent functional group tolerance. This approach can also be applied to aryl and aliphatic azides. Innocuous CO2 and N2 were released as byproducts. In addition, the carboxylic acid group can be easily removed under mild conditions.

The Heck reaction between arenes and allyl acetate has led to cinnamyl derivatives and allyl products depending on the regioselectivity of β-elimination. The regioselectivity can be controlled by the solvent in the Rh(III)-catalyzed arene–allyl acetate coupling via C–H activation: (1) in THF, cinnamyl derivatives via β-H elimination were generated; (2) in MeOH, allyl products via β-OAc elimination were produced. Both routes have advantages such as excellent γ-selectivity toward allyl acetate, good to excellent yields, and broad substrate scope.

An effective photoredox-mediated tandem phosphorylation/cyclization reaction of diphenylphosphine oxide with three types of radical acceptors leads to P(O)Ph2-containing phenanthridines, isoquinolines, and indolin-2-ones by formation of both C–P and C–C bonds. [Ir(ppy)2(dtbpy)]PF6 (1 mol %) was used as the catalyst, CsF or Cs2CO3 as the base, and K2S2O8 as the oxidant. A series of functional groups can be tolerated at room temperature. Moderate to good yields were generated.

The reactions of the 16e half-sandwich complex CpCoS2C2B10H10 (1), diazo esters, and various 1,6-diynes (3a–i; PhN(CH2C≡CH)2, 4-Me-PhN(CH2C≡CH)2, 4-OMe-PhN(CH2C≡CH)2, 4-F-PhN(CH2C≡CH)2, BzN(CH2C≡CH)2, O(CH2C≡CH)2, C(Ac)2(CH2C≡CH)2, N(CH2C≡CH)3, NH(CH2C≡CH)N(CH2C≡CH)2) were investigated, in which two novel types of B–H activated products CpCoS2B10H9(CH2CO2Et)C5H3N(R)(CH═CHCO2Et) (4a–c; R = Ph, 4-Me-Ph, 4-OMe-Ph) and the key intermediate CpCoS2B10H9(CHCO2Me) (CH2CO2Me) (9) were isolated. 9 features a reactive Co–B bond, which triggers insertion of various 1,6-diynes to further lead to different final products. Substrates 3a–c are activated by the Co–B bond to produce o-carborane derivatives 4a–c which are functionalized by a cobalt-complexed η3-pyrrolylmethyl group. The pyrrole ring is formed by in situ ring closure of 1,6-diynes. Control experiments and isolation of the intermediate CpCoS2B10H9(CHCO2Me)(CH2CO2Me)HC═CCH2N(4-Me-Ph)(CH2C≡CH) (10) support the proposed mechanism concerning the formation of 4a–c analogues by oxidation. All of the new complexes were characterized by NMR, IR, elemental analysis, and mass spectrometry. The structures of 4a–6a and 9 were determined by single-crystal X-ray diffraction analysis as well.

Three coordination polymers {[Co2(AQTC)(H2O)6]·6H2O}n (1), {[M2(AQTC)(bpym)(H2O)6]·6H2O}n (M = Co(2), Ni(3)) have been synthesized and structurally characterized, where H4AQTC is anthraquinone-1,4,5,8-tetracarboxylic acid and bpym is 2,2′-bipyrimidine. Complex 1 features a 3-D structure, where layers of Co2(AQTC) are cross-linked by Co–H2O chains. Complexes 2 and 3 are isostructural and display 1-D chain structures. The chains are connected through hydrogen-bonding interactions to form 3-D supramolecular structures. Magnetic properties of these complexes are investigated. Compound 1 shows canted antiferromagnetism and slow relaxation below 4.0 K. For complexes 2 and 3, dominant antiferromagnetic interactions are observed. The luminescent properties of the three complexes are investigated as well.

A series of isostructural two-dimensional lanthanide complexes with the formula [Ln(Haqtc)(H2O)4·xH2O]n (Ln = Nd, 1; Sm, 2; Eu, 3; Tb, 4; Dy, 5; Er, 6.) were synthesized by treating H4aqtc (H4aqtc = anthraquinone-1,4,5,8-tetracarboxylic acid) with lanthanide(III) salts under hydrothermal conditions. 3-D structures are formed by inter-layer hydrogen bonds. Magnetic susceptibility measurements of complexes 4 and 5 in temperature range 2–300 K were performed, which showed dominant weak ferromagnetic interactions in 4 and slow magnetization relaxation in 5.Six isostructural lanthanide complexes, based on anthraquinone-1,4,5,8-tetracarboxylic acid (H4aqtc), showed layer-like structures and 3-D frameworks formed by interlayer hydrogen bonds. The magnetic properties of complexes 4 and 5 were investigated.Highlights► Six isostructural lanthanide complexes were synthesized and characterized. ► 3-D structures are formed by inter-layer hydrogen bonds. ► Magnetic properties results showed slow magnetization relaxation in complex 5.

A unique tubular molecular-assembly, constructed by β-cyclodextrin and Na[Ni(mnt)2], was identified by X-ray crystallography. Inclusion complex Na[Ni(mnt)2]@β-cyclodextrin (1) crystallized in space groupP21212 as hydrated head-to-head, tail-to-tail, and head-to-tail host pipelines with negatively charged [Ni(mnt)2]− guests included, exhibiting a 3:1 (host:guest) stoichiometry. The hydrophilic transition-metal coordination compound (Na[Ni(mnt)2]) was embedded within a hydrophobic cyclodextrin cavity, which resulted in a β-cyclodextrin trimer motif and one-third “empty” host packing model in the crystal. Induced circular dichroism (ICD) spectra of inclusion complex 1 was investigated, which indicated the same penetration pattern of the guests in host cavities in solution phase as that discovered in the crystal structure. In addition, PM3 quantum chemistry calculations strongly supported the co-conformational alignments of inclusion complex 1 that was identified in the crystal as well as in the solution.

A series of inclusion complexes between cyclodextrins (α-, β-, γ-cyclodextrin and HP-β-cyclodextrin, HP-β-cyclodextrin = 2-hydroxypropyl-β-cyclodextrin) and sodium maleonitriledithiolate (Na2mnt) were investigated by electronic spectra, induced circular dichroism (ICD) spectra, and quantum chemical studies. The inclusion complexes Na2mnt@α-cyclodextrin and Na2mnt@γ-cyclodextrin did not show any ICD signals, whereas Na2mnt@HP-β-cyclodextrin displayed two signs of splitting Cotton effects (CEs), with one positive CE couplet at 376 nm in the 365−410 nm region and the other negative at 277 nm in the 265−306 nm region. In addition, a dimeric host inclusion pattern of Na2mnt@HP-β-cyclodextrin in solution was determined by the method of continuous variation. Density functional theory (DFT) was used to assist assignment of the ICD signals in inclusion complexes Na2mnt@β-cyclodextrin and Na2mnt@HP-β-cyclodextrin in combination with the well-known Harata’s rule. The orientation of p → π* transition in Na2mnt chromophore was predicted by TD-DFT (time-dependent DFT) calculations to be along the C═C double bond instead of being perpendicular. Upon titrations with Zn2+ solutions, reversals of the p → π* transition-relevant ICD peak and splitting CE were experimentally observed in the cases of Na2mnt@β-cyclodextrin and Na2mnt@HP-β-cyclodextrin, respectively, which strongly supported our hypotheses on their coconformations and the subsequent conformational changes of mnt chromophores occurring during the titration procedures. Therefore, on the basis of both the experimental data and TD-DFT calculations, the HP-β-cyclodextrin dimer host in inclusion complex Na2mnt@HP-β-cyclodextrin was disclosed, which in turn generated the exciton coupling between the two individually included guests and produced the splitting CEs as well as the reversals of CEs.

A new inclusion complex of β-cyclodextrin with sodium maleonitriledithiolate (Na2mnt) was investigated by electronic spectra, induced circular dichroism (ICD), and quantum mechanics (QM) methods. The orientation of the guest anion inside the host cavity was studied by ICD spectra and analyzed by structural optimization using PM3 quantum chemical method. Finally, the inclusion constant was determined by both a linear and a non-linear fitting methods, which were based on the variation of ICD signals of the guest upon inclusion complexation with the host. The inclusion constant of Na2mnt/β-cyclodextrin was estimated to be (2.45 ± 0.15) × 103 or (3.10 ± 0.11) × 103 M−1 in solution by these two fitting methods.

A novel series of heteroleptic iridium complexes with 2-phenyl-pyridine as a main ligand and carborane-functionalized 2,2′-bipyridine as an ancillary ligand were synthesized, and characterized as [Ir(ppy)2(By)]PF6 (where ppy is 2-phenyl-pyridine, By is 5-(2-R-Cb)-2,2′-bipyridine, R = H (2a), CH3 (2b), Ph (2c), iPr (2d) and iBu (2e), or By is 4-(2-R-Cb)-2,2′-bipyridine while R = H (3a), CH3 (3b), Ph (3c), iPr (3d) and iBu (3e), Cb = o-carboran-1-yl). The R groups and the substitution sites of carborane on the pyridine ring have caused differences in the emission properties of these complexes. In addition, the quantum efficiency of [Ir(ppy)2(By)]PF6 complexes has been tuned as well through the introduction of various 2-R-substituted o-carboranes into the ancillary ligand 2,2′-bipyridine, no matter in the solid state (from 0.12 to 0.25) or in solution (from 0.04 to 0.25). The emission color was tuned from yellow to red by the o-carboranyl unit because of its inductive effect. Density functional theory (DFT) and time dependent DFT (TD-DFT) calculations have been applied to investigate excited-state electronic structures of the newly synthesized complexes, which are consistent with the observed red-shift emissions.

Three coordination polymers {[Co2(AQTC)(H2O)6]·6H2O}n (1), {[M2(AQTC)(bpym)(H2O)6]·6H2O}n (M = Co(2), Ni(3)) have been synthesized and structurally characterized, where H4AQTC is anthraquinone-1,4,5,8-tetracarboxylic acid and bpym is 2,2′-bipyrimidine. Complex 1 features a 3-D structure, where layers of Co2(AQTC) are cross-linked by Co–H2O chains. Complexes 2 and 3 are isostructural and display 1-D chain structures. The chains are connected through hydrogen-bonding interactions to form 3-D supramolecular structures. Magnetic properties of these complexes are investigated. Compound 1 shows canted antiferromagnetism and slow relaxation below 4.0 K. For complexes 2 and 3, dominant antiferromagnetic interactions are observed. The luminescent properties of the three complexes are investigated as well.

A unique tubular molecular-assembly, constructed by β-cyclodextrin and Na[Ni(mnt)2], was identified by X-ray crystallography. Inclusion complex Na[Ni(mnt)2]@β-cyclodextrin (1) crystallized in space groupP21212 as hydrated head-to-head, tail-to-tail, and head-to-tail host pipelines with negatively charged [Ni(mnt)2]− guests included, exhibiting a 3:1 (host:guest) stoichiometry. The hydrophilic transition-metal coordination compound (Na[Ni(mnt)2]) was embedded within a hydrophobic cyclodextrin cavity, which resulted in a β-cyclodextrin trimer motif and one-third “empty” host packing model in the crystal. Induced circular dichroism (ICD) spectra of inclusion complex 1 was investigated, which indicated the same penetration pattern of the guests in host cavities in solution phase as that discovered in the crystal structure. In addition, PM3 quantum chemistry calculations strongly supported the co-conformational alignments of inclusion complex 1 that was identified in the crystal as well as in the solution.