Carlos

Herein we show that replacing the two meso carbon atoms of the polycyclic aromatic hydrocarbon (PAH) bisanthene by boron atoms transforms a near-infrared dye into an efficient blue luminophore. This observation impressively illustrates the impact of boron doping on the frontier orbitals of PAHs. To take full advantage of this tool for the targeted design of organic electronic materials, the underlying structure–property relationships need to be further elucidated. We therefore developed a modular synthesis sequence based on a Peterson olefination, a stilbene-type photocyclization, and an Si–B exchange reaction to substantially broaden the palette of accessible polycyclic aromatic organoboranes and to permit a direct comparison with their PAH congeners.

Desirable deficiency: A modular synthesis approach provides access to extended polycyclic aromatic hydrocarbons containing electron-deficient boron atoms (see picture). The compounds obtained are air- and water-stable, bright blue luminophores and show reversible redox behavior.

Even though 2,2′-diiodo- and 2,2′-dibromobiaryls represent accomplished precursors for heterofluorenes and other extended π-conjugated systems, their preparation still remains nontrivial when structural diversity of the biaryl backbone is required. Herein, we report a convenient method for the preparation of various 2,2′-diiodobiaryls from 2-iodobiaryls via cyclic diaryliodonium intermediates. An iodinative ring-opening of the diaryliodonium salts, mediated by a copper/diamine catalyst system, is able to afford the corresponding 2,2′-diiodobiaryls under mild conditions. The versatility of this two-step approach is demonstrated by the preparation of hitherto unexplored tetraiodoteraryls and their conversion into ladder-type π-conjugated systems.

Biaryl iodination: 2-Iodobiaryls can be readily converted to 2,2′-diiodobiaryls through an initial oxidation to form cyclic diaryliodonium salts, followed by a copper/diamine-catalyzed iodinative ring-opening under mild conditions. The versatility of this two-step protocol is demonstrated by the preparation of hitherto unexplored tetraiodoteraryls and their conversion into ladder-type π-conjugated systems.

A perylene dye was introduced directly as a linker into a metal–organic framework (MOF) during synthesis. Depending on the dye concentration in the MOF synthesis mixture, different fluorescent materials were generated. The successful incorporation of the dye was proven by using ¹³C and ²⁷Al MAS NMR spectroscopy, by solution NMR spectroscopy after digestion of the MOF sample, and by synthesizing a reference dye without connecting groups, which could coordinate on the metal–oxo cluster inside the MOF. Fluorescence quenching effects of the MOF linker, 2-aminoterephthalate, were observed and overcome by postsynthetic modification with acetic anhydride. We show here for the first time that amino groups, which can be used as anchoring points for covalent attachment of other molecules, are responsible for fluorescence quenching. Thus, a very promising strategy to implement switchable fluorescence into MOFs is shown here.

Switch it on! A very promising strategy to implement fluorescence into MOFs has been discovered. A perylene dye was introduced directly as a linker into a metal–organic framework (MOF) during synthesis. Amino groups, which can be used as anchoring points for covalent attachment of other molecules, are responsible for the fluorescence quenching. However, the fluorescence can be switched-on by postsynthetic modification of these groups (see figure).

A promising alternative strategy for designing mesoporous metal–organic frameworks (MOFs) has been proposed, by modifying the symmetry rather than expanding the length of organic linkers. By means of this approach, a unique MOF material based on the target [Zn₈(ad)₄] (ad=adeninate) clusters and C₃-symmetric organic linkers can be obtained, with trigonal microporous (ca., 0.8 nm) and hexagonal mesoporous (ca., 3.0 nm) 1D channels. Moreover, the resulting 446-MOF shows distinct reactivity to transition and lanthanide metal ions. Significantly, the transmetalation of Co^II or Ni^II on the Zn^II centers in 446-MOF can enhance the sorption capacities of CO₂ and CH₄ (16–21 %), whereas the impregnation of Eu^III and Tb^III in the channels of 446-MOF will result in adjustable light-emitting behaviors.

Star cluster: A ligand symmetry modulation strategy was developed to design a mesoporous metal–organic framework with C₃ symmetry ligands and large octazinc(II) clusters, which shows dual reactivity to transition and lanthanide metals, resulting in enhanced functionalization of gas sorption and luminescence for the modified materials (see figure).

A series of π-extended distyryl-substituted boron dipyrromethene (BODIPY) derivatives with intense far-red/near-infrared (NIR) fluorescence was synthesized and characterized, with a view to enhance the dye’s performance for fluorescence labeling. An enhanced brightness was achieved by the introduction of two methyl substituents in the meso positions on the phenyl group of the BODIPY molecule; these substituents resulted in increased structural rigidity. Solid-state fluorescence was observed for one of the distyryl-substituted BODIPY derivatives. The introduction of a terminal bromo substituent allows for the subsequent immobilization of the BODIPY fluorophore on the surface of carbon nano-onions (CNOs), which leads to potential imaging agents for biological and biomedical applications. The far-red/NIR-fluorescent CNO nanoparticles were characterized by absorption, fluorescence, and Raman spectroscopies, as well as by thermogravimetric analysis, dynamic light scattering, high-resolution transmission electron microscopy, and confocal microscopy.

Know your onions: A series of bright fluorescent boron dipyrromethene (BODIPY) dyes was synthesized and characterized (see figure); single crystals of one fluorophore reveal solid-state fluorescence. Subsequently, the far-red/near-infrared-fluorescent BODIPY dye was attached to carbon nano-onions, to give a red fluorescent carbon nanomaterial.

A new anionic framework {[Me₂NH₂]_0.125[In_0.125(H₂L)_0.25]⋅xDMF}_n (1) with one-dimensional (1D) channels along the c axis of about 13.06×13.06 Ų, was solvothermally synthesized and well characterized. Post-synthetic cation exchange of 1 with Eu³⁺, Tb³⁺, Dy³⁺, Sm³⁺ afforded lanthanide(III)-loaded materials, Ln³⁺@1, with different luminescent behavior, indicating that compound 1 could be used as a potential luminescent probe toward different lanthanide(III) ions. Additionally, compound 1 exhibits selective adsorption ability toward cationic dyes. Moreover, the RhB@1 realized the probing of different organic solvent molecules by tuning the energy transfer efficiency between two different emissions, especially for sensing DMF. This work highlights the practical application of luminescent guest@MOFs as sensors, and it paves the way toward other one/multi-color luminescent host–guest systems by rational selection of MOF hosts and guest chromophores with suitable emissive colors and energy levels.

Rainbow runner: A new anionic framework {[Me₂NH₂]_0.125[In_0.125(H₂L)_0.25]⋅x DMF}_n (1) with 1D channels was solvothermally synthesized. Post-synthetic cation exchange with Ln³⁺ and various dyes gave lanthanide(III)/dye-loaded metal–organic framework (MOF) materials Ln³⁺@1 and Dye@1 (see figure). Compound 1 could be used as a potential luminescent probe toward different lanthanide(III) ions. Moreover, one complex could be used as a probe for different organic solvent molecules, especially DMF molecules.

Novel luminescence-functionalized metal–organic frameworks (MOFs) with superior electrogenerated chemiluminescence (ECL) properties were synthesized based on zinc ions as the central ions and tris(4,4′-dicarboxylicacid-2,2′-bipyridyl)ruthenium(II) dichloride ([Ru(dcbpy)₃]²⁺) as the ligands. For potential applications, the synthesized MOFs were used to fabricate a “signal-on” ECL immunosensor for the detection of N-terminal pro-B-type natriuretic peptide (NT-proBNP). As expected, enhanced ECL signals were obtained through a simple fabrication strategy because luminescence-functionalized MOFs not only effectively increased the loading of [Ru(dcbpy)₃]²⁺, but also served as a loading platform in the ECL immunosensor. Furthermore, the proposed ECL immunosensor had a wide linear range from 5 pg mL⁻¹ to 25 ng mL⁻¹ and a relatively low detection limit of 1.67 pg mL⁻¹ (signal/noise=3). The results indicated that luminescence-functionalized MOFs provided a novel amplification strategy in the construction of ECL immunosensors and might have great prospects for application in bioanalysis.

Trap the light fantastic: Luminescence-functionalized metal–organic frameworks (MOFs) were synthesized by using Zn²⁺ as the central ion and a Ru complex as the ligand. This provided a method to use a metallic complex instead of a small organic molecule as a ligand to prepare MOFs. Moreover, MOFs were applied to the construction of a sensitive electrogenerated chemiluminescence biosensor (see figure).

Two novel semiconducting polymers based on benzodithiophene and dithienophosphole oxide (DTP) units are designed and synthesized. A novel electron-deficient DTP moiety is developed. Surprisingly, the introduction of DTP units brings highly polarizable characteristics, which is beneficial for the photocurrent in solar cells. Thus, the donor–acceptor type of conjugated polymers based on this novel acceptor has superior charge transfer properties and highly efficient PL quenching efficiencies. As a result, polymer solar cells (PSCs) with high power conversion efficiencies of 6.10% and 7.08% are obtained from poly(3,5-didodecyl-4-phenylphospholo[3,2-b:4,5-b']dithiophene–4-oxide-alt-4,8-bis(5-decylthiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene) (PDTP–BDTT) and PDTP–4-oxide-alt-4,8-bis(5-decylselenophen-2-yl)benzo[1,2-b:4,5-b']dithiophene) (PDTP–BDTSe), respectively, when the photoactive layer is processed with the 1,8-octanedithiol (ODT) additive. The PDTP–BDTSe copolymer is now the best performing DTP-based material for PSCs. Using the polarizable unit strategy determined in this study for the molecular design of conjugated polymers is expected to greatly advance the development of organic electronic devices.

Two novel copolymers, PDTP–BDTT and PDTP–BDTSe, containing dithienophosphole oxide units bring superior charge transfer properties by highly polarizable characteristics, which is beneficial for good performance in polymer solar cells.

The molecular crystals of acridonyl-tetraphenylethene (AD-TPE) exhibit an intriguing turn-on and color-tuned luminescence in response to mechanical grinding and hydrostatic compression. On the basis of in-depth experimental and computational studies, it is hypothesized that the origin of the piezochromic behavior from the D-phase to the B-phase is the change of the intramolecular geometrical conformation, especially for the torsion angle between the TPE and AD moiety. The different molecular conformation in the two distinctive solid phases causes the substantial switching of the intra­molecular charge transfer (ICT) process, which can be directly correlated with the subsequent fluorescence from locally excited (LE) state and ICT state in both phases. The AD-TPE molecular system presents a very rare example of high-contrast reversible fluorescence tuning driven by a switching of the excited state in the solid state under the mechanical stimuli, and thus provides a novel mechanism of the piezochromic behavior.

Tuning the solid state luminescence of organic materials under mechanical stimuli is an attractive subject for both the fundamental research and practical application in the optical recording and sensing. Herein, a structurally well-defined molecule, acridonyl-tetraphenylethene is reported, whose molecular crystals exhibit an intriguing turn-on and color-tuned luminescence with high contrast in response to the mechanical stimuli such as grinding and hydrostatic pressure.

A method for the synthesis of phosphabenzenes under iron catalysis is described. Thus, the FeI₂-catalyzed [2+2+2] cycloaddition of diynes with phosphaalkynes in m-xylene gave a variety of phosphabenzenes in good to high yields (up to 87 % yield).

Ironing out any difficulties: Unlike complexes of other transition metals, an iron catalyst enabled the synthesis of phosphabenzenes from 1,6-diynes and phosphaalkynes (see scheme). A variety of phosphabenzene derivatives were formed in good to high yield by FeI₂-catalyzed [2+2+2] cycloaddition reactions of these substrates in m-xylene.

A new strategy is reported for multicolor fluorescence writing on thin solid films with mechanical forces. This concept is illustrated by the use of a green-fluorescent pentiptycene derivative 1, which forms variably colored fluorescent exciplexes: a change from yellow to red was observed with anilines, and fluorescence quenching (a change to black) occurred in the presence of benzoquinone. Mechanical forces, such as grinding and shearing, induced a crystalline-to-amorphous phase transition in both the pristine and guest-adsorbed solids that led to a change in the fluorescence color (mechanofluorochromism) and a memory of the resulting color. Fluorescence drawings of five or more colors were created on glass or paper and could be readily erased by exposure to air and dichloromethane fumes. The structural and mechanistic aspects of the observations are also discussed.

Memorable art: Multicolor fluorescence writing was possible on thin solid films of a pentiptycene–anthracene conjugated system (see picture). This technique relies on the formation of fluorescent exciplexes with aniline vapors and on force-induced fluorescence color memory. The drawings were erased by blowing air over the surface and by exposure to dichloromethane fumes.

The first syntheses of hybrid structures that lie between subphthalocyanines and subporphyrins are reported. The versatile single-step synthetic method uses a preformed aminoisoindolene to provide the bridging methine unit and its substituent while trialkoxyborates simultaneously act as Lewis acid, template, and provider of the apical substituent. The selection of each component therefore allows for the controlled formation of diverse, differentially functionalized systems. The new hybrids are isolated as robust, pure materials that display intense absorption and emission in the mid-visible region. The new compounds are further characterized in solution and solid state by variable-temperature NMR spectroscopy and X-ray crystallography, respectively.

The first syntheses of subphthalocyanine–subporphyrin hybrid structures are reported. The new hybrids are isolated as robust, pure materials that display intense absorption and emission in the mid-visible region, and are further characterized in solution and solid state by variable-temperature NMR spectroscopy and X-ray crystallography, respectively.