Carlos

A series of symmetric and asymmetric benzo[c,d]indole-containing aza boron dipyrromethene (aza-BODIPY) compounds was synthesized by a titanium tetrachloride-mediated Schiff-base formation reaction of commercially available benzo[c,d]indole-2(1H)-one and heteroaromatic amines. These aza-BODIPY analogues show different electronic structures from those of regular aza-BODIPYs, with hypsochromic shifts of the main absorption compared to their BODIPY counterparts. In addition to the intense fluorescence in solution, asymmetric compounds exhibited solid-state fluorescence due to significant contribution of the vibronic bands to both absorption and fluorescence as well as reduced fluorescence quenching in the aggregates. Finally, aggregation-induced emission enhancement, which is rare in BODIPY chromophores, was achieved by introducing a nonconjugated moiety into the core structure.

Old dyes with new tricks: A series of symmetric and asymmetric benzo[c,d]indole-containing aza-BODIPY dyes were synthesized. In addition to the hypsochromic shift of absorption and fluorescence compared to their BODIPY counterparts, solid-state fluorescence through asymmetrization and aggregation-induced emission enhancement through introduction of a nonconjugated moiety into the core structure were achieved (see figure).

This paper reports on the development of an efficient synthesis of enantiopure phospha[6]helicenes through a [2+2+2] alkyne cyclotrimerization reaction. The corresponding gold complexes proved to be highly efficient both in terms of catalytic activity and enantioselectivity in [2+2] and [4+2] cycloaddition reactions. Furthermore, in the presence of an external nucleophile, such as water or alcohols, the tandem cyclization/addition reactions take place in high yields and excellent diastereo- and enantioselectivities.

Enantiopure phospha[6]helicenes are easily synthesized through a [2+2+2] alkyne cyclotrimerization reaction. The corresponding gold complexes proved to be highly efficient both in terms of catalytic activity and enantioselectivity in [2+2], [4+2] cycloadditions and tandem cyclization/addition reactions.

Turn-on and color-tuned piezochromic luminescence of acridonyl-tetraphenylethene(AD-TPE) with high-contrast is obtained by B. Xu, W. Tian, and colleagues in response to external mechanical stimuli. The results on page 4005 indicate that the unique behavior is driven by a switching of the excited state in solid state from localized excited (LE) state to intramolecular charge transfer (ICT) state under mechanical stimuli, which will inspire a new approach to realize the piezochromic luminescent materials and give a new insight into the nature of the piezochromic behavior.

New clustomesogens (i.e., metal atom clusters containing liquid crystalline (LC) materials) have been obtained by grafting neutral cyanobiphenyl (CB)- or cholesteryl-containing tailor-made dendritic mesomorphic triphenylphosphine oxide ligands on luminescent (M₆Clⁱ₈)⁴⁺ octahedral cluster cores (M=Mo, W). The LC properties were studied by a combination of polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray powder diffraction analyses. While the organic ligands showed various mesophase types ranging from nematic, SmA columnar (SmA_Col), SmA, and SmC phases, it turned out that the corresponding clustomesogens formed layered phases (SmA) over a wide range of temperatures that depend on the nature and density of mesogenic groups employed. Intrinsic luminescence properties of the cluster precursors are preserved over the entire range of LC phase existence.

Clustomesogens are metal atom clusters containing liquid crystalline materials. They have been obtained by grafting neutral cyanobiphenyl- or cholesteryl-containing tailor-made dendritic mesomorphic triphenylphosphine oxide ligands on luminescent (M₆Clⁱ₈)⁴⁺ octahedral cluster cores (M=Mo, W).

The longitudinal extension of cycloparaphenylenes (CPP) towards ultrashort carbon nanotubes (CNTs) is essential for the solution based bottom-up synthesis of CNTs. Herein, the longitudinal extension of the CPP skeleton by the introduction of hexaphenylbenzene units towards polyarylated [n]CPPs is described. Further, the applicability of the Scholl reaction to selectively form graphenic sidewalls is demonstrated. The ring size and substitution patterns of the polyarylated [n]CPPs were varied to overcome strain-induced side reactions during the oxidative cyclodehydrogenation and cyclic para-hexa-peri-hexabenzocoronene trimers ([3]CHBCs) were selectively obtained. This concept is envisioned as an access to ultrashort carbon nanotubes subject to the condition that further benzene rings with the right connectivity will be inserted.

All that it′s cutout to be: Polyarylated [n]cycloparaphenylenes are intermediates on the way to ultra-short carbon nanotubes (CNT). Different polyarylated [n]CPPs can be prepared and their oxidative cyclodehydrogenation leads to CPPs that are cutouts from CNTs.

A facile and versatile approach was developed to access ambipolar boron-containing macrocycles. Two examples of new conjugated cyclic motifs are presented with carbazole moieties as donors and borane moieties as acceptors embedded into the ring system. They were first predicted using computational methods. Possible targets with appropriately shaped π-conjugated bridges that minimize the overall ring strain were identified and their geometry was optimized by DFT methods. The synthetic demonstration was then accomplished using organometallic condensation reactions under high dilution conditions. The resulting monodisperse macrocycles provide important insights into the design principles necessary for the preparation of new unstrained macrocycles with interesting optical and electronic characteristics. The current research also offers a more general approach to conjugated ambipolar B/N macrocycles as a promising new family of (opto)electronic materials.

Changing shapes: Guided by theoretical calculations, the conjugated fluorene bridges or the borane moieties in a strained tetramer are partially replaced with carbazoles, resulting in hybrid macrocycles with new shapes and sizes. These macrocycles are ambipolar and show interesting emission characteristics and anion response, including anion-triggered geometry changes.

A new highly efficient and versatile poly(benzyl ether) dendritic organogelator HPB-G₁ with 2-(2′-hydroxyphenyl)benzoxazole (HPB) at the focal point has been designed and synthesized. HPB-G₁ can form stable organogels toward various apolar and polar organic solvents. Further studies revealed that intermolecular multiple π–π stacking interactions are the main driving forces for the formation of the organogels. Notably, dendron HPB-G₁ exhibited a significantly enhanced emission in the gel state in contrast to weak emission in solution. Most interestingly, these dendritic organogels exhibited multiple stimuli-responsive behaviors upon exposure to environmental stimuli, including temperature, sonication, shear stress, and the presence of anions, metal cations, acids/bases, thus leading to reversible sol–gel phase transitions.

Smart fluorescence: A highly efficient and versatile dendron with 2-(2′-hydroxyphenyl)benzoxazole at the core that can form stable organogels with various apolar and polar organic solvents has been developed. These fluorescent dendritic organogels exhibit gelation-induced enhanced fluorescence emission and multiple stimuli-responsive behaviors (see figure).

Multicomponent surface architectures are introduced that operate with three different dynamic covalent bonds. Disulfide exchange under basic conditions accounts for the growth of π stacks on solid surfaces. Hydrazone exchange under acidic conditions is used to add a second coaxial string or stack, and boronic ester exchange under neutral conditions is used to co-align a third one. The newly introduced boronic ester exchange chemistry is compatible with stack and string exchange without interference from the orthogonal hydrazone and disulfide exchange. The functional relevance of surface architectures with three different dynamic covalent bonds is exemplified with the detection of polyphenol natural products, such as epigallocatechin gallate, in competition experiments with alizarin red. These results describe synthetic strategies to create functional systems of unprecedented sophistication with regard to dynamic covalent chemistry.

Designer architectures: Disulfide exchange under basic conditions, hydrazone exchange under acidic conditions, and boronic ester exchange at neutral pH values are combined to build multicomponent functional surface architectures using dynamic covalent chemistry. TSA/TSR=templated stack addition/release.

A rational synthetic procedure for the preparation of a series of pyrene-based neutral and dicationic bis-azole compounds is reported. The method allows the tailored design of pyrene-based azoles with different substituents at the nitrogen atoms of the heterocycles, for which the relative conformation of the resulting bis-azoles can be easily controlled. The bis-azoliums were used for the preparation of the related diplatinum complexes by reaction with [{Pt(ppy)(μ-Cl)₂}₂] (ppy=2-phenylpyridinate). The X-ray molecular structure of one of the resulting compounds, a diplatinum(II) bis(N-heterocyclic carbene) complex, is described. Studies on the photophysical properties of all new species are described. The emission of the bis-azole-based compounds seems to be independent of their substitution patterns, which basically indicates that physical properties such as solubility, melting point, and viscosity can be fine-tuned while maintaining the luminescence properties. Finally, the energies associated with the HOMO and LUMO levels suggest that this family provides versatility to match the energy levels of a wide range of host materials, which is important for the preparation of organic light-emitting devices.

Tailored azoles: A series of pyrene-based neutral and dicationic bis-azolium compounds with different substitution patterns was obtained. The bis-azolium compounds were used for the preparation of Pt^II complexes bearing the 2-phenylpyridinate ligand. The photophysical properties of all of the resulting compounds were evaluated; they show a wide range of HOMO and LUMO levels (see figure) suitable for matching with various host materials.

A route is reported for the synthesis of two electron-accepting phthalocyanines featuring linkers with different lengths as sensitizers for p-type dye-sensitized solar cells (DSSCs). Importantly, our devices based on novel nanorod-like CuO photocathodes showed high efficiencies of up to 0.191 %: the highest value reported to date for CuO-based DSSCs.

The longer the better: Novel electron-accepting zinc phthalocyanines with different linker lengths performed well in combination with nanorod-like CuO electrodes in p-type dye-sensitized solar cells. A particularly high efficiency of 0.191 % was observed with a photosensitizer containing a carboxyethynyl anchor (see picture; R is a branched alkyl group).