Diverse Synthesis of Novel Bisterpyridines via Suzuki-Type Cross-Coupling

Asymmetrically bridged aroyl-S,N-ketene acetal-based multichromophores with aggregation-induced tunable emission

Asymmetrically bridged aroyl-S,N-ketene acetals and aroyl-S,N-ketene acetal multichromophores can be readily synthesized in consecutive three-, four-, or five-component syntheses in good to excellent yields by several successive Suzuki-couplings of aroyl-S,N-ketene acetals and bis(boronic)acid esters. Different aroyl-S,N-ketene acetals as well as linker molecules yield a library of 23 multichromophores with substitution and linker pattern-tunable emission properties. This allows control of different communication pathways between the chromophores and of aggregation-induced emission (AIE) and energy transfer (ET) properties, providing elaborate aggregation-based fluorescence switches.

A library of 23 asymmetrically linked aroyl-S,N-ketene acetal solid-state emissive multichromophores accessed by one-pot multicomponent reactions exhibits AIE- and AIEE-active behavior as well as dual emission and potential energy transfer.

Neptunium(V) Isothiocyanate Complexes with 4'-Aryl-Substituted 2,2':6',2″-Terpyridines and N,N-Dimethylacetamide as Molecular Ligands

New complexes of neptunyl(V) isothiocyanate with 4'-aryl-substituted 2,2':6',2″-terpyridines (Terpy) and N,N-dimethylacetamide (DMA) were obtained: [(NpO₂)(4'-Ph-Terpy)(DMA)(NCS)]·DMA, [(NpO₂)(4'-(4-(CF₃)C₆H₄)-Terpy)(DMA)(NCS)]·2H₂O·DMA, [(NpO₂)(4'-(3-BrC₆H₄)-Terpy)(DMA)(NCS)]·DMA, and [(NpO₂)(4'-(2-(COOH)C₆H₄)-Terpy)(DMA)(NCS)]·DMA. The structures of the compounds were determined with X-ray diffraction analysis. The neptunium coordination polyhedra were found to be pentagonal bipyramids with O atoms of the NpO₂ groups in the apical positions and the equatorial planes formed by three N atoms of the terpyridine ligand, a N atom of the isothiocyanate anion, and an O atom of DMA. The influence of the substituents of the Ar group on the crystal structure is discussed. The IR spectra contain well-resolved bands of characteristic vibrations of all groups in the complex. The electronic absorption spectra are typical for neptunium(V) complexes and contain an intense narrow absorption band belonging to an f-f transition with a maximum of 988 nm and several long-wave satellites of lower intensity. The substituted terpyridines were shown to be efficient for the extraction of various valence forms of neptunium from the isothiocyanate solutions.

Probing Peripheral H-Bonding Functionalities in BN-Doped Polycyclic Aromatic Hydrocarbons

The replacement of carbon atoms at the zigzag periphery of a benzo[fg]tetracenyl derivative with an NBN atomic triad allows the formation of heteroatom-doped polycyclic aromatic hydrocarbon (PAH) isosteres, which expose BN mimics of the amidic NH functions. Their ability to form H-bonded complexes has never been touched so far. Herein, we report the first solution recognition studies of peripherally NBN-doped PAHs to form H-bonded DD·AA- and ADDA·DAAD-type complexes with suitable complementary H-bonding acceptor partners. The first determination of K_a in solution showed that the 1:1 association strength is around 27 ± 1 M^-1 for the DD·AA complexes in C₆D₆, whereas it rises to 1820 ± 130 M^-1 for the ADDA·DAAD array in CDCl₃. Given the interest of BN-doped polyaromatic hydrocarbons in supramolecular and materials chemistry, it is expected that these findings will open new possibilities to design novel materials, where the H-bonding properties of peripheral NH hydrogens could serve as anchors to tailor the organizational properties of PAHs.

Proton-Activated Amorphous Room-Temperature Phosphorescence for Humidity Sensing and High-Level Data Encryption

Supramolecular co-assembling terpyridine-derivatives with nanoclay (LP) are exploited to acquire efficient amorphous room-temperature phosphorescence (RTP). Experimental and theoretical investigations reveal that this co-assembly not only brings about a configuration transformation from the trans-trans (a) to the cis-trans (a'') form via the protonating process, significantly narrowing the singlet-triplet energy gap, thereby effectively facilitating the single-triplet ISC processes, but also well protects the triplet state and suppresses the nonradiative transitions via restricting molecular rotation and vibration by the hydrogen-bond interactions between them. Additionally, the flexible and transparent films, through co-assembling 1@LP (or 2@LP) with polyvinyl alcohol (PVA), also display excellent phosphorescence performance. Owing to their distinctive RTP performances, the RH sensing and high-level data encryption are achieved.

Optical Supramolecular Sensing of Creatinine

Calix[4]pyrrole phosphonate-cavitands were used as receptors for the design of supramolecular sensors for creatinine and its lipophilic derivative hexylcreatinine. The sensing principle is based on indicator displacement assays of an inherently fluorescent guest dye or a black-hole quencher from the receptor's cavity by means of competition with the creatinine analytes. The systems were thermodynamically and kinetically characterized regarding their 1:1 binding properties by means of nuclear magnetic resonance spectroscopy (¹H and ³¹P NMR), isothermal titration calorimetry, and optical spectroscopies (UV/vis absorption and fluorescence). For the use of the black-hole indicator dye, the calix[4]pyrrole was modified with a dansyl chromophore as a signaling unit that engages in Förster resonance energy transfer with the indicator dye. The 1:1 binding constants of the indicator dyes are in the range of 10⁷ M^-1, while hexylcreatinine showed values around (2-4) × 10⁵ M^-1. The competitive displacement of the indicators by hexylcreatinine produced supramolecular fluorescence turn-on sensors that work at micromolar analyte concentrations that are compatible with those observed for healthy as well as sick patients. The limit of detection for one of the systems reached submicromolar ranges (110 nM).

Synthesis, Structures, and Assembly of Geodesic Phenine Frameworks with Isoreticular Networks of [ n]Cyclo- para-phenylenes

A series of macrocycles were designed by rendering geodesic phenine frameworks in isoreticular networks of [ n]cyclo- para-phenylenes. Large, nanometer-sized molecules exceeding molecular weights of 2000 Da were synthesized by five-step transformations including macrocyclization of [6]cyclo- meta-phenylene panels. The dependence of both the molecular structures and the fundamental properties on the panel numbers was delineated by a combination of spectroscopic and crystallographic analyses with the aid of theoretical calculations. Interestingly, flexibility of the molecules via panel rotations depends on the hoop size, which has not been disclosed with the small isoreticular [ n]cylco- para-phenylenes. One of the macrocycles served as a host for C₇₀, and its association behaviors and crystal structures were revealed.

Finite phenine nanotubes with periodic vacancy defects

Discrete graphitic carbon compounds serve as tunable models for the properties of extended macromolecular structures such as nanotubes. Here, we report synthesis and characterization of a cylindrical C₃₀₄H₂₆₄ molecule composed of 40 benzene (phenine) units mutually bonded at the 1, 3, and 5 positions. The concise nine-step synthesis featuring successive borylations and couplings proceeded with an average yield for each benzene-benzene bond formation of 91%. The molecular structure of the nanometer-sized cylinder with periodic vacancy defects was confirmed spectroscopically and crystallographically. The nanoporous nature of the compound further enabled inclusion of multiple fullerene guests. Computations suggest that fusing many such cylinders could produce carbon nanotubes with electronic properties modulated by the periodic vacancy defects.

The Suzuki-Miyaura reaction as a tool for modification of phenoxyl-nitroxyl radicals of the 4H-imidazole N-oxide series

2-(3,5-Di-tert-butyl-4-hydroxyphenyl)-5-(4-iodophenyl)-4,4-dimethyl-4H-imidazole 3-oxide reacts with phenylboronic acid and its substituted derivatives in a cross-coupling reaction of the Suzuki-Miyaura type to form 5-biphenyl derivatives of 4H-imidazole-N-oxide. Interaction of the same compound with B2(pin)2 in the presence of PdCl2(PPh3)2 proceeds through the formation of intermediate 1,3,2-dioxoborolane and leads to the product of homocoupling: biphenyl-bis(imidazole). Oxidation of the resultant imidazoles with lead dioxide quantitatively yields stable conjugated phenoxyl-nitroxyl mono- and diradicals, which are of interest as electroactive paramagnetic materials. The crystal structure of the monoradical, 2,6-di-tert-butyl-4-[1-oxido-4-(biphenyl-4-yl)-5,5-dimethyl-1H-imidazole-2(5H)-ylidene]cyclohex-2,5-dienone, its magnetic susceptibility, EPR spectra of the obtained hybrid radicals in solution, and cyclic voltammetry characteristics of 4H-imidazoles were studied.

A chemically-responsive bis-acridinium receptor

The recognition and the chemical-response properties of a bis-acridinium triphenylene receptor were investigated.

Modulation of a coordination structure in a europium(iii)-based metallo-supramolecular polymer for high proton conduction

Developing high proton conducting solid materials is significant in the field of fuel cells. A europium(iii)-based metallo-supramolecular polymer with uncoordinated carboxylic acids (PolyEu-H) was successfully synthesized by modifying the synthesis conditions. The proton conductivity was enhanced with increasing the relative humidity (RH) from 30 to 95% RH. PolyEu-H showed about 10⁴ times higher proton conductivity than the polymer with coordinated carboxylic acids (PolyEu) and about 400 times higher than the polymer without carboxylic acids (PolyEu-2). The proton conductivity of PolyEu-H reached 4.45 × 10⁻² S cm⁻¹ at 95% RH and 25 °C and 5.6 × 10⁻² S cm⁻¹ at 75 °C. The activation energy, E_a was ultralow (0.04 eV), which indicates proton conduction based on the Grotthuss mechanism. The results indicate that efficient proton conduction occurs through proton channels formed by moisture in PolyEu-H.

Developing high proton conducting solid materials is significant in the field of fuel cells. We firstly synthesized europium(iii)-based metallo-supramolecular polymer with uncoordinated carboxylic acids (PolyEu-H), for high proton conduction.

Synthesis and photophysical properties of multi-Ru2+ terpyridine complexes: from di-nuclear linear to star-shaped hexa-nuclear architectures

Polyterpyridinyl multi-nuclear Ru²⁺ complex was synthesized through a heterocomplexation method. Introducing the tailed aliphatic chain greatly enhanced the solubility of multi-ionic paired complexes, which illustrated the photophysical and electrochemical structural differentiations.

Coupled molecular switching processes in ordered mono- and multilayers of stimulus-responsive rotaxanes on gold surfaces

Interfaces provide the structural basis for function as, for example, encountered in nature in the membrane-embedded photosystem or in technology in solar cells. Synthetic functional multilayers of molecules cooperating in a coupled manner can be fabricated on surfaces through layer-by-layer self-assembly. Ordered arrays of stimulus-responsive rotaxanes undergoing well-controlled axle shuttling are excellent candidates for coupled mechanical motion. Such stimulus-responsive surfaces may help integrate synthetic molecular machines in larger systems exhibiting even macroscopic effects or generating mechanical work from chemical energy through cooperative action. The present work demonstrates the successful deposition of ordered mono- and multilayers of chemically switchable rotaxanes on gold surfaces. Rotaxane mono- and multilayers are shown to reversibly switch in a coupled manner between two ordered states as revealed by linear dichroism effects in angle-resolved NEXAFS spectra. Such a concerted switching process is observed only when the surfaces are well packed, while less densely packed surfaces lacking lateral order do not exhibit such effects.

A highly selective, Hg2+ triggered hydrogelation: modulation of morphology by chemical stimuli

The morphology of a supramolecular hydrogel based on 4′-[4-(4-aminophenyl)phenyl]-2,2′:6′,2′′-terpyridine, exclusively with Hg²⁺, can be tuned by external chemical stimuli.

Synthesis and photophysical properties of some 6,6″-functionalized terpyridine derivatives

The synthesis and photophysical properties of several 6,6″ symmetrically substituted 4′-aryl-2,2′:6′,2″-terpyridine derivatives are reported herein. The UV-Vis spectra in acetonitrile as well as in dichloromethane show two intense bands in the UV areas 252–262 nm and 275–290 nm while the fluorescence emission spectra are only slightly influenced by chemical derivatization.