Synthesis and properties of thiophene-functionalized π-extended tetrathiafulvalenes

Two molecular ensembles composed of an array of thiophene-extended tetrathiafulvalene-thiophene were synthesized using Stille coupling and Horner-Wittig reaction as the key steps. Electrochemical redox and electronic absorption properties were investigated by voltammetric and UV-vis spectroscopic analyses.     

Cycloaddition to a C3-ethynylated chlorophyll derivative and self-aggregation of zinc chlorin–pyrazole/triazole conjugates

Several kinds of cycloaddition reactions were applied to C3-ethynylated pyropheophorbide-a methyl ester to develop C3-functionalized chlorophyll derivatives. Its [2+2] cycloaddition with tetracyanoethylene, [2+3] cycloaddition with diazomethane, [2+3] Huisgen reaction with trimethylsilyl azide, and [2+4] Diels–Alder reaction with tetraphenylcyclopentadienone gave the expected products in moderate to high yields. Zinc complex of the resulting 3-pyrazolyl-chlorin was found to show self-aggregation in a less polar solvent, in an aqueous micelle, and in the solid thin films more readily than the corresponding zinc 3-triazolyl-chlorin.     

Synthesis and properties of conjugated oligoyne-centered π-extended tetrathiafulvalene analogues and related macromolecular systems

Alkynyl-substituted phenyldithiafulvenes have been found to act as versatile building blocks for the construction of π-conjugated molecular rods, shape-persistent macrocycles (SPMs), and conducting polymers. Through Cu(I)-catalyzed alkynyl homocoupling, a series of linear-shaped π-extended tetrathiafulvalene analogues (exTTFs) carrying conjugated oligoynes (ranging from diyne to hexayne) as the central π-bridge were readily prepared. The solid-state properties and reactivities of diyne- and tetrayne-centered exTTFs were characterized by X-ray crystallography and differential scanning calorimetry (DSC), while the electronic properties of the oligoyne-exTTFs were elucidated by UV-vis absorption spectroscopy and density functional theory (DFT) calculations. Cyclic voltammetric analysis showed that the terminal phenyldithiafulvene groups of the oligyne-exTTFs could undergo oxidative coupling to form tetrathiafulvalene vinylogue (TTFV)-linked polymer wires. Through a different synthetic route involving oxidative dimerization and Pd/Cu-catalyzed alkynyl homocoupling, the acetylenic phenyldithiafulvene precursors led to shape-persistent macrocycles where the formation of trimeric macrocycles was particularly favored due to the small ring strain incurred. Finally, spectroelectrochemical studies on these oligoyne and TTF hybrid materials disclosed electrochromic and molecular redox-controlled switching properties applicable to molecular electronic and optoelectronic devices.     

Photophysical and electrochemical properties of π-extended molecular 2,1,3-benzothiadiazoles

The reaction of 4,7-dibromo-2,1,3-benzothiadiazole with arylboronic acids (phenyl, 1-naphthyl, 4-methoxyphenyl, 4-chlorophenyl and 4-trifluoromethylphenyl) in the presence of catalytic amounts of a NCP-pincer palladacycle affords photoluminescent π-extended 4,7-diaryl-2,1,3-benzothiadiazoles 4a-e in high yields. These 4,7-diaryl-2,1,3-benzothiadiazoles exhibit high fluorescent quantum yields, high electron affinities and adequate band gap values for testing as OLEDs. The 4,7-bis-naphthyl-2,1,3-benzothiadiazole 4b presents two different lifetimes (bi-exponential decay) due to the presence of two atropisomers. The Sonogashira coupling reaction of 4,7-diethynyl-2,1,3-benzothiadiazole 6 with the corresponding halo-aryl compounds (iodobenzene, 1-bromonaphthalene, 4-iodoanisole, 4-bromo-N,N-dimethylaniline and 2-bromopyridine) afforded the photoluminescent π-extended 4,7-bis-alkynylaryl-2,1,3-benzothiadiazoles 7a-e, also in high yields. These 4,7-diethynyl-2,1,3-benzothiadiazoles also present high fluorescent quantum yields, high electron affinities and adequate band gap values for testing as OLEDs. The 4,7-disubstituted-2,1,3-benzothiadiazoles 4a-e and 7a-e exhibit different electrochemical behavior. The presence of two ethynyl spacers in 2,1,3-benzothiadiazoles 7a-e shifts the reduction potentials to less cathodic values and also results in two well-defined and distinct reduction processes.     

Synthesis of a π-extended TTF-perylenediimide donor-acceptor dyad

A donor-acceptor dyad containing perylenediimide as the electron acceptor and π-extended tetrathiafulvalene as electron donor has been successfully synthesized by means of a Wittig reaction. Cyclic voltammetry and absorption spectroscopy show that both electroactive units preserve their nature, whereas preliminar photophysical investigations show a strong fluorescence quenching.     

Synthesis and properties of [9]cyclo-1,4-naphthylene: a π-extended carbon nanoring

The first synthesis of a π-extended carbon nanoring, [9]cyclo-1,4-naphthylene ([9]CN), has been achieved. Careful structure-property analyses uncovered a number of unique features of [9]CN that are quite different from those of [9]CPP, a simple carbon nanoring.     

Conformational and spectroscopic properties of π-extended, bipyrrole-fused rubyrin and sapphyrin derivatives

Two new expanded porphyrins, naphthorubyrin and naphthosapphyrin, were synthesized. The π-extended rubyrin was isolated and structurally characterized in its monoprotonated form. The sapphyrin congener undergoes pyrrole inversion as a function of the protonation state. These conformational effects are reflected in the spectroscopic features, including the excited singlet state lifetimes.     

Synthesis and optical properties of π-conjugated polymers and oligomers bearing hexaphenylbenzene and tetraphenyl ethene units

π-Conjugated polymers (CPs) and oligomers (COs) bearing hexaphenylbenzene (HPB) and tetraphenyl ethene (TPE) units were synthesized by Sonogashira and Suzuki–Miyaura coupling reactions. The optical properties of the CPs and COs were investigated by UV–vis, photoluminescence (PL), and fluorescence lifetime (τ) measurements. The PL intensities of the solutions of the CPs and COs synthesized by Sonogashira coupling were reduced upon addition of poor solvent like water, which is attributed to aggregation-caused quenching. In contrast, the CP and COs bearing the TPE unit synthesized by Suzuki–Miyaura coupling exhibited aggregation-induced emission enhancement in solution. This difference in fluorescence behavior is discussed herein in terms of the molecular sizes, conformations in solution, and τ values of the CPs and COs.     

Synthesis of π-extended porphyrins via intramolecular oxidative coupling

Porphyrins fused with other aromatic units at the meso- and β-positions have recently emerged as a hot topic of research. Their synthesis typically starts with preparation of precursors via either Suzuki coupling of a meso-bromoporphyrin or mixed-aldehyde condensation, and is followed by oxidative aromatic coupling, often using high-valent metal reagents (DDQ/Sc(OTf)(3) and Fe(iii) salts are among the most popular). In recent years, porphyrins were oxidatively coupled not only with well-known aromatic hydrocarbons such as naphthalene and pyrene, but also with more complex heterocyclic fragments, including indole, phenanthro[1,10,9,8-cdefg]carbazole and BODIPY. A subtle relationship exists between the output of intramolecular oxidative coupling and the nature of the second aromatic moiety, cation in the porphyrin cavity, oxidant, and type of remaining meso-substituent. The extension of the porphyrin chromophore leads to significant change in linear and non-linear optical properties. Very strong bathochromic shifts of absorption (λ(max) reaching 1.5-2 microns in some cases) and increases in two-photon absorption cross-sections are typical for these functional dyes.     

Synthesis and spectral properties of π-extended rhodamine hydrazide probe for the detection of Hg2+EI北大核心CSCD

The π-extended rhodamine derivative aminobenzopyranoxanthene ABPX was synthesized by condensation of 2-4-diethylamino-2-hydroxybenzoylbenzoic acid with resorcinol in H2 SO4 solutionthen the derivative reacted with hydrazine monohydrate to obtain ABPX-hydrazideABPX-hyand its structure was characterized by ESI-MSFT-IR and NMR spectroscopy. The UV-Vis adsorption spectra at 500-600 nm tended to increase in the presence of Hg2+ in ABPX-hy ethanol solutionand the color of the solution changed from colorless to pink and gradually deepenedenabling visual colorimetric detection of Hg2+ by naked eye. Under the coexistence of 10 common metal ionsthe recognition of Hg2+ at 533 nm showed good anti-interference sensing performance. The absorption intensity of ABPX-hy had a good exponential relationship with the addition of Hg2+. The continuous coordination of Hg2+ to the N and O binding sites of ABPX-hy formed 21 stoichiometry of the ABPX-hy-Hg2+ complex. The orbital energy and spatial distribution levels of the closed-cycle to the open-cycle form were obtained by density functional theoryDFTcalculation. © 2022, Youke Publishing Co.,Ltd. All rights reserved.     

Synthesis and physical properties of π-conjugated metallacycle polymers of cobalt and ruthenium

Recent studies on two types of π-conjugated metallacylce polymers are reviewed. Reaction of CpCo(PPh₃)₂ with conjugated diacetylenes afford poly(arylene cobaltacyclopentadienylene) and that of CpRuBr(cod) does poly(arylene ruthenacyclopentrienylene)s in ambient conditions. Regioselectivity of the former metallacycling reacion is not perfect (at most 80% of the 2,5-diaryl selectivity) but that of the latter is satisfactory (∼100% of the 2,5-diaryl selectivity) for the formation of π-conjugated structure. Electrochemical oxidation of the cobaltacyclopentadiene polymer and reduction of the ruthenacycle polymer occur facilely and quasi-reversibly by the contribution of metal d-orbitals. Physical properties in undoped (neutral) and doped (charged) sates show the behavior of electronic band structure derived from the organic π-conjugated main chain strongly coupled with the metal d-orbitals. This affords, for example, photoconductivity in the neutral form of the cobaltacylopentadiene polymer and ferromagnetic interaction in the reduced form of the ruthenacyclopentatriene polymer.     

Synthesis and characterization of π-extended thienoacenes with up to 13 fused aromatic rings

π-Extended thienoacenes that comprise alternatively arranged anthracene and thieno[3,2-b]thiophene moieties and have 8 or 13 aromatic rings were synthesized. The delocalization of their HOMO and LUMO orbitals is over the entire molecules, and low-lying HOMO levels endow them good stability.     

Synthesis and nonlinear optical properties of linear and Λ-shaped pyranone-based chromophores

New, pyranone-based chromophores were synthesized and their (nonlinear) optical properties were measured. The chromophores were prepared by first condensing an electron withdrawing group with pyranone, followed by reaction with an aldehyde-functionalized π-conjugated bridged donor molecule. This approach enables one to easily incorporate the pyranone moiety and to prepare both linear and Λ-shaped chromophores. The (nonlinear) optical properties were measured using femtosecond hyper-Rayleigh scattering. These measurements demonstrated the advantages of this approach.     

Synthesis and properties of covalently linked BF2–oxasmaragdyrin–porphyrin dyads and triad

Two covalently linked diphenyl ethyne bridged unsymmetrical dyads containing porphyrin and BF₂–oxasmaragdyrin and Zn(II)porphyrin and BF₂–oxasmaragdyrin units and one covalently linked triad containing Zn(II)porphyrin, porphyrin and BF₂–oxasmaragdyrin units were synthesized by coupling appropriate functionalized macrocycles under Pd(0) coupling reaction conditions. The dyads and triad were freely soluble in common organic solvents and confirmed by ES-MS spectra. 1D and 2D NMR techniques were used to characterize the dyads and triad. Absorption and electrochemical studies of dyads and triad showed the overlapping features of the constituted macrocycles indicating that the macrocycles retain their basic features in the dyads and triad. The BF₂–oxasmaragdyrin absorbs at lower energy and emits strongly in the visible region compared to porphyrin/Zn(II)porphyrin. Thus, BF₂–oxasmaragdyrin acts as energy acceptor and porphyrin/Zn(II) porphyrin act as energy donor in dyads and triad. The steady state and time-resolved fluorescence studies supported an efficient energy transfer from porphyrin/Zn(II)porphyrin to BF₂–oxasmaragdyrin unit in dyads and triad.     

Synthesis and characterization of β-fused porphyrin-BODIPY dyads

Novel dyads in which a porphyrin ring is directly fused through two β-pyrrolic carbons to a BODIPY^® moiety have been prepared using a stepwise approach starting from the copper(II) complex of pyrrolo[2,3-c]-5,10,15,20-tetraphenylporphyrin. Formylation and reaction with 3,5-dimethylpyrrole afforded 8; subsequent BF₂ complexation gave the TPP-BODIPY^® dyad in reasonable yields. Demetalation in TFA/H₂SO₄ led to the corresponding free base 12, opening the way to the subsequent preparation of the Zn complex 13. Both 12 and 13 exhibited complex optical spectra with an intensely red-shifted Q-band. Luminescence spectra displayed a very intense band around 700 nm making these species suitable as near-IR dyes and sensors in biological media. Optical analyses of 12, using the INDO/SCI technique, were performed to obtain information to establish the origin of the novel optical properties. These studies showed that the optical properties of 12 cannot be attributed to deformation of the molecular skeleton, but derive from the increased extension of the conjugation between the TPP and BODIPY^® π-systems.     

Synthesis and photo-physical properties of methoxy-substituted π-conjugated-2,2′-bipyridines

4,4′-Bis-vinyl-2,2′ bipyridines have been known in the area of materials chemistry since last few decades. Bipyridine molecules bearing donor substituents in their π backbone are examples of ‘push-pull’ molecules. Emissive properties of such ligands depend on the position of the donor unit in their π backbone. The Horner-Wordsworth-Emmons reaction has been used extensively to synthesize such types of conjugated systems. Three newly synthesized highly conjugated 2,2′ bipyridines (3a-c) have been described. The molecules 3a-c are highly emissive in the visible region at room temperature.     

Synthesis of C3-nitroalkylated-4-hydroxycoumarin and hydroxyiminodihydrofuroquinolinone derivatives via the Michael addition of cyclic 1,3-dicarbonyl compounds to β-nitrostyrenes

Herein, we describe a practical and efficient method for the C3-alkylation of 4-hydroxycoumarin by sonication under ‘on water’ conditions and mild temperatures using various substituted β-nitrostyrenes. In addition, we report on the development of a convenient process for the regioselective synthesis of angular hydroxyiminodihydrofuroquinolinone catalyzed by base. 4-Hydroxycoumarin and 4-hydroxy-1-methylquinolin-2(1H)-one reacted smoothly with various nitroolefins to furnish C3-nitroalkylated hydroxycoumarin derivatives (by sonication and ‘on water’ conditions) and hydroxyiminodihydrofuroquinolinone derivatives (ambient condition) as a mixture of Z (minor) and E (major) isomers, respectively. The mild reaction conditions employed, ease of isolation of the products and excellent yields constitute important features of the methodology.     

Synthesis and photophysical properties of aryl-substituted 2-borylbenzaldimines and their extended π-conjugated congeners

Novel N-aryl-substituted 2-borylbenzaldimines 6 and related systems with extended π-framework 7 based on two borylbenzaldimine units linked by a spacer moiety were synthesized by condensation reactions of 2-(dimesitylboryl)benzaldehyde 3 with various amines 4 and diamines 5. All compounds were completely characterized including X-ray diffraction, especially in view of Lewis acid-base B-O and B-N interactions. The electronic as well as the photophysical properties of bisimines 7 were determined using cyclic voltammetry, UV/vis, and fluorescence spectroscopy and quantum chemistry. These compounds feature large Stokes shifts and reversible reduction waves. Interestingly, UV irradiation experiments unfold enhanced photostability for compounds 7 with an extended π-skeleton. By use of 1,8-diaminonaphthalene we observed the formation of a hitherto unknown BN-heterocyclic compound 9 fused with a perimidine skeleton. Structural and energetic aspects were evaluated by high level quantum chemical methods (DFT and SCS-MP2-calculations).     

Synthesis and photophysical properties of heptamethine cyanine–fullerene C60 dyads with non-quenched fluorescence

Two new heptamethine cyanine dye–fullerene C₆₀ covalently- linked dyads, which absorb in far-red and NIR spectral regions, have been synthesized by esterification click reaction and characterized by physicochemical methods. No significant fluorescence quenching was found due to weak electronic coupling between heptamethine moiety and fullerene core, which was confirmed by photophysical and electrochemical methods. Such dyads can be useful for cell imaging and fluorescence diagnostics of various fullerene derivatives.