Syntheses, structures, and properties of metal complexes involving π-conjugated tetrathiafulvalene-pyridine ligand

Four metal complexes based on the phenyl-bridged pyridine ligand with tetrathiafulvalene unit (TTF-Ph-Py, L), Ni^II(acac)₂(L)₂ (1, acac = acetylacetonate), M(hfac)₂(L)₂ (M = Ni^II, 2; M = Cu^II, 3; hfac = hexafluoroacetylacetonato) and [Co^II(Tp^Ph2)(OAc)(L)]·H₂O (4, Tp^Ph2 = hydridotri(3,5-diphenylpyrazol-1-yl) borate), have been synthesized and structurally characterized. The absorption spectra and redox behaviors of these new compounds have been studied. Optimized conformation and molecular orbital diagram of L has been calculated with density functional theory (DFT).     

Biradical character of linear π-conjugated oligomer dications composed of thiophene, pyrrole, and methylthio end-capping units

Combined DFT calculations and UV-vis-NIR, ESR, and SQUID measurements revealed that the ground-state electronic structure of a linear π-conjugated oligomer dication composed of two pyrrole and six or seven thiophene rings and methylthio end-capping units is dominated by a singlet biradical character.     

Quantum-coherence and correlations in π-conjugated molecules and multichromophoric systems

Chemistry is intrinsically founded on quantum mechanical principles and examples of quantum-mechanical phenomena abound on a range of energy and length scales. In this article some examples of quantum-mechanical phenomena that can be probed by optical spectroscopy are discussed. Recent experimental studies of quantumcoherence in electronic energy transfer in π-conjugated polymers are reported as examples of weak correlations. The nature of the electron-hole binding energy for excitons in organic systems is investigated as a case of intermediate correlations. Possible experimental probes of strong correlations involved in chemical reactions are critically examined in the final section of the paper.     

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.     

Chemical sensors based on π-conjugated organic molecules and gold nanoparticles

Scientists have developed techniques for synthesizing and characterizing many new materials including conjugated small molecules, polymers and gold particles protected by conjugated organic chromophores for testing specific sensing properties in the past decade. Still, the design and synthesis or supermolecular systems fabrication of novel materials with controlled sensing properties is a significant and ongoing challenge within nanoscience and nanotechnology. Recently, our group has successfully constructed a series of chemosensors using small organic molecules, conjugated polymers and gold nanoparticles for real-time detection of specific analytes. The chemosensors show high selectivity and sensitivity in the detection of cations and biologic analytes and thus are potentially promising for applications in sensing assay system. In this review, recent sutdies on the design, synthesis and photo-physical properties of novel materials and construct of chemosensors are summarized with an emphasis on the development in our groups in recent years. Supported by the National Natural Science Foundation of China (Grant Nos. 20531060, 20721061 & 20873155), and the National Basic Research 973 Programme of China (Grant No. 2007CB936401)     

Noncovalent wrapping of chemically modified graphene with π-conjugated disk-like molecules

A facile and scalable preparation of dispersion of isolated graphene in various organic solvents has been developed by combining between covalent and noncovalent functionalizations of the graphene surface. Covalently functionalized graphene (FRG) was prepared by the reaction of partially reduced graphene oxide with aryl diazonium salts, followed by the graphene oxide being completely reduced with hydrazine. The resulting FRG disperse readily in organic solvents such as N,N′-dimethylformamide (DMF) and N-methyl-2-pyrrolidinone and the functionalization of graphene was characterized by Fourier transform infrared spectroscopy, thermogravimetric thermogram, X-ray photoelectron spectroscopy, and Raman spectroscopy. The hydrophobic surface of FRG was noncovalently wrapped with aromatic hexakis-dodecylhexa-peri-benzocorone (HBC) by simply mixing of dispersion of FRG in DMF with toluene solution of HBC. The complexation of FRG and HBC was monitored by viewing the absorption and fluorescence spectral changes. Atomic force microscopic images confirmed that graphene was covalently and noncovalently functionalized, while keeping a two-dimensional sheet shape.     

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).     

Accessing π-expanded heterocyclics beyond dibenzothiophene: Syntheses and properties of phenanthrothiophenes

A series of phenanthrothiophenes are designed and synthesized from polyarylthiophenes through regioselective Scholl reactions in one step using iron chloride as catalyst. The molecular structures of these heteroarenes displayed multiple twisted fjords, which perturb the shapes of the polycyclic frameworks to pack in slipped to near-perfect face-to-face styles in parallel or antiparallel packings. Field-effect transistor devices using single crystals of 6,12-difluorodiphenanthro[9, 10-b:9′, 10′]thiophene gave a hole mobility of 0.22 cm² V⁻¹ s⁻¹.     

Pyridine-cored V-shaped π-conjugated oligomers: synthesis and optical properties

A new series of V-shaped pyridine-cored π-conjugated oligomers are synthesized utilizing two-fold Heck/Suzuki coupling reactions. Optical properties of these compounds (λ_max=390–449 nm, Φ_fl=79–5%, in solutions) are discussed. They are shown to be thermally stable and soluble in common organic solvents. Stilbenoid oligomers exhibited much higher fluorescence quantum yields than tri- and tetra-phenylethylene substituted oligomers in solutions.     

Titanylation and vanadylation of highly π-conjugated porphyrins

We report the efficient synthesis of tetrabicycloporphyrin titanyl and vanadyl without decomposition of the bicyclo[2.2.2]octadiene unit. The complexes were heated under vacuum to give titanyl and vanadyl tetrabenzoporphyrins in 100% yield. We also titanylated and vanadylated tetra[2,3]naphthoporphyrin and tetra[2,3]anthraporphyrin, which have a greater degree of π conjugation than tetrabenzoporphyrin.     

Chemical-stimuli-controllable circularly polarized luminescence from anion-responsive π-conjugated molecules

Introduction of a BINOL-boron moiety to dipyrrolyldiketones as precursors of anion-responsive π-conjugated molecules results in the formation of a chiral environment in the form of anion-free receptors and anion-binding complexes. Conformation changes by inversion (flipping) of two pyrrole rings as a result of anion binding can control the chiroptical properties of the anion receptors. In particular, appropriate pyrrole β-substituents induce distorted receptor π-planes and, as a result, give larger circularly polarized luminescence (CPL), which can be tuned by chemical stimuli (anions). This is the first example of chemical-stimuli-responsive CPL properties.     

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 1,2,5,6- and 1,4,5,8-anthracenetetrone: Building blocks for π-conjugated small molecules and polymers

Reliable reactions for the synthesis of two interesting anthracenetetrones have been identified and optimized. Both syntheses start from dihydroxy-9,10-anthraquinones and were selected for maximized efficiency and minimized workload. Work-up of all reactions can be achieved without column chromatography, which facilitates further scale-up. So far, both target compounds are considerably underexplored despite their promising molecular structure for use in devices and in organic synthesis, especially as building blocks for π-conjugated compounds. The crystal structure of 1,4,5,8-anthracentetrone is reported.     

Electrochemical properties of new n-type π-conjugated polybipyridines and polybiphenylenes with various bridging units

New electrochemically active π-conjugated polymers were prepared. They had polybipyridine or polybiphenylene type structure with an –NN–, –O–, or –NHCONH– bridging group between the two aromatic units, and underwent more facile electrochemical reduction (or n-type doping) than the mother π-conjugated polymers without the bridging group.     

Two-photon absorption properties of two-dimensional π-conjugated chromophores: combined experimental and theoretical study

The two-photon absorption (TPA) properties of four TPEB [tetrakis(phenylethynyl)benzene] derivatives (TD, para, ortho, and meta) with different donor/acceptor substitution patterns have been investigated experimentally by the femtosecond open-aperture Z-scan method and theoretically by the time-dependent density-functional theory (TDDFT) method. The four compounds show relatively large TPA cross sections, and the all-donor substituted species (TD) displays the largest TPA cross-section σ(2) = 520 ± 30 GM. On the basis of the calculated electronic structure, TD shows no TPA band in the lower energy region of the spectrum because the transition density is concentrated on particular transitions due to the high symmetry of the molecular structure. The centrosymmetric donor-acceptor TPEB para shows excitations resulting from transitions centered on D-π-D and A-π-A moieties, as well as transition between the D-π-D and A-π-A moieties; this accounts for the broad nature of the TPA bands for this compound. Calculations for two noncentrosymmetric TPEBs (ortho and meta) reveal that the diminished TPA intensities of higher-energy bands result from destructive interference between the dipolar and three-state terms. The molecular orbitals (MOs) of the TPEBs are derivable with linear combinations of the MOs of the two crossing BPEB [bis(phenylethynyl)benzene] derivatives. Overall, the characteristics of the experimental spectra are well-described based on the theoretical analysis.     

Effects of hyperbranched and linear architecture on properties of polymers composed of poly(ɛ-caprolactone) and hydroxycinnamic acid

Photoreactive and degradable polymers with linear and hyperbranched architectures which composed of poly(?-caprolactone) and hydroxycinnamic acid or its substituted derivatives were synthesized by thermal melt-polycondensation. The chemical structures of the polymers were confirmed by FTIR and ¹H NMR measurements. The polymers showed good photoreactivities and fluorescent properties, and the hyperbranched polymers showed higher photoreactive speed and weaker fluorescence properties. These polymers had excellent thermal stabilities due to the rigid conjugated structures and the π-π strcking interaction of the cinnamoyl group, especially for the hyperbranched polymer. Moreover, the hydrolysis experiments and the XRD results revealed that the hyperbranched and linear polymers are amorphous and crystalline, respectively, and the degradation rate of amorphous polymers are faster than crystalline samples.     

Synthesis of π-conjugated molecules based on 3,4-dioxypyrroles via Pd-mediated decarboxylative cross-coupling

A general scheme for the synthesis of π-conjugated molecules based on 3,4-dioxypyrroles is presented. The π-conjugated molecules were synthesized via Pd-mediated decarboxylative cross-coupling using various 3,4-propylenedioxypyrrole carboxylic acids and aryl bromides, including the base-sensitive electron acceptor 4,7-dibromobenzo[c][1,2,5]thiadiazole (BTD). N-Methylpyrrolidone was used as solvent, Pd(acac)(2) was employed as the palladium source and P(o-tol)(3) as the ligand. The methodology was applied to 3,4-dioxypyrrole monoacids and 3,4-dioxypyrrole diacids to produce multi-ring π-conjugated systems containing phenyl, thiophenyl, BTD, and pyridinyl units. In general, the method has yielded a practical approach for the synthesis of 3,4-dioxypyrrole-based π-conjugated molecules in acceptable to high yields of 44-94%.     

DNA-templated assembly of dyes and extended π-conjugated systems

This feature article reports on the use of DNA as a template to assemble dyes and π-conjugated systems with the aim to construct functional multicomponent nanostructures that have a well-defined size, shape and sequence.     

Synthesis of extended, π-conjugated isoindolin-1-ones

The synthesis and characterization of extended, conjugated molecules containing isoindolinone units was explored. Nucleophilic cyclizations between an amide and an alkyne were found to be an efficient method of producing the desired isoindolin-1-ones in high yields. A variety of derivatives were synthesized, demonstrating that a number of structural alterations could be made while maintaining good regio- and stereospecificity in the cyclized product.     

Synthesis and properties of π-conjugated donor–acceptor macrocycles derived from phenanthrylene building blocks

Phenanthrylene-ethynylidene macrocycles combining electron donor and electron acceptor subunits in their shape-persistent fully conjugated core were synthesized. The donor subunits consisted of two 9,10-dialkoxyphenanthrenes linked either with 1,2-ethynylidene or 2,5-thienylene bridge. The acceptors were 9,10-phenanthroquinone and dibenzoquinoxaline and dibenzophenazines derived from it. Solvatochromic photoluminescence from intramolecular-charge-transfer (ICT) excited state was observed mainly in non-polar solvents. In more polar solvents, the excited states favor non-radiative relaxation. DFT calculated HOMO/LUMO energies of the macrocycles correlate well with spectroscopic and electrochemical data. In the series of substituted dibenzophenazine acceptors a good correlation with Hammett substituent constants σ_p^– was found.