Π-conjugated Moieties Research Articles

Panchromatic π-Extended Porphyrins from Conjugation with Quinones.

Typical porphyrins are coloured compounds due to their characteristic wavelength-selective visible light absorptions. An exceptional "blackened" ZnII -porphyrin was recently obtained from fusing the β,β'-positions of the porphyrin core with four quinone units. Here, studies with metal-free and NiII -containing analogues are reported. These quinone-fused porphyrins were prepared from the corresponding β,β'-tetrasulfolenoporphyrins via thermally generated porphyrindienes, which were trapped by [4+2] cycloaddition as benzoquinone cycloadducts, which were subsequently oxidised. By using this strategy, metal-free and NiII -containing porphyrins with one, two, three or four conjugated naphthoquinone moieties were prepared efficiently. The presence of the π-conjugated naphthoquinone moieties changed the porphyrin chromophores profoundly, giving broadly absorbing "blackened" pigments. The influence of coordinated NiII ions, or of the absence of a metal ion in the modified porphyrin core, on their structural and spectroscopic properties was explored. Blackened quinone-conjugated porphyrins might be pigments suitable for solar energy conversion. With their unique peripheral functional groups they are also a set of porphyrins "programmed" for further covalent extension. Thus, they are building blocks for the preparation of supra-porphyrinoid assemblies that might be useful in optoelectronics and in the nanosciences.

Naphthalene‐Functionalized, Photoluminescent Room Temperature Ionic Liquids Bearing Small Counterions

Obtaining π-conjugated room temperature ionic liquids (RTILs) is difficult because of the relatively strong π-π interaction among the π-moieties. Existing strategies by using bulky counterions greatly hindered further property optimization and potential applications of these intriguing functional fluids through simple ion exchange. Herein, four naphthalene-functionalized, π-conjugated RTILs with small counterions (Br(-) ) have been facilely synthesized with high yields. Our strategy is to attach branched alkyl chains to the cationic backbone of the target compounds (2 a-d), which effectively tune inter- and intramolecular interactions. Compounds 2 a-d have satisfactory thermal stability (up to 300 °C) and low melting points (<-19 °C). Rheological measurements revealed the fluid character of 2 a-d, whose viscosity decrease with the increase of the alkyl chain length and temperature. The presence of the π-conjugated naphthalene moiety imparts 2 a-d photoluminescent properties in bulk solutions. Moreover, the absence of strong π-π stacking among the naphthalene units in solvent-free states enables them to be used as a new generation of photoluminescent inks.

Tuning charge transport from unipolar (n-type) to ambipolar in bis(naphthalene diimide) derivatives by introducing π-conjugated heterocyclic bridging moieties

The charge transport polarity of a series of acceptor–donor–acceptor (A–D–A) conjugated molecules can be tuned from unipolar (n-type) to ambipolar.

Synthesis, morphology, and electrical memory application of oligosaccharide-based block copolymers with π-conjugated pyrene moieties and their supramolecules

Transistor memory applications of maltoheptaose-block-poly(1-pyrenylmethyl methacrylate), and their supramolecules with (4-pyridyl)-acceptor-(4-pyridyl).

Interaction of Iron II Complexes with B-DNA. Insights from Molecular Modeling, Spectroscopy, and Cellular Biology.

We report the characterization of the interaction between B-DNA and three terpyridin iron II complexes. Relatively long time-scale molecular dynamics (MD) is used in order to characterize the stable interaction modes. By means of molecular modeling and UV-vis spectroscopy, we prove that they may lead to stable interactions with the DNA duplex. Furthermore, the presence of larger π-conjugated moieties also leads to the appearance of intercalation binding mode. Non-covalent stabilizing interactions between the iron complexes and the DNA are also characterized and evidenced by the analysis of the gradient of the electronic density. Finally, the structural deformations induced on the DNA in the different binding modes are also evidenced. The synthesis and chemical characterization of the three complexes is reported, as well as their absorption spectra in presence of DNA duplexes to prove the interaction with DNA. Finally, their effects on human cell cultures have also been evidenced to further enlighten their biological effects.

DPP containing D–π–A organic dyes toward highly efficient dye-sensitized solar cells

Two diketopyrrolopyrrole (DPP) containing D–π–A organic dyes, named as TEDBn and TEDTh were prepared. Their optical, electrochemical and photophysical properties were investigated and their application in dye-sensitized solar cells (DSCs) was demonstrated. The broaden absorption and low-energy λmax of DPP containing dyes were contributed from DPP bridge and EDOT π-conjugated moiety. Compared to TEDTh, TEDBn has smaller absorption coefficient and higher optical bandgap. Nevertheless the power conversion efficiency (PCE) of TEDBn based DSC is 7.2% which is larger than that of TEDTh based DSC and 90% of N719 based cell. The higher PCE of TEDBn based device originates from both higher open-circuit voltage (VOC) and short-circuit current (JSC). Femtosecond time-resolved photoluminescence data show that the electron injection at TEDBn/TiO2 is more efficient than that at TEDTh/TiO2 interface, resulting in higher JSC (and IPCE) of TEDBn based DSC. Density function theory (DFT) calculations revealed that TEDBn is a linear structure which leads to higher dye loading on TiO2 than TEDTh which featured a bend conformation, better TiO2 surface coverage, resulting in larger VOC. Therefore, the overall efficiency of the cell sensitized by TEDBn is better than that the devices based on TEDTh.

Terminal modification of polymeric micelles with π-conjugated moieties for efficient anticancer drug delivery

High drug loading content is the critical factor to polymeric micelles for efficient chemotherapy. Small molecules of cinnamic acid, 7-carboxymethoxy coumarin and chrysin with different π-conjugated moieties were immobilized on the terminal hydroxyl groups of PCL segments in mPEG-PCL micelles to improve drug loading content via the evocation of π-π stacking interaction between doxorubicin (DOX) and polymeric micelles. The modification of π-conjugated moieties enhanced the capability of crystallization of mPEG-PCL block copolymers. The drug loading content increased dramatically from 12.9% to 25.5% after modification. All the three modified mPEG-PCL micelles were nontoxic to cells. Chrysin modified polymeric micelles exhibited the most efficient anticancer activity. The in vivo anticancer activity of 10 mg/kg DOX dose of chrysin modified micelle formulation for twice injections was comparable to that of 5 mg/kg dose of free DOX·HCl for four injections under the circumstance of same total DOX amount. The systemic toxicity of DOX loaded chrysin modified micelles was significantly reduced. This research provided a facile strategy to achieve polymeric micelles with high drug loading content and efficient anticancer activity both in vitro and in vivo.

Anion Recognition Triggered Nanoribbon-Like Self-Assembly: A Fluorescent Chemosensor for Nitrate in Acidic Aqueous Solution and Living Cells.

A water-soluble π-conjugated bispyridinium phenylenevinylene-based fluorogenic probe has been developed as a novel fluorescent chemosensor for highly selective, sensitive, and rapid detection of NO3(-) anion in acidic aqueous media. This system self-assembles to a nanoribbon as a result of ionic interaction. The positively charged chemosensor generates a nearly instantaneous significant fluorescence signal (475 vs 605 nm) in response to NO3(-) in the green/yellow spectral region, with a large Stokes shift (130 nm). The fluorescence changes can be attributed to the self-aggregation of the sensor triggered by ionic interaction, which occurs as a consequence of the subtle cooperation of electrostatic ionic bonding, van der Waals forces, and π-stacking of the π-conjugated aromatic moieties. Importantly, this chemosensor has been employed for the first time for the fluorescence detection of intracellular NO3(-) anion in cultured cells.

Synthesis of Oligosaccharide-Based Block Copolymers with Pendent π-Conjugated Oligofluorene Moieties and Their Electrical Device Applications

We report the synthesis and electric device applications of oligosaccharide-based diblock copolymers consisting of a maltoheptaose (MH) block and a poly(4-oligofluorenylstyrene) block (PStFln, n = 1 or 2), referred to as MH-b-PStFln. MH-b-PStFln was prepared by the Cu(I)-catalyzed click reaction of azido-terminated PStFln (PStFln-N3), which was obtained from the azidation reaction of the bromo-terminated PStFln (PStFln-Br), with excess ethynyl-terminated MH in the THF/DMF mixture solvent. The resulting diblock copolymers self-assembled to spherical microdomains with sub-10 nm sizes in both bulk and thin film state after annealing process. Thereafter, the MH-b-PStFln thin film (∼50 nm) with the self-assembled nanoscale spherical aggregates was used as the charge storage layer for the pentacene-based field-effect transistor type memory devices. The MH-b-PStFln-based devices had the excellent hole mobility (0.25–0.52 cm2 V–1 s–1) and the high ON/OFF current (ION/IOFF) ratio of 107–108, of which the MH-b-PStF...

Nonvolatile transistor memory devices based on high-k electrets of polyimide/TiO2hybrids

Novel nonvolatile memory behaviors of n-type N,N′-bis(2-phenylethyl)-perylene-3,4,9,10-tetracarboxylic diimide (BPE-PTCDI) based organic field-effect transistors (OFET) using the new polyimides (PIs), (poly[9,9-bis(4-(4-amino-3-hydroxyphenoxy)phenyl)fluorene-oxydiphthalimide]) PI(F-ODPA) and (poly[4,4′-bis(4-amino-3-hydroxyphenylthio)diphenyl sulfide-oxydiphthalimide]) PI(3S-ODPA), and their PI/TiO2 hybrids as electrets are reported. The OFET memory devices derived from PI(F-ODPA) with π-conjugated fluorene moieties exhibited a larger memory window (8.6 V), and could be further enhanced by introducing TiO2 (up to 20 wt%) into the PIs. In addition, PI/TiO2 hybrids as electrets for memory devices also could effectively reduce the operating voltage, indicating that the charge transfer capability of TiO2 plays an important role in transferring and storing the charge for OFET memory devices.

Adjusting the Local Arrangement of π-Stacked Oligothiophenes through Hydrogen Bonds: A Viable Route to Promote Charge Transfer

We show that substituting quaterthiophene cores with strong H-bond aggregators, such as urea groups, provides an efficient way to adjust the mutual in-plane displacements of the semiconducting units and promote charge transfer. Our 2-D structure–property mapping reveals that the insertion of substituents induces up to 2.0 Å longitudinal and transversal displacements between the π-conjugated moieties. Some of these relative displacements lead to improved cofacial orbital overlaps that are otherwise inaccessible due to Pauli repulsion. Our results also emphasize that the fine-tuning of in-plane displacements is more effective than achieving “tighter” packing to promote charge-transfer properties.

Digital memory versatility of fully π-conjugated donor-acceptor hybrid polymers.

The fully π-conjugated donor-acceptor hybrid polymers Fl-TPA, Fl-TPA-TCNE, and Fl-TPA-TCNQ, which are composed of fluorene (Fl), triphenylamine (TPA), dimethylphenylamine, alkyne, alkyne-tetracyanoethylene (TCNE) adduct, and alkyne-7,7,8,8-tetracyanoquinodimethane (TCNQ) adduct, were synthesized. These polymers are completely amorphous in the solid film state and thermally stable up to 291-409 °C. Their molecular orbital levels and band gaps vary with their compositions. The TCNE and TCNQ units, despite their electron-acceptor characteristics, were found to enhance the π-conjugation lengths of Fl-TPA-TCNE and Fl-TPA-TCNQ (i.e., to produce red shifts in their absorption spectra and significant reductions in their band gaps). These changes are reflected in the electrical digital memory behavior of the polymers. Moreover, the TCNE and TCNQ units were found to diversify the digital memory modes and to widen the active polymer layer thickness window. In devices with aluminum top and bottom electrodes, the Fl-TPA polymer exhibits stable unipolar permanent memory behavior with high reliability. The Fl-TPA-TCNE and Fl-TPA-TCNQ devices exhibit stable unipolar permanent memory behavior as well as dynamic random access memory behavior with excellent reliability. These polymer devices were found to operate by either hole injection or hole injection along with electron injection, depending on the polymer composition. Overall, this study demonstrated that the incorporation of π-conjugated cyano moieties, which control both the π-conjugation length and electron-accepting power, is a sound approach for the design and synthesis of high-performance digital memory polymers. The TCNE and TCNQ polymers synthesized in this study are highly suitable active materials for the low-cost mass production of high-performance, polarity-free, programmable, volatile, and permanent memory devices that can be operated with very low power consumption, high ON/OFF current ratios, and high reliability.

Chiroptical Control in Helical Receptor–Anion Complexes

Dimers of appropriately arranged anion-responsive π-conjugated moieties form helical structures by interaction with chiral anions. Terphenyl-bridged dimers of dipyrrolyldiketone boron complexes show chirality induced by binding l-amino acid anions, as observed by circular dichroism (CD) and circularly polarized luminescence (CPL). The preferred configurations of helical structures depend on the geometries of the terphenyl spacer moieties.

Donor-π-Acceptor Type Diphenylaminothiophenyl Anthracene-mediated Organic Photosensitizers for Dye-sensitized Solar Cells

Two new metal-free organic dyes bridged by anthracene-mediated π-conjugated moieties were successfully synthesized for use in a dye-sensitized solar cell (DSSC). A N,N-diphenylthiophen-2-amine unit in these dyes acts as an electron donor, while a (E)-2-cyano-3-(thiophen-2-yl)acrylic acid group acts as an electron acceptor and an anchoring group to the TiO2 electrode. The photovoltaic properties of (E)-2-cyano-3-(5-((10-(5(diphenylamino)thiophen-2-yl)anthracen-9-yl)ethynyl)thiophen-2-yl)acrylic acid (DPATAT) and (E)-2cyano-3-(5'-((10-(5-(diphenylamino)thiophen-2-yl)anthracen-9-yl)ethynyl)-2,2'-bithiophen-5-yl)acrylic acid (DPATABT) were investigated to identify the effect of conjugation length between electron donor and acceptor on the DSSC performance. By introducing an anthracene moiety into the dye structure, together with a triple bond and thiophene moieties for fine-tuning of molecular configurations and for broadening the absorption spectra, the short-circuit photocurrent densities (Jsc), and open-circuit photovoltages (Voc) of DSSCs were improved. The improvement of Jsc in DSSC made of DPATABT might be attributed to much broader absorption spectrum and higher molecular extinction coefficient (e) in the visible wavelength range. The DPATABT-based DSSC showed the highest power conversion efficiency (PCE) of 3.34% (ηmax = 3.70%) under AM 1.5 illumination (100 mW cm �2 ) in a photoactive area of 0.41 cm 2 , with the Jsc of 7.89 mA cm �2 , the Voc of 0.59 V, and the fill factor (FF) of 72%. In brief, the solar cell performance with DPATABT was found to be better than that of DPATAT-based DSSC.

Guided supramolecular polymerization of oligo(p-phenylenevinylene) functionalized bismelamines

Bismelamines end-functionalized with oligo(p-phenylenevinylene) self-aggregate in nonpolar solvent to form short nanorods by helical π-π stacking. This inherent self-aggregation can be guided to a supramolecular polymerization pathway by complexing with a cyanurate, leading to gel-forming elongated nanotapes lacking the helical sense of the π-conjugated moieties.

The influence of π-conjugated moieties on the thermodynamics of cooperatively self-assembling tricarboxamides

A detailed investigation of the self-assembly behaviour of C3-symmetrical tricarboxamides reveals that a larger π-conjugated core does not increase the stability of assemblies in an apolar solvent but makes the system more sensitive to destabilization by addition of a good solvent.

Perylene ligand wrapping G-quadruplex DNA for label-free fluorescence potassium recognition

A perylene ligand, N,N-bis-(1-aminopropyl-3-propylimidazol salt)-3,4,9,10-perylene tetracarboxylic acid diimide ligand (PDI), which consisted of π-conjugated perylene moiety and hydrophilic side chains with positively charged imidazole rings, was used to wrap G-quadruplex for fluorescence turn-on K+ recognition. Electrostatic attraction between PDI's positively charged imidazole rings and DNA's negatively charged phosphate backbones enabled PDI to accumulate on DNA. Upon trapping K+, these G-rich DNA sequences transitioned to G-quadruplex. Subsequently, PDI ligands wrapped G-quadruplex, in which the flat aromatic core of PDI ligand interacted with G-quartet through π–π stacking and the side chains were positioned in grooves through electrostatic interactions. Consequently, the interaction mode change and conformational transition from PDI stacked G-sequence to PDI wrapped G-quadruplex led to PDI fluorescence enhancement, which was readily monitored as the detection signal. This strategy excluded the sequence tagging step and exhibited high selectivity and sensitivity towards K+ ion with the linear detection range of 10–150nM. Besides, PDI ligands may hold diagnostic and therapeutic application potentials to human telomere and cancer cells.

Synthesis and Photodynamics of Fluorescent Blue BODIPY-Porphyrin Tweezers Linked by Triazole Rings

Novel zinc porphyrin tweezers in which two zinc porphyrins were connected with π-conjugated boron dipyrromethenes (BDP meso-Por(2) and BDP β-Por(2)) through triazole rings were synthesized to investigate the photoinduced energy transfer and electron transfer. The UV-vis spectrum of BDP β-Por(2) which has less bulky substituents than BDP meso-Por(2) exhibits splitting of the Soret band as a result of the interaction between porphyrins of BDP β-Por(2) in the excited state. Such interaction between porphyrins of both BDP β-Por(2) and BDP meso-Por(2) is dominant at room temperature, while the coordination of the nitrogen atoms of the triazole rings to the zinc ions of the porphyrins occurs at low temperature. The conformational change of the BDP-porphyrin composites was confirmed by the changes in UV-vis and fluorescence spectra depending on temperature. Photodynamics of BDP meso-Por(2) and BDP β-Por(2) has also been investigated by laser flash photolysis. Efficient singlet-singlet energy transfer from the ZnP to the π-conjugated BDP moiety of both BDP meso-Por(2) and BDP β-Por(2) occurred in opposite direction as compared to energy transfer from conventional BDP to ZnP due to the π-conjugation in nonpolar toluene. In polar benzonitrile, however, additional electron transfer occurred along with energy transfer.

Preparation and characterization of high performance Schiff-base liquid crystal diepoxide polymer

A novel Schiff-base liquid crystal diepoxide polymer was prepared via a thermal copolymerization of a Schiff-base epoxy monomer (PBMBA) with a diamine co-monomer (MDA). We first proposed that specific effects of highly conjugated Schiff-base moiety on thermal properties of the Schiff-base epoxy polymer (PBMBA/MDA). Thermal degradation behavior of the polymer was characterized using thermogravimetric analysis (TGA) under nitrogen and under air, respectively. Thermogravimetric data obtained from TGA under nitrogen and under air reveal that PBMBA/MDA exhibits higher thermal stability compared with bisphenol-A type epoxy polymer (DGEBA/MDA) and other mesogene-containing epoxy polymer. It is worth pointing out that the outstanding residual char value for the Schiff-base epoxy polymers had been rarely reported. For thermal degradation mechanism of PBMBA/MDA under nitrogen, thermogravimetric analysis/infrared spectrometry (TG-IR) were used to investigate volatile components, and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) was used to explore morphologies and chemical components of the residual char. The effects of calcination temperature and calcination time on evolution of morphologies and chemical components of the residual char have been studied. It is proposed that the highly π-conjugated Schiff-base moiety is not only involved in a formation of intramolecular hydrogen bonding increasing the onset thermal degradation temperature (Td), but also possesses an effective charring ability retarding a further degradation of polymers. Due to the presence of the specific effects, the thermal stability of the Schiff-base epoxy is improved.

New strapped porphyrins as hosts for fullerenes: synthesis and complexation study

New strapped porphyrin-based hosts with different π-conjugated moieties and linkers have been prepared and their ability to bind with fullerenes was studied in dilute solution. We found that the ability of these hosts to bind with fullerenes strongly depends on their chemical nature and more precisely on the substitution pattern of the porphyrin deck. As expected, the more electron-rich hosts containing either an exTTF or a porphyrin unit as the strap bind fullerenes more efficiently with association constants of up to 3.9 × 10(5) M(-1). The results clearly demonstrate the potential of such hosts as a supramolecular scaffold for surface immobilization of pristine fullerenes.