Π-conjugated Skeleton Research Articles

Perylene-Fused, Aggregation-Free Polycyclic Aromatic Hydrocarbons for Solution-Processed Distributed Feedback Lasers.

Perylene-fused, aggregation-free polycyclic aromatic hydrocarbons with partial zigzag periphery (ZY-01, ZY-02, and ZY-03) were synthesized. X-ray crystallographic analysis reveals that there is no intermolecular π-π stacking in any of the three molecules, and as a result, they show moderate-to-high photoluminescence quantum yield in both solution and in the solid state. They also display the characteristic absorption and emission spectra of perylene dyes. ZY-01 and ZY-02 with a nearly planar π-conjugated skeleton exhibit amplified spontaneous emission (ASE) when dispersed in polystyrene thin films. Solution-processed distributed feedback lasers have been fabricated using ZY-01 and ZY-02 as active gain materials, both showing narrow emission linewidth (<0.4 nm) at wavelengths around 515 and 570 nm, respectively. In contrast, ZY-03 did not show ASE and lasing, presumably due to its highly twisted backbone, which facilitates nonradiative internal conversion and intersystem crossing.

Design, synthesis, and characterization of a new class of efficient dihydropyridazine-dibenzosuberenone derived fluorescent dyes and investigation of their some photophysical properties

A new series of dihydropyridazine-dibenzosuberenone derivatives has been efficiently prepared by inverse Diels-Alder cycloaddition reactions between tetrazines and dibenzosuberenone derivatives bearing various electron-withdrawing and electron-donating substituents. In total, 14 new fluorescent dyes were designed, synthesized, and characterized. The influence of substituents placed at the 3- and 7-positions of the dibenzosuberenone ring on photophysical properties of the compounds has been investigated in toluene. The photophysical properties of the synthesized compounds were investigated by comparing both with each other and with the unsubstituted derivate which synthesized previously via our research group. Compared with their unsubstituted analogues, the 3,7-substituted dihydropyridazine-dibenzosuberenone derivatives showed red shifts of absorption and emission maxima, which might be attributed to the large π-conjugated skeleton that was beneficial to electron delocalization. Moreover, a very high fluorescence quantum yields (up to 0.99) and large Stokes shifts (up to 130 nm) of the dibenzosuberenone derivatives were also found, which could make them be found wide potential applications in different fields such as fluorescence sensors, biological image, and optoelectronic materials.

S⋯Cl intramolecular interaction: An efficient strategy to improve power conversion efficiency of organic solar cells

Noncovalent conformational locks (NCLs) including S⋯N, Se⋯O, and S⋯O etc. Have been an effective strategy to improve the planarity and rigidity, and charge transport mobility of organic/polymeric semiconductors. Herein, by replacing methyl group (ITMIC) with chlorine (ITCIC) in the π-bridge, the planarity and rigidity of the π-conjugated skeleton was enhanced by introduction of S⋯Cl NCLs, thus the charge transport mobility was improved accordingly. As a result, PM6:ITCIC based organic solar cells showed impressive PCE of 11.34%, much higher than that based on PM6:ITMIC. This contribution demonstrated a novel kind NCLs (S⋯Cl) for improving the performance of organic solar cells.

Imine-Rich Poly( o -phenylenediamine) as High-Capacity Trifunctional Organic Electrode for Alkali-Ion Batteries

Alkali-ion batteries, including potassium-ion batteries, lithium-ion batteries, and sodium-ion batteries are important energy storage devices; however, with the cation size increased, there exists ...

Wave-shaped polycyclic hydrocarbons with controlled aromaticity.

Controlling the aromaticity and electronic properties of curved π-conjugated systems has been increasingly attractive for the development of novel functional materials for organic electronics. Herein, we demonstrate an efficient synthesis of two novel wave-shaped polycyclic hydrocarbons (PHs) 1 and 2 with 64 π-electrons. Among them, the wave-shaped π-conjugated carbon skeleton of 2 is unambiguously revealed by single-crystal X-ray crystallography analysis. The wave-shaped geometry is induced by steric congestion in the cove and fjord regions. Remarkably, the aromaticity of these two structural isomers can be tailored by the annulated direction of cyclopenta[b]fluorene units. Isomer 1 (Eoptg = 1.13 eV) behaves as a closed-shell compound with weakly antiaromatic feature, whereas its structural isomer 2 displays a highly stable tetraradical character (y 0 = 0.23; y 1 = 0.22; t 1/2 = 91 days) with a narrow optical energy gap of 0.96 eV. Moreover, the curved PH 2 exhibits remarkable ambipolar charge transport in solution-processed organic thin-film transistors. Our research provides a new insight into the design and synthesis of stable functional curved aromatics with multiradical characters.

Crystal Structures of Two Perylenediimides: A Study of Bay-Substitution

The crystal structures of N,N′-bis(2,6-diisopropylphenyl)-3,4,9,10-perylenetetracarboxylic diimide (PDI-1) and 1,6,7,12-tetrakis(4-tert-butylphenoxy)-N,N′-bis(2,6-diisopropylphenyl)-3,4,9,10-perylenetetracarboxylic diimide (PDI-2) are reported for the first time. The π-conjugated perylene skeleton of PDI-1 is nearly planar while the tetra tert-butylphenoxy substitution on bay positions give rise to highly twisted perylene skeleton in PDI-2. Density functional theory and the Boltzmann transport equation has been applied to calculate the semiclassical thermoelectric transport properties of crystalline PDI-1 and PDI-2 as a function of solid-state packing, and the effect of bay-substitution have been investigated.

Photophysical insights on the influence of excited states reorganization processes on the visible and near infra-red luminescence of two-photon quadrupolar chromophores

We synthesized three different families of quadrupolar dyes, differing by the nature of their aromatic central cores (phenyl, fluorenyl, anthracenyl), in which we systematically varied the length of the π-conjugated backbone and the nature of the central bridge. We compared their linear and non-linear spectroscopic and photophysical features. We showed that the introduction of a diyne bridge is efficient in consistently increasing the Stokes shifts in these fluorophores, especially in high polarity solvents. By a combined theoretical and spectroscopic study we show that this feature is favoured by distortion of their π-conjugated skeleton at the electronic ground state. Unfortunately, this distortion process is generally detrimental to their fluorescence quantum yields. However, in the course of this study, we identify a particularly promising dye, that combines a large two-photon absorption (650 GM@760 nm) while keeping efficient emission (ϕf = 0.3) in the far-red/NIR (ca 700 nm) in polar solvent (DMSO).

Engineering Rotaxane-Based Nanoarchitectures via Topochemical Photo-Cross-Linking

Polymerization of monomers included by macrocyclic hosts has been found as an efficient way to synthesize sophisticated rotaxane-based nanostructures, whereas such a process triggered by photon has received little coverage so far. Herein, a new diphenyldiacetylene (DPDA) derivative (compound 1) comprising viologen as a binding site toward cucurbit[7]uril (CB[7]) macroring, and isophthalate as a bulky stopper, was rationally designed and prepared. After verifying the photo-cross-linking efficiency of compound 1 upon its regular self-assembly, we also achieved a straightforward construction of rotaxane-based nanoarchitecture 2 ⊂ CB[7] through an in situ photoirradiation on the corresponding pseudo[2]rotaxane 1 ⊂ CB[7]. Although the threading of CB[7] changed the self-assembly behavior of the DPDA derivative, the topochemical reaction could be definitely observed to afford the corresponding photo-cross-linked species. Such a process could be facilely indicated by distinctive photoluminescence enhancement on the basis of π-conjugated skeleton change of DPDA toward potential usage of rotaxane-based systems as smart optoelectronic materials. We anticipate this unique strategy will allow new visions for the synthesis and application of novel luminescent host–guest nanoarchitectures.

Synthesis and properties of [7]helicene and [7]helicene-like compounds with a cyclopenta[1,2-b:4,3-b']dithiophene or dithieno[2,3-b:3',2'-d]heterole skeleton.

A series of [7]helicene and [7]helicene-like compounds composed of a cyclopenta[1,2-b:4,3-b']dithiophene or dithieno[2,3-b:3',2'-d]heterole moiety and two naphthalene moieties were successfully synthesized from a common synthetic intermediate, 1,1'-binaphtho[2,1-b]thiophene. Their helical structures were confirmed by X-ray crystallographic analysis. The photophysical properties of them and their benzene analogues were investigated via absorption and fluorescence spectroscopy and theoretical calculations to correlate the effect of the five-membered rings in their π-conjugated skeleton. Through these investigations, the photophysical properties were found to largely depend on a combination of the central five-membered ring and the neighboring two aromatic rings. In particular, a combination of the central five-membered ring with electron-withdrawing character and the two neighboring thiophene rings was revealed to induce red-shifted emission.

Luminescent non-traditional π-gels fabricated from pyrimidine derivatives bearing carbazole for the detection of acid vapors

A series of new pyrimidine derivatives modified with carbazole (CM, CMH, CMCl and CMBr) and tert-butyl carbazole (TCM, TCMH, TCMCl and TCMBr) were synthesized. It was found that CM, CMCl, CMBr, TCM, TCMCl and TCMBr without traditional gelation groups could self-assemble into organogels with intense emission. It was found that V-shaped π-conjugated skeleton and π-π interactions were essential for the organogelation. It was interesting that the organogels could be destroyed by adding TFA (trifluoroacetic acid), accompanied with the quenching of the emission on account of the protonation of pyrimidine unit. In particular, the xerogel-based film of TCM emitting strong bluish green light could be used as fluorescent sensor to detect TFA vapor with the decay time and detection limit of 0.6 s and 95 ppb, respectively. Such high performance of the xerogel-based film in fluorescent responsive ability was originated from the high surface-to-volume ratios of nanomaterials and the large space in 3D networks, which were favorable for the adsorption and diffusion of the analytes. We provided new strategy for the design of non-traditional π-gelators and the fabrication of fluorescent sensory materials with high performance to detect gaseous analytes.

How Large Can We Build a Cyclic Assembly? Impact of Ring Size on Chelate Cooperativity in Noncovalent Macrocyclizations.

Self-assembled systems rely on intramolecular cooperative effects to control their growth and regulate their shape, thus yielding discrete, well-defined structures. However, as the size of the system increases, cooperative effects tend to dissipate. We analyze here this situation by studying a set of oligomers of different lengths capped with guanosine and cytidine nucleosides, which associate in cyclic tetramers by complementary Watson-Crick H-bonding interactions. As the monomer length increases, and thus the number of C(sp)-C(sp2 ) σ-bonds in the π-conjugated skeleton, the macrocycle stability decreases due to a notable reduction in effective molarity (EM), which has a clear entropic origin. We determined the relationship between EM or ΔS and the number of σ-bonds, which allowed us to predict the maximum monomer lengths at which cyclic species would still assemble quantitatively, or whether the cyclic species would not able to compete at all with linear oligomers over the whole concentration range.

5]Helicene derivatives containing aromatic imide moiety: Synthesis, structure, and photophysical properties

A series of diaryl-substituted [5]helicene derivatives containing aromatic imide moiety were effectively synthesized. From the single crystal of 3, obviously helical structure with a torsion angle of 65.4° was detected. Compared with their tetrahydro[5]helicene analogues, the [5]helicene derivatives showed longer absorption wavelength and larger molar absorptivity, which might be attributed to the large π-conjugated skeleton that was beneficial to electron delocalization at ground state. Moreover, except for 5k, long emission wavelength (520–545nm), medium fluorescence quantum yields (14.4–21.6%) and large Stokes shifts (89–95nm) of the [5]helicene derivatives were also found, which could make them be found wide potential applications in optoelectronic materials.

Synthesis of Chlorine-Substituted Graphdiyne and Applications for Lithium-Ion Storage.

Chlorine-substituted graphdiyne (Cl-GDY) is prepared through a Glaser-Hay coupling reaction on the copper foil. Cl-GDY is endowed with a unique π-conjugated carbon skeleton with expanded pore size in two dimensions, having graphdiyne-like sp- and sp2 - hybridized carbon atoms. As a result, the transfer tunnels for lithium (Li) ions in the perpendicular direction of the molecular plane are enlarged. Moreover, benefiting from the bottom-to-up fabrication procedure of graphdiyne and the strong chemical tailorability of the alkinyl-contained monomer, the amount of substitutional chlorine atoms with appropriate electronegativity and atom size is high and evenly distributed on the as-prepared carbon framework, which will synergistically stabilize the Li intercalated in the Cl-GDY framework, and thus generate more Li storage sites. Profiting from the above unique structure, Cl-GDY shows remarkable electrochemical properties in lithium ion half-cells.

Super-Photostable Phosphole-Based Dye for Multiple-Acquisition Stimulated Emission Depletion Imaging.

As stimulated emission depletion (STED) microscopy can provide structural details of cells with an optical resolution beyond the diffraction limit, it has become an indispensable tool in cell biology. However, the intense STED laser beam usually causes rapid photobleaching of the employed fluorescent dyes, which significantly limits the utility of STED microscopy from a practical perspective. Herein we report a new design of super-photostable dye, PhoxBright 430 (PB430), comprising a fully ring-fused π-conjugated skeleton with an electron-accepting phosphole P-oxide unit. We previously developed a super-photostable dye C-Naphox by combining the phosphole unit with an electron-donating triphenylamine moiety. In PB430, removal of the amino group alters the transition type from intramolecular charge transfer character to π-π* transition character, which gives rise to intense fluorescence insensitive to molecular environment in terms of fluorescence colors and intensity, and bright fluorescence even in aqueous media. PB430 also furnishes high solubility in water, and is capable of labeling proteins with maintaining high fluorescence quantum yields. This dye exhibits outstanding resistance to photoirradiation even under the STED conditions and allows continuous acquisition of STED images. Indeed, using a PB430-conjugated antibody, we succeed in attaining a 3-D reconstruction of super-resolution STED images as well as photostability-based multicolor STED imaging of fluorescently labeled cytoskeletal structures.

New non-traditional organogelator of β-diketone-boron difluoride complexes with terminal tetraphenylethene: Self-assembling and fluorescent sensory properties towards amines

New β-diketone-boron difluoride complexes functionalized with tetraphenylethene (TPEB, DTPEB and TTPEB) which exhibit AIE (aggregation-induced emission) properties have been synthesized. It was found that only boomerang-shaped DTPEB without any traditional gelation groups could form organogel in specific organic solvents. It gave strong orange red fluorescence in organogel as well as in xerogel-based film although it was non-emissive in solution. It is interesting that the emission of DTPEB in xerogel-based film could be quenched significantly upon exposure to triethylamine (TEA) vapour, and the detection limit was as low as ca. 0.1 ppb. This work provides a strategy for the synthesis of a new rigid non-traditional π-gelator via the construction of a boomerang-shaped π-conjugated skeleton. In addition, the gelation of the π-gelators with AIE ability is a facile method for the fabrication of luminescent organic nanomaterials.

π-Extended and Curved Antiaromatic Polycyclic Hydrocarbons.

Synthesis of antiaromatic polycyclic hydrocarbons (PHs) is challenging because the high energy of their highest occupied molecular orbital and low energy of their lowest unoccupied molecular orbital cause them to be reactive and unstable. In this work, two large antiaromatic acene analogues, namely, cyclopenta[pqr]indeno[2,1,7-ijk]tetraphene (CIT, 1a) and cyclopenta[pqr]indeno[7,1,2-cde]picene (CIP, 1b), as well as a curved antiaromatic molecule with 48 π-electrons, dibenzo[a,c]diindeno[7,1,2-fgh:7',1',2'-mno]phenanthro[9,10-k]tetraphene (DPT, 1c), are synthesized on the basis of the corona of indeno[1,2-b]fluorene. These three antiaromatic PHs possess a narrow energy gap down to 1.55 eV and exhibit high kinetic stability under ambient conditions. Moreover, these compounds display reversible electron transfer processes in both the cathodic and anodic regimes. Their cation and anion radicals are characterized by in situ vis-NIR absorption and electron paramagnetic resonance spectroelectrochemistry. The X-ray crystallographic analysis confirms that while CIP and CIT manifest planar structures, DPT shows a curved π-conjugated carbon skeleton. The synthetic strategy starting from ortho-substituted benzene units to construct five-membered rings in this work provides a unique entry to novel pentagon-embedding or curved antiaromatic polycyclic hydrocarbons. In addition, besides the detailed chemical and physical investigations, microscale single-crystal fiber field-effect transistors were also fabricated.

Self-aggregation of synthetic chlorophyll-c derivative and effect of C17-acrylate residue on bridging green gap in chlorosomal model

Abstract A zinc bacteriochlorophyll- d analog possessing a fully π-conjugated porphyrin skeleton and an acrylate residue at the 17-position was prepared by chemical modification of an accessory photosynthetic pigment, chlorophyll- c 1 from a diatom Chaetoceros species. The synthetic zinc chlorophyll- c 1 derivative self-aggregated in a less polar organic solvent and in a solid film to give a red-shifted and broadened visible absorption spectrum, which is similar to that of the main light-harvesting antenna of a green photosynthetic bacterium, where magnesium chlorins with the 17-propionate residue including bacteriochlorophyll- d aggregate in a J -type fashion to form large oligomers. The resulting self-aggregates showed specific and intense absorption bands at around 500 and 600 nm due to the π-extension along the molecular x-axis, which could bridge the “green gap” observed in the above natural antenna system. Visible and infrared absorption spectral analyses revealed that the supramolecular structure of self-aggregates of the zinc chlorophyll- c 1 derivative are comparable to those of the natural antenna, in spite of double dehydrogenation at the 17,18- and 17 1 ,17 2 -positions in the molecule.

A Stable Saddle-Shaped Polycyclic Hydrocarbon with an Open-Shell Singlet Ground State.

Diindeno-fused bischrysene, a new diindeno-based polycyclic hydrocarbon (PH), was synthesized and characterized. It was elucidated in detailed experimental and theoretical studies that this cyclopenta-fused PH possesses an open-shell singlet biradical structure in the ground state and exhibits high stability under ambient conditions (t1/2 =39 days). The crystal structure unambiguously shows a novel saddle-shaped π-conjugated carbon skeleton due to the steric hindrance of the central cove-edged bischrysene unit. UV/Vis spectral measurements revealed that the title molecule has a very narrow optical energy gap of 0.92 eV, which is consistent with the electrochemical analysis and further supported by density functional theory (DFT) calculations.

Highly-efficient polymer solar cells realized by tailoring conjugated skeleton of alcohol-soluble conjugated electrolytes

Compared with the popular conjugated polyelectrolytes as interfacial materials in polymer solar cells (PSCs), small molecule conjugated electrolytes (SMCEs) interlayers remains limited and the relationship between structures of small molecule electrolytes and device performance is still unclear. Herein, a series of alcohol-soluble small molecule conjugated electrolytes, combined with different conjugated skeletons and identical ammonium salt polar side chains, namely, 2T-(FN-Br)2, 3T-(FN-Br)2 and 4T-(FN-Br)2 were designed and synthesized as interfacial materials for the inverted polymer solar cells (I-PSCs), to explore the relevance between the π-conjugated skeleton and the device performance. As the conjugated bridge length and terminal group increased from 2T-(FN-Br)2, 3T-(FN-Br)2 to 4T-(FN-Br)2, the photovoltaic performances were gradually improved. The improved device performance caused by the enlarged π-conjugated skeleton mainly resulted from the optimized interfacial contact, effective modulation on the morphology of the active layer and the improvement of charge mobility. Encouragingly, devices with 4T-(FN-Br)2 as interfacial material achieved a high power conversion efficiency of 8.40%, based on thieno[3,4-b]-thiophene/benzodithiophene (PTB7): [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as light-harvesting layer. This work provided a new avenue to exploit novel promising interfacial modification materials by simply and slightly modulating the π-conjugated skeleton without complex molecular design.

Study on Synthesis and Fluorescence of Novel Benzofused Phenazine π-Conjugated Skeleton with Coumarin and Isophoron Cores.

The novel benzofused phenazine π-conjugated skeleton with a coumarin and isophoron core was synthesized, characterized, and condensed with suitably substituted active methylene compounds by classical Knoevenagel condensation reaction to obtain novel mono-styryl dyes 6a-6d. These novel styryl dyes have hue varying from yellow to violet. The geometries of the styryl dyes were optimized at B3LYP/6-31G (d) level of theory, and their electronic excitation properties were evaluated using density functional theory.