Negatively Curved Octagon-Incorporated Aza-nanographene and its Assembly with Fullerenes.

A negatively curved aza-nanographene (NG) containing two octagons was synthesized by a regioselective and stepwise cyclodehydrogenation procedure, in which a double aza[7]helicene was simultaneously formed as an intermediate. Their saddle-shaped structures with negative curvature were unambiguously confirmed by X-ray crystallography, thereby enabling the exploration of the structure-property relationship by photophysical, electrochemical and conformational studies. Moreover, the assembly of the octagon-embedded aza-NG with fullerenes was probed by fluorescence spectral titration, with record-high binding constants (Ka=9.5×103 M-1 with C60, Ka=3.7×104 M-1 with C70) found among reported negatively curved polycyclic aromatic compounds. The tight association of aza-NG with C60 was further elucidated by X-ray diffraction analysis of their co-crystal, which showed the formation of a 1 : 1 complex with substantial concave-convex interactions.

The Synthesis of a Multiple D-A Conjugated Macrocycle and Its Application in Organic Photovoltaic.

As a novel class of materials, D-A conjugated macrocycles hold significant promise for chemical science. However, their potential in photovoltaic remains largely untapped due to the complexity of introducing multiple donor and acceptor moieties into the design and synthesis of cyclic π-conjugated molecules. Here, we report a multiple D-A ring-like conjugated molecule (RCM) via the coupling of dimer molecule DBTP-C3 as a template and thiophenes in high yields. RCM exhibits a narrow optical gap (1.33 eV) and excellent thermal stability, and shows a remarkable photoluminescence yield (ΦPL ) of 11.1 % in solution, much higher than non-cyclic analogues. Organic solar cell (OSC) constructed with RCM as electron acceptor shows efficient charge separation at donor-acceptor band offsets and achieves a power conversion efficiency (PCE) of 14.2 %-approximately fourfold higher than macrocycle-based OSCs reported so far. This is partly due to low non-radiative voltage loss down to 0.20 eV and a high electroluminescence yield (ΦEL ) of 4×10-4 . Our findings emphasize the potential of D-A cyclic conjugated molecules in advancing organic photovoltaic technology.

Photoresponse of Solution-Synthesized Graphene Nanoribbon Heterojunctions on Diamond Indicating Phototunable Photodiode Polarity.

Graphene nanoribbon heterostructures and heterojunctions have attracted interest as next-generation molecular diodes with atomic precision. Their mass production via solution methods and prototypical device integration remains to be explored. Here, the bottom-up solution synthesis and characterization of liquid-phase-processable graphene nanoribbon heterostructures (GNRHs) are demonstrated. Joint photoresponsivity measurements and simulations provide evidence of the structurally defined heterostructure motif acting as a type-I heterojunction. Real-time, time-dependent density functional tight-binding simulations further reveal that the photocurrent polarity can be tuned at different excitation wavelengths. Our results introduce liquid-phase-processable, self-assembled heterojunctions for the development of nanoscale diode circuitry and adaptive hardware.

Synthesis of a π-Extended Double [9]Helicene.

Double helicenes are appealing chiral frameworks. Their π-extension is desirable to achieve (chir)optical response in the visible and near-infrared (NIR) region, but access to higher double [n]helicenes (n≥8) has remained challenging. Herein, we report an unprecedented π-extended double [9]helicene (D9H), unambiguously revealing its structure by single-crystal X-ray diffraction. D9H shows remarkable NIR emission from 750 to 1100 nm with a high photoluminescence quantum yield of 18 %. In addition, optically pure D9H exhibits panchromatic circular dichroism with a notable dissymmetry factor (gCD ) of 0.019 at 590 nm, which is among the highest in the visible region for reported helicenes.

Solution-Synthesized Extended Graphene Nanoribbons Deposited by High-Vacuum Electrospray Deposition.

Solution-synthesized graphene nanoribbons (GNRs) facilitate various interesting structures and functionalities, like nonplanarity and thermolabile functional groups, that are not or not easily accessible by on-surface synthesis. Here, we show the successful high-vacuum electrospray deposition (HVESD) of well-elongated solution-synthesized GNRs on surfaces maintained in ultrahigh vacuum. We compare three distinct GNRs, a twisted nonplanar fjord-edged GNR, a methoxy-functionalized "cove"-type (or also called gulf) GNR, and a longer "cove"-type GNR both equipped with alkyl chains on Au(111). Nc-AFM measurements at room temperature with submolecular imaging combined with Raman spectroscopy allow us to characterize individual GNRs and confirm their chemical integrity. The fjord-GNR and methoxy-GNR are additionally deposited on nonmetallic HOPG and SiO2, and fjord-GNR is deposited on a KBr(001) surface, facilitating the study of GNRs on substrates, as of now not accessible by on-surface synthesis.

A C3-symmetric triple oxa[6]helicene with circularly polarized luminescence featuring parallel transition dipole moments.

We present the synthesis and characterization of the first triple oxa[6]helicene with C3 symmetry. In contrast to the reported D3-symmetric triple oxa[7]helicene, the C3-symmetric analogue holds parallel electric and magnetic transition dipole moments and thus enhanced luminescence dissymmetry, shedding light on the critical role of molecular symmetry on chiroptical response.

Controlling the Emissive, Chiroptical, and Electrochemical Properties of Double [7] Helicenes through Embedded Aromatic Rings.

We present here the synthesis and in-depth physicochemical characterization of a double hetero[7]helicene fused with four triazole rings at both helical ends. The comparison of this triazole-fused double helicene with the previously reported all-carbon and thiadiazole-fused analogs revealed the huge impact of the embedded aromatic rings on the photophysical features. The small structural variation of the terminal rings from thiadiazole to triazole caused a dramatic change of the photoluminescence quantum yields (PLQYs) from <1 % to 96 %, while the replacement of the terminal benzene rings with triazole rings induced a tenfold enhancement of the circularly polarized luminescence dissymmetry factor. These observations were well corroborated with transient absorption analysis and/or theoretic calculations. In addition, the triazole-fused double helicene exhibited ambipolar redox behavior, enabling the generation of radical cation and anion species by electrochemical and chemical methods and showing its potential for spin-related applications.

Double Thia/sulfone[7]helicenes with Controlled Photophysical and Chiroptical Properties by Heteroatom Variation.

The development of helicenes with strong chiroptical response and controlled photophysics is highly desirable but challenging. In this work, double thia/sulfone[7]helicenes were synthesized to investigate the heteroatom effect on the photophysical and chiroptical properties of double heterohelicenes through comparison with the previously reported double oxa[7]helicene. By variation of the embedded heteroatoms from oxygen to sulfur, the absorption and emission were significantly red-shifted, along with the improved luminescence dissymmetry factor (glum ). In particular, the double sulfone[7]helicene exhibited strong red to near-infrared (NIR) emission with glum of 1.1×10-3 , suggesting its potential as a NIR circularly polarized luminescence emitter.

Electron-Deficient Contorted Polycyclic Aromatic Hydrocarbon via One-Pot Annulative π-Extension of Perylene Diimide.

The synthesis of a class of contorted electron-deficient polycyclic aromatic hydrocarbons (PAHs) has been achieved by a one-pot bay annulation of perylene diimide involving a mild Suzuki coupling and subsequent air-mediated, ambient-light-induced photocyclization. X-ray crystallography unambiguously confirmed the contorted PAH structure bearing four imide groups. The photophysical and electronic properties of these contorted PAHs were also analyzed, showing a high fluorescence quantum yield of 86% and moderate electron mobility of 0.017 cm2 V-1 s-1.

Self-assembly and photoinduced fabrication of conductive nanographene wires on boron nitride.

Manufacturing molecule-based functional elements directly at device interfaces is a frontier in bottom-up materials engineering. A longstanding challenge in the field is the covalent stabilization of pre-assembled molecular architectures to afford nanodevice components. Here, we employ the controlled supramolecular self-assembly of anthracene derivatives on a hexagonal boron nitride sheet, to generate nanographene wires through photo-crosslinking and thermal annealing. Specifically, we demonstrate µm-long nanowires with an average width of 200 nm, electrical conductivities of 106 S m-1 and breakdown current densities of 1011 A m-2. Joint experiments and simulations reveal that hierarchical self-assembly promotes their formation and functional properties. Our approach demonstrates the feasibility of combined bottom-up supramolecular templating and top-down manufacturing protocols for graphene nanomaterials and interconnects, towards integrated carbon nanodevices.

Water-Soluble Nanoparticles with Twisted Double [7]Carbohelicene for Lysosome-Targeted Cancer Photodynamic Therapy.

Helicene-based therapeutic agents for organelle-targeted photodynamic therapy (PDT) involving both type I and II are challenging and still underexplored. Herein, water-soluble nanoparticles containing twisted double [7]carbohelicene (D7H-NPs) are prepared through self-assembly with 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] by a nanoprecipitation method. D7H-NPs display high water solubility with an average size of 46 ± 2 nm. Notably, D7H-NPs can generate efficient singlet oxygen (1 O2 ) and superoxide anion (O2· - ) upon white light irradiation, forming the basis of PDT. Moreover, the typical accumulation in lysosomes of 4T1 cancer cells paves the way to use D7H-NPs for lysosome-targeted cancer phototherapeutics. This paper reports a promising helicene-based phototherapeutic agent involving both type I and II PDT for organelle-targeted biotherapy.

X-shaped thiadiazole-containing double [7]heterohelicene with strong chiroptical response and π-stacked homochiral assembly.

An X-shaped double [7]heterohelicene 1 bearing four thiadiazole units is synthesized by regioselective cyclodehydrogenation. Enantiopure 1 exhibits excellent chiroptical properties with an impressive absorption dissymmetry factor of up to 0.027, as well as a compact π-stacked homochiral assembly which is unprecedented in the realm of double helicenes.

S-Shaped Double Helicene Diimides: Synthesis, Self-Assembly, and Mechanofluorochromism.

Herein we present a synthesis of an S-shaped double helicene with fused imide moieties, achieving a contorted aromatic diimide (DHDI) with good fluorescence properties in both solution and the solid state. DHDI demonstrates distinct mechanofluorochromism from yellow to green emission under grinding of its crystalline powder.

Dicyclopentaannelated Hexa-peri-hexabenzocoronenes with a Singlet Biradical Ground State.

Synthesis of two dicyclopentaannelated hexa-peri-hexabenzocoronene (PHBC) regioisomers was carried out, using nonplanar oligoaryl precursors with fluorenyl groups: mPHBC 8 with two pentagons in the "meta"-configuration was obtained as a stable molecule, while its structural isomer with the "para"-configuration, pPHBC 16, could be generated and characterized only in situ due to its high chemical reactivity. Both PHBCs exhibit low energy gaps, as reflected by UV-vis-NIR absorption and electrochemical measurements. They also show open-shell singlet ground states according to electron paramagnetic resonance (EPR) measurements and density functional theory (DFT) calculations. The use of fully benzenoid HBC as a bridging moiety leads to significant singlet biradical characters (y0 ) of 0.72 and 0.96 for mPHBC 8 and pPHBC 16, respectively, due to the strong rearomatization tendency of the HBC π-system; these values are among the highest for planar carbon-centered biradical molecules. The incorporation of fully unsaturated pentagons strongly perturbs the aromaticity of the parent HBC and makes the constituted benzene rings less aromatic or antiaromatic. These results illustrate the high impact of cyclopentaannelation on the electronic structures of fully benzenoid polycyclic aromatic hydrocarbons (PAHs) and open up a new avenue towards open-shell PAHs with prominent singlet biradical characters.

Amplification of Dissymmetry Factors in π-Extended [7]- and [9]Helicenes.

π-Extended helicenes constitute an important class of polycyclic aromatic hydrocarbons with intrinsic chirality. Herein, we report the syntheses of π-extended [7]helicene 4 and π-extended [9]helicene 6 through regioselective cyclodehydrogenation in high yields, where a "prefusion" strategy plays a key role in preventing undesirable aryl rearrangements. The unique helical structures are unambiguously confirmed by X-ray crystal structure analysis. Compared to the parent pristine [7]helicene and [9]helicene, these novel π-extended helicenes display significantly improved photophysical properties, with a quantum yield of 0.41 for 6. After optical resolution by chiral high-performance liquid chromatography, the chiroptical properties of enantiomers 4-P/M and 6-P/M are investigated, revealing that the small variation in helical length from [7] to [9] can cause an approximately 10-fold increase in the dissymmetry factors. The circularly polarized luminescence brightness of 6 reaches 12.6 M-1 cm-1 as one of the highest among carbohelicenes.

Furan-containing double tetraoxa[7]helicene and its radical cation.

An unprecedented furan-based double oxa[7]helicene 1 was achieved, featuring a stable twisted conformation with π-overlap at both helical ends. The excellent conformational stability allowed for optical resolution of 1, which provided a pair of enantiomers exhibiting pronounced mirror-imaged circular dichroism and circularly polarized luminescence activity. The radical cation of 1 was obtained by chemical oxidation as evidenced by UV-Vis-NIR absorption, electron paramagnetic resonance spectroscopy and in situ spectroelectrochemistry. The present work is the starting point for the investigation of open-shell oxahelicenes.

Negatively Curved Nanographene with Heptagonal and [5]Helicene Units.

Negatively curved nanographene (NG) 4, having two heptagons and a [5]helicene, was unexpectedly obtained by aryl rearrangement and stepwise cyclodehydrogenations. X-ray crystallography confirmed the saddle-shaped structures of intermediate 3 and NG 4. The favorability of rearrangement over helicene formation following radical cation or arenium cation mechanisms is supported by theoretical calculations. NG 4 demonstrates a reversible mechanochromic color change and solid-state emission, presumably benefiting from its loose crystal packing. After resolution by chiral high-performance liquid chromatography, the circular dichroism spectra of enantiomers 4-(P) and 4-(M) were measured and showed moderate Cotton effects at 350 nm (|Δε| = 148 M-1 cm-1).

Compressing Double [7]Helicene by Successive Charging with Electrons.

Chemical reduction of a benzo-fused double [7]helicene (1) with two alkali metals, K and Rb, provided access to three different reduced states of 1. The doubly-reduced helicene 12- has been characterized by single-crystal X-ray diffraction as a solvent-separated ion triplet with two potassium counterions. The triply- and tetra-reduced helicenes, 13- and 14- , have been crystallized together in an equimolar ratio and both form the contact-ion complexes with two Rb+ ions each, leaving three remaining Rb+ ions wrapped by crown ether and THF molecules. As structural consequence of the stepwise reduction of 1, the central axis of helicene becomes more compressed upon electron addition (1.42 Šin 14- vs. 2.09 Šin 1). This is accompanied by an extra core twist, as the peripheral dihedral angle increases from 16.5° in 1 to 20.7° in 14- . Theoretical calculations provided the pattern of negative charge build-up and distribution over the contorted helicene framework upon each electron addition, and the results are consistent with the X-ray crystallographic and NMR spectroscopic data.

Correction: A new non-fullerene acceptor based on the combination of a heptacyclic benzothiadiazole unit and a thiophene-fused end group achieving over 13% efficiency.

Correction for 'A new non-fullerene acceptor based on the combination of a heptacyclic benzothiadiazole unit and a thiophene-fused end group achieving over 13% efficiency' by Yunqiang Zhang et al., Phys. Chem. Chem. Phys., 2019, DOI: .

A new non-fullerene acceptor based on the combination of a heptacyclic benzothiadiazole unit and a thiophene-fused end group achieving over 13% efficiency.

A new non-fullerene acceptor, namely Y10, based on dithienothiophen[3,2-b]-pyrrolobenzothiadiazole (TPBT) as the central core and 2-(6-oxo-5,6-dihydro-4H-cyclopenta[c]thiophen-4-ylidene)malononitrile (TC) as the electron-deficient end group, has been designed and synthesized. Y10 reveals a narrow optical energy gap (Eoptg) of 1.35 eV with a broad absorption band from 600 to 900 nm. A wide bandgap polymer, J11, as the donor material (Eoptg = 1.96 eV) is used to blend with Y10 for the construction of organic solar cell devices, which achieve an impressive power conversion efficiency (PCE) of 13.46% with an open circuit voltage (Voc) of 0.89 V, a short circuit current (Jsc) of 21.21 mA cm-2, and a fill factor (FF) of 71.55%, with thermal annealing treatment at 100 °C for 5 min and 0.8 wt% 1-chloronaphthalene (CN) as an additive. These results indicate that the incorporation of the TPBT unit as the central core and the TC unit as the electron-deficient end group provides an efficient strategy for the construction of high performance solar cells.