Stable π-Extended Thio[7]helicene-Based Diradical with Predominant Through-Space Spin-Spin Coupling.

In this work, a novel π-extended thio[7]helicene scaffold was synthesized, where the α-position of the thiophene unit could be functionalized with bulky phenoxy radicals after considerable synthetic attempts. This open-shell helical diradical, ET7H-R, possesses high stability in the air, nontrivial π conjugation, persistent chirality, and a high diradical character (y0 of 0.998). The key feature is a predominant through-space spin-spin coupling (TSC) between two radicals at the helical terminals. Variable-temperature continuous-wave electron spin resonance (cw-ESR) and superconducting quantum interference device (SQUID) magnetometry in the solid state reveal a singlet ground state with a nearly degenerate triplet state of ET7H-R. These results highlight the significance of a stable helical diradicaloid as a promising platform for investigating intramolecular TSCs.

Elimination of charge-carrier trapping by molecular design.

A common obstacle of many organic semiconductors is that they show highly unipolar charge transport. This unipolarity is caused by trapping of either electrons or holes by extrinsic impurities, such as water or oxygen. For devices that benefit from balanced transport, such as organic light-emitting diodes, organic solar cells and organic ambipolar transistors, the energy levels of the organic semiconductors are ideally situated within an energetic window with a width of 2.5 eV where charge trapping is strongly suppressed. However, for semiconductors with a band gap larger than this window, as used in blue-emitting organic light-emitting diodes, the removal or disabling of charge traps poses a longstanding challenge. Here we demonstrate a molecular strategy where the highest occupied molecular orbital and lowest unoccupied molecular orbital are spatially separated on different parts of the molecules. By tuning their stacking by modification of the chemical structure, the lowest unoccupied molecular orbitals can be spatially protected from impurities that cause electron trapping, increasing the electron current by orders of magnitude. In this way, the trap-free window can be substantially broadened, opening a path towards large band gap organic semiconductors with balanced and trap-free transport.

Peri-Alkylated Terrylenes and Ternaphthalenes Building-Blocks Towards Multi-Edge Nanographenes.

Since its first synthesis by Clar in 1948, terrylene - a fully connected ternaphthalene oligomer via naphthalene's peri-positions - has gained special focus within the rylene family, drawing interest for its unique chemical, structural, optoelectronic and single photon emission properties. In this study, we introduce a novel synthetic pathway that enhances the solubility of terrylene derivatives through complete peri-alkylation, while also facilitating extensions at the bay-positions. This approach not only broadens the scope of terrylene's chemical versatility but also opens new avenues for developing solution processable novel multi-edge nanographenes and tailoring electronic energy levels through topological edge structures. Our findings include a comprehensive structural and spectroscopic characterization along with transient absorption spectroscopy and photophysics of both the synthesized peri-alkylated terrylene and its phenylene-fused derivative.

Nonalternating π-System Mediated Spin Coupling in Azulene Nitronyl Nitroxide Diradicals.

To explore the distinctions in spin coupling between the molecular bridges of alternating and nonalternating π-systems, we synthesized a pair of isoelectronic compounds, namely, 2,6-Na-NN and 2,6-Az-NN, by utilizing naphthalene and azulene (naphthalene = Na and azulene = Az) as the bridges, respectively. Moreover, we conducted assessments to predict the coupling paths for nonalternating azulene. Variable-temperature EPR (VT-EPR) and SQUID results consistently reveal that both 2,6-Na-NN and 2,6-Az-NN exhibit antiferromagnetic coupling interactions, with coupling constants of J(2,6-Na-NN) = -22.3 cm-1 and J(2,6-Az-NN) = -30.1 cm-1, respectively. Density functional theory computations support these discoveries by revealing negative coupling constants (J < 0) and the spin densities population of the diradicals are observed to delocalize into the molecular bridges. This work suggests the most suitable coupling path for 2,6-Az-NN. In addition, we have investigated the potential spatial resistance of the diradicals in conjunction with single-crystal data. Theoretical calculations underestimating the torsion angle of the diradicals and overestimating the value of the magnetic coupling provide an explanation for this phenomenon. The final experimental results and theoretical calculations show that the 2,6-Az-NN coupling path prefers short paths.

TADF Blue Emitters with Balanced π-Conjugation─Design, Synthesis, Spectral Characterization, and a Model OLED with 8-(5-(tert-Butyl)-1,3,4-oxadiazol-2-yl)-N,N-bis(4-(tert-butyl)phenyl)dibenzo[b,d]furan-2-amine.

Blue organic light-emitting diodes (OLED) suffer from relatively short lifetimes and a comparatively low lighting efficiency. One of the approaches to improving their characteristics is the development of luminophores with the potential for thermally activated delayed fluorescence (TADF). Herein, a set of donor-spacer-acceptor compounds with potential for TADF are designed, synthesized, and computationally and spectroscopically characterized. The excited state dynamics of the most prospective dye is monitored by time-resolved fluorescence and transient absorption spectroscopy. The experimental data are obtained and processed by a newly developed method and supplemented by quantum chemical calculations. The comprehensive approach allowed rationalization of the complex cascade-type photophysical behavior. The most promising emitter is included in an OLED displaying a blue color with a maximum EQE of 4.9% and negligible efficiency roll-off at higher luminance.

Publisher Correction: Magnetic edge states and coherent manipulation of graphene nanoribbons.

In Fig. 1 of this Letter, there should have been two nitrogen (N) atoms at the 1,3-positions of all the blue chemical structures (next to the oxygen atoms), rather than one at the 2-position. The figure has been corrected online, and the original incorrect figure is shown as Supplementary Information to the accompanying Amendment.

Magnetic edge states and coherent manipulation of graphene nanoribbons.

Graphene, a single-layer network of carbon atoms, has outstanding electrical and mechanical properties 1 . Graphene ribbons with nanometre-scale widths2,3 (nanoribbons) should exhibit half-metallicity 4 and quantum confinement. Magnetic edges in graphene nanoribbons5,6 have been studied extensively from a theoretical standpoint because their coherent manipulation would be a milestone for spintronic 7 and quantum computing devices 8 . However, experimental investigations have been hampered because nanoribbon edges cannot be produced with atomic precision and the graphene terminations that have been proposed are chemically unstable 9 . Here we address both of these problems, by using molecular graphene nanoribbons functionalized with stable spin-bearing radical groups. We observe the predicted delocalized magnetic edge states and test theoretical models of the spin dynamics and spin-environment interactions. Comparison with a non-graphitized reference material enables us to clearly identify the characteristic behaviour of the radical-functionalized graphene nanoribbons. We quantify the parameters of spin-orbit coupling, define the interaction patterns and determine the spin decoherence channels. Even without any optimization, the spin coherence time is in the range of microseconds at room temperature, and we perform quantum inversion operations between edge and radical spins. Our approach provides a way of testing the theory of magnetism in graphene nanoribbons experimentally. The coherence times that we observe open up encouraging prospects for the use of magnetic nanoribbons in quantum spintronic devices.

A Terrylene-Anthraquinone Dyad as a Chromophore for Photothermal Therapy in the NIR-II Window.

A terrylenedicarboximide-anthraquinone dyad, FTQ, with absorption in the second near-infrared region (NIR-II) is obtained as a high-performance chromophore for photothermal therapy (PTT). The synthetic route proceeds by C-N coupling of amino-substituted terrylenedicarboximide (TMI) and 1,4-dichloroanthraquinone followed by alkaline-promoted dehydrocyclization. FTQ with extended π-conjugation exhibits an optical absorption band peaking at 1140 nm and extending into the 1500 nm range. Moreover, as determined by dielectric spectroscopy in dilute solutions, FTQ achieves an ultrastrong dipole moment of 14.4 ± 0.4 Debye due to intense intramolecular charge transfer. After encapsulation in a biodegradable polyethylene glycol (DSPE-mPEG2000), FTQ nanoparticles (NPs) deliver a high photothermal conversion efficiency of 49% under 1064 nm laser irradiation combined with excellent biocompatibility, photostability, and photoacoustic imaging capability. In vitro and in vivo studies reveal the great potential of FTQ NPs in photoacoustic-imaging-guided photothermal therapy for orthotopic liver cancer treatment in the NIR-II window.

Spirobifluorene Mediating the Spin-Spin Coupling of Nitronyl Nitroxide Diradicals.

To investigate the mechanism of this spiro conjugation magnetic behavior, we designed and synthesized three diradicals─22'SBF-NN, 44'SBF-NN, and 27SBF-NN. They are bridged by spirobifluorene and nitronyl nitroxide (NN) diradicals as the spin centers. Notably, by SQUID and electron paramagnetic resonance (EPR) zero-field splitting data analyses, the 22'SBF-NN and 27SBF-NN diradicals exhibit intramolecular, distinctly antiferromagnetic (AF) coupling, with 2J(22'SBF-NN)/kB = -5.86 K and 2J(27SBF-NN)/kB = -24.6 K, respectively. The AF of 22'SBF-NN is opposite to that predicted by the spin density alternation rule based on Hund's rule. Diradical intramolecular conjugation coupling bridged by spiro-carbon conjugation is discussed, in which the 22'SBF-NN is smaller than that of 27SBF-NN, corresponding to the room-temperature EPR characterization. This spiro conjugation is weaker than the traditional planar conjugation and generally leads to a weaker spin-spin coupling in the helical biradical molecule. The EPR spectrum of the 44'SBF-NN diradical shows a deformed nine-line curve, indicating intramolecular exchange coupling. The density functional theory calculation gives a very weak coupling constant of 2Jcalc/kB = 0.06 K, with ferromagnetic (FM) interaction as the proof, which is consistent with the spin-polarized prediction. Further analysis of magnetic susceptibility χm and VT-EPR data shows that there is indeed an extremely weak FM interaction in the 44' position diradical. We find the bridge, which is a 44' substituted SBF structure, blocks the conjugation and contains a larger twist in steric hindrance, which also hampers sufficient spin density delocalization, resulting in a much weaker spin coupling interaction. Combined with the analysis of molecular orbital calculation results, the anomalous intramolecular AF coupling mechanism of 22'SBF-NN is further explained.

Benchmarking of Density Functionals for the Description of Optical Properties of Newly Synthesized π-Conjugated TADF Blue Emitters.

Computational modeling of the optical characteristics of organic molecules with potential for thermally activated delayed fluorescence (TADF) may assist markedly the development of more efficient emitting materials for organic light-emitting diodes. Recent theoretical studies in this area employ mostly methods from density functional theory (DFT). In order to obtain accurate predictions within this approach, the choice of a proper functional is crucial. In the current study, we focus on testing the performance of a set of DFT functionals for estimation of the excitation and emission energy and the excited singlet-triplet energy gap of three newly synthesized compounds with capacity for TADF. The emitters are designed specifically to enable charge transfer by π-electron conjugation, at the same time possessing high-energy excited triplet states. The functionals chosen for testing are from various groups ranging from gradient-corrected through global hybrids to range-separated ones. The results show that the monitored optical properties are especially sensitive to how the long-range part of the exchange energy is treated within the functional. The accurate functional should also be able to provide well balanced distribution of the π-electrons among the molecular fragments. Global hybrids with moderate (less than 0.4) share of exact exchange (B3LYP, PBE0) and the meta-GGA HSE06 are outlined as the best performing methods for the systems under study. They can predict all important optical parameters correctly, both qualitatively and quantitatively.

Frequency of synchronous malignant liver lesions initially detected by ultrasound in patients with newly diagnosed underlying non-hematologic malignant disease: a retrospective study in 434 patients.

INTRODUCTION: This study described the frequency of malignant synchronous focal liver lesions (FLLs) in patients with newly diagnosed non-hematologic malignant disease. METHODS: From June 2013 to January 2017, 434 patients with synchronous FLLs and newly diagnosed underlying malignant disease were included in the study. The diagnosis of the FLLs was made by histology and/or contrast-enhanced imaging. The final medical report was used for analysis in the study. RESULTS: Of the 434 liver lesions, 258 (59.4%) were malignant and 176 (40.6%) benign. All malignant lesions were metastases. The benign liver lesions were comprised of 93 cysts (21.4%), 52 hemangiomas (12.0%), 20 focal fatty sparing (4.6%), 4 focal nodular hyperplasia (0.9%), 3 unspecified benign lesions (0.7%), 2 regenerative nodules (0.5%), 1 calcification (0.2%), and 1 adenoma (0.2%). Diseases with the highest percentage frequency of synchronous malignant FLLs were cholangiocarcinoma with 86.7%, neuroendocrine tumor with 72.7%, and pancreatic carcinoma with 72.0%. Gastric carcinoma (33.3%), breast carcinoma (44.4%), and urothelial cell carcinoma (45.5%) were the diseases with the lowest percentage frequency of synchronous malignant FLLs. CONCLUSION: In total, the frequency of malignant synchronous FLLs in newly diagnosed non-hematologic malignant disease was 59.4%. In particular, cholangiocarcinoma, neuroendocrine tumor, and pancreatic carcinoma were the diseases with the highest rate of synchronous malignant FLLs.

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.

On-Surface Dehydro-Diels-Alder Reaction of Dibromo-bis(phenylethynyl)benzene.

On-surface synthesis under ultrahigh vacuum conditions is a powerful tool to achieve molecular structures that cannot be accessed via traditional wet chemistry. Nevertheless, only a very limited number of chemical reactions out of the wide variety known from solution chemistry have been reported to proceed readily on atomically flat substrates. Cycloadditions are a class of reactions that are particularly important in the synthesis of sp2-hybridized carbon-based nanostructures. Here, we report on a specific type of [4 + 2] cycloaddition, namely, a dehydro-Diels-Alder (DDA) reaction, performed between bis(phenylethynyl)-benzene precursors on Au(111). Unlike a Diels-Alder reaction, DDA exploits ethynyl groups to achieve the formation of an extra six-membered ring. Despite its extensive use in solution chemistry for more than a century, this reaction has never been reported to occur on surfaces. The specific choice of our precursor molecule has led to the successful synthesis of benzo- and naphtho-fused tetracene and heptacene products bearing styryl groups, as confirmed by scanning tunneling microscopy and noncontact atomic force microscopy. The two products arise from dimerization and trimerization of the precursor molecules, respectively, and their observation opens perspectives to use DDA reactions as a novel on-surface synthesis tool.

Dithienopyrrole Derivatives with Nitronyl Nitroxide Radicals and Their Oxidation to Cationic High-Spin Molecules.

Three 1 N-phenyl nitronyl nitroxide (NN) 4-substituted dithieno[3,2-b:2',3'-d]pyrrole (DTP) derivatives with R1=4-phenyl-, 4H-, and 4-methylthiothiophenyl- (R1 2 DTP-Ph-NN, R1 =H, Ph and MeSTh) were designed, synthesized and characterized. The electrochemical properties were studied by cyclic voltammetry (CV). All the molecules exhibited two main oxidation peaks, first for radical cation and next for dication formation. The cation and dication formation were also confirmed by UV/Vis absorption spectroscopy for Ph2 DTP-Ph-NN and MeSTh2 DTP-Ph-NN titrated with tris(4-bromophenyl)aminiumhexachloroantimonate (magic blue). In addition, the cation and dication formation were verified by EPR spectroscopy. Finally, the exchange interactions (J/kB ) of NN and radical cation were calculated by DFT studies.

Three-Dimensional Pyrene-Fused N-Heteroacenes.

Four three-dimensional (3D) pyrene-fused N-heteroacenes (P1-P4) are designed and synthesized. From P1 to P4, their lengths are extended in an iterative way, where the thiadiazole unit can be reduced to diamine and the obtained diamines can be further condensed with the diketones with a thiadiazole unit. Compared to their two-dimensional counterparts, the solubility of these 3D pyrene-fused N-heteroacenes is improved by this 3D covalent linkage with two-dimensional units. The diameters of P1-P4 are 3.66, 6.06, 8.48 and 10.88 nm, respectively, and these 3D molecules are characterized by 1H, 13C and 2D NMR, MS, UV-vis, PL and CV spectra. Our strategy shows a promising way to large 3D pyrene-fused N-heteroacenes.

Open-Shell Nonbenzenoid Nanographenes Containing Two Pairs of Pentagonal and Heptagonal Rings.

Nonbenzenoid carbocyclic rings are postulated to serve as important structural elements toward tuning the chemical and electronic properties of extended polycyclic aromatic hydrocarbons (PAHs, or namely nanographenes), necessitating a rational and atomically precise synthetic approach toward their fabrication. Here, using a combined bottom-up in-solution and on-surface synthetic approach, we report the synthesis of nonbenzenoid open-shell nanographenes containing two pairs of embedded pentagonal and heptagonal rings. Extensive characterization of the resultant nanographene in solution shows a low optical gap, and an open-shell singlet ground state with a low singlet-triplet gap. Employing ultra-high-resolution scanning tunneling microscopy and spectroscopy, we conduct atomic-scale structural and electronic studies on a cyclopenta-fused derivative on a Au(111) surface. The resultant five to seven rings embedded nanographene displays an extremely narrow energy gap of 0.27 eV and exhibits a pronounced open-shell biradical character close to 1 (y0 = 0.92). Our experimental results are supported by mean-field and multiconfigurational quantum chemical calculations. Access to large nanographenes with a combination of nonbenzenoid topologies and open-shell character should have wide implications in harnessing new functionalities toward the realization of future organic electronic and spintronic devices.

Planar Benzo[1,2- b:4,5- b']dithiophene Derivatives Decorated with Nitronyl and Imino Nitroxides.

Four weakly antiferromagnetic interacting biradicals of benzo[1,2- b:4,5- b']dithiophene (BDT) and BDT extended with two thiophenes (BDTTh2) linked with nitronyl and imino nitroxides (NN and IN) as BDT-NN, BDT-IN, BDTTh2-NN, and BDTTh2-IN were designed, synthesized, and characterized. Short intermolecular π-π distances were found (3.42 Å) for BDT-NN, whereas larger ones were found for BDT-IN (3.54 Å) and BDTTh2-NN (3.67 Å), respectively. Intramolecular magnetic interaction ( Jintra,exp/ kB) of BDT-NN (-26 K) is much larger than for BDT-IN (-5.3 K), while it is reduced for the dithiophene-extended molecule BDTTh2-NN (-2.3 K). Intermolecular interactions ( zJinter,exp/ kB) of BDT-NN (-6.5 K) and BDT-IN (-6.0 K) are stronger than for BDTTh2-NN (-4.6 K). Such large intermolecular couplings resulting from good π-stacking mark BDT-IN and BDTTh2-NN as promising crystalline materials with similar sized Jintra and Jinter. In addition, we also extracted a coupling within the chain of Jchain/ kB = -2.2 K and a coupling between the chains of zJinterchain = -1.5 K for BDTTh2-NN by a Heisenberg chain model. Intra- and intermolecular interactions and spin densities were examined by DFT studies.

Temperature-Dependent Intramolecular Spin Coupling Interactions of a Flexible Bridged Nitronyl Nitroxide Biradical in Solution.

A biradical consisting of two nitronyl nitroxide (NN) radicals bridged by diphenyl-hexaethylene glycol chain [phenyl-O-(CH2CH2O)6-phenyl (GBN1)] was synthesized and investigated using electron paramagnetic resonance (EPR) spectroscopy in solution at different temperature ranges. The reversible temperature dependence behavior of spin coupling exchange is comprehensively reflected by the different lifetime of conformations due to a tumbling motion of the flexible hexaethylene glycol chain. The influences of different solvent on the exchange interactions between the radical entities are described by a two-conformational model, which was, for the first time, applied for di-NN molecule and revealed the thermodynamic parameters enthalpy and entropy (ΔH and ΔS) of the conformational changes. The positive value of enthalpy indicates lower energy of the stretched form (as calculated) compared to the bent form. The transition enthalpy in polar MeCN is larger than in toluene and the positive entropy sign indicates more chain conformation options in the bent state. The magnetic properties of this molecule were investigated in solid state by magnetization studies and EPR spectroscopy.

Layered Thiadiazoloquinoxaline-Containing Long Pyrene-Fused N-Heteroacenes.

Three thiadiazoloquinoxaline-containing long pyrene-fused N-heteroacenes with 8, 13, and 18 rings were designed and synthesized. They show high electron affinities (EAs) of approximately 4.1 eV, which were derived from the onset of the reduction peaks in cyclic voltammetry. Crystal structure analysis revealed in-plane extension through close contacts between thiadiazole units as well as layered packing, enabling in-plane and interlayer electron transport. Organic field-effect transistor devices provided electron mobilities, which suggest a potential way to enhance the charge transport in long N-heteroacenes.

Edge Functionalization of Structurally Defined Graphene Nanoribbons for Modulating the Self-Assembled Structures.

Edge functionalization of bottom-up synthesized graphene nanoribbons (GNRs) with anthraquinone and naphthalene/perylene monoimide units has been achieved through a Suzuki coupling of polyphenylene precursors bearing bromo groups, prior to the intramolecular oxidative cyclo-dehydrogenation. High efficiency of the substitution has been validated by MALDI-TOF MS analysis of the functionalized precursors and FT-IR, Raman, and XPS analyses of the resulting GNRs. Moreover, AFM measurements demonstrated the modulation of the self-assembling behavior of the edge-functionalized GNRs, revealing that GNR-PMI formed an intriguing rectangular network. This result suggests the possibility of programming the supramolecular architecture of GNRs by tuning the functional units.