RESUMEN
Synthesis of conjugated compounds with unusual shape-persistent structures remains a challenge. Herein, utilizing thermodynamically reversible intermolecular Friedel-Crafts alkylation, a dynamic covalent chemistry (DCC) reaction, we facilely synthesized a figure-eight shaped macrocycle FEM and cage molecules CATPA/CACz. X-ray crystallographic analysis confirmed the chemical geometries of tetracation FEM4+(PF6 -)4 and hexacation CACz6+(SbF6 -)6. FEM and CATPA displayed higher photoluminescence quantum yield in solid states compared to that in solution, whereas CACz gave the reverse result. DFT calculations showed that fluorescence-related frontier molecular orbital profiles are mainly localized on their arms consisting of a p-quinodimethane (p-QDM) unit and two benzene rings of triphenylamine or carbazole. Owing to their space-confined structures, variable-temperature 1H NMR measurements showed that FEM, CATPA and FEM4+ have intramolecular restricted motion of phenyl rings on their chromophore arms. Accordingly, FEM and CATPA with flexible triphenylamine subunits displayed aggregation-induced emission behavior (AIE), whereas CACz with a rigid carbazole subunits structure showed no AIE behavior.
RESUMEN
We report the synthesis of the bis(benzooxa)-2,6-anthraquinodimethane (BAQ) derivative and its bisindeno fused analogue BIBAQ. We found bisindeno fusion on the quinoidal zigzag edge of BAQ results in decreased diradical character and corresponding increased photostability. Furthermore, BAQ could only be oxidized into its cationic species, while BIBAQ showed balanced redox properties.
RESUMEN
Antiaromatic moieties fused in polycyclic π-conjugated molecules usually exhibit strong localized antiaromaticiy. Herein, we reported the synthesis and properties of a bisazapentalene dication (BAP2+) obtained from in situ two-electron oxidation of neutral species 8. Noteworthily, it possesses global aromaticity and an open-shell singlet ground state. This study underlines the importance of heteroatoms in determining the delocalization of π-electrons and the aromaticity of molecules in their oxidized states.
RESUMEN
Creating atomically precise quantum architectures with high digital fidelity and desired quantum states is an important goal in a new era of quantum technology. The strategy of creating these quantum nanostructures mainly relies on atom-by-atom, molecule-by-molecule manipulation or molecular assembly through non-covalent interactions, which thus lack sufficient chemical robustness required for on-chip quantum device operation at elevated temperature. Here, we report a bottom-up synthesis of covalently linked organic quantum corrals (OQCs) with atomic precision to induce the formation of topology-controlled quantum resonance states, arising from a collective interference of scattered electron waves inside the quantum nanocavities. Individual OQCs host a series of atomic orbital-like resonance states whose orbital hybridization into artificial homo-diatomic and hetero-diatomic molecular-like resonance states can be constructed in Cassini oval-shaped OQCs with desired topologies corroborated by joint ab initio and analytic calculations. Our studies open up a new avenue to fabricate covalently linked large-sized OQCs with atomic precision to engineer desired quantum states with high chemical robustness and digital fidelity for future practical applications.
RESUMEN
Fully conjugated macrocycles containing benzenoid rings rarely show global aromaticity/antiaromaticity. Herein, we report an annulene-like macrocycle CBTT and its S,S-dioxidized macrocycle DOCBTT with alternative quinoidal thiophene/1,1-dioxide thiophene and triphenyl amine moieties. They both showed temperature-dependent intramolecular dynamics and global antiaromatic character with 32π electrons at low temperature. However, CBTT and DOCBTT have different conjugated pathways.
RESUMEN
A tetraindeno-fused bis(anthraoxa)quinodimethane RBR with nine consecutively fused six-membered rings in a row was synthesized. Its structure was confirmed by X-ray crystallographic analysis and NMR measurement. Compared with an unfused analogue ABA, the indeno fusion onto the zigzag edges not only enhanced the photostability but also dramatically tuned the electronic properties. Due to the existence of two rubicene units, RBR can also be readily reduced to form a radical anion and dianion.
RESUMEN
The synthesis of peri-fused acenes (peri-acenes) with two or more rows is challenging due to their intrinsic open-shell diradical character. Herein, we report the isolation of a derivative (4) of [4,3]peri-acene in crystalline form. The parent [4,3]peri-acene, containing three rows of tetracene, has a large diradical character (y0 =94.8 %) originating from aromatic stabilization. Due to kinetic blocking, 4 showed a reasonable stability with a half-life time of ≈157â h under ambient conditions. Its structure was determined by X-ray crystallographic analysis, and bond-length analysis revealed eight localized Clar's sextets. 4 exhibited an open-shell singlet ground state with a narrow electrochemical energy gap (1.13â eV) and a small singlet-triplet energy gap (-0.57â kcal mol-1 from SQUID measurements). Its electronic properties are compared with previously reported peri-tetracene and teranthene derivatives.
RESUMEN
Synthesis of a carbon nanobelt (CNB) is a very challenging task in organic chemistry. Herein, we report the successful synthesis of an octabenzo[12]cyclacene based CNB (6), which can be regarded as a sidewall fragment of a (12,0) carbon nanotube. The key intermediate compound, a tetraepoxy nanobelt (5), was first synthesized by Diels-Alder reaction, and subsequent reductive aromatization gave the fully conjugated CNB 6. X-ray crystallographic analysis unambiguously confirmed the belt-shaped structure of 6. 1 Hâ NMR spectrum and theoretical calculations (ACID, NICS, and 2D/3D ICSS) revealed localized aromaticity and stronger shielding chemical environment in the inner region of the belt. The optical properties (absorption and emission) of 6 were studied and correlated to its electronic structure. Strain analysis indicates that the phenyl substituents at the zigzag edges are crucial to the successful synthesis of 6. This report presents a new strategy towards highly strained CNBs.
RESUMEN
Incorporation of a non-hexagonal ring into a nanographene framework can lead to new electronic properties. During the attempted synthesis of naphthalene-bridged double [6]helicene and heptagon-containing nanographene by the Scholl reaction, an unexpected azulene-embedded nanographene and its triflyloxylated product were obtained, as confirmed by X-ray crystallographic analysis and 2D NMR spectroscopy. A 5/7/7/5 ring-fused substructure containing two formal azulene units is formed, but only one of them shows an azulene-like electronic structure. The formation of this unique structure is explained by arenium ion mediated 1,2-phenyl migration and a naphthalene to azulene rearrangement reaction according to an in-silico study. This report represents the first experimental example of the thermodynamically unfavorable naphthalene to azulene rearrangement and may lead to new azulene-based molecular materials.
RESUMEN
π-Conjugated macrocycles containing all-benzenoid rings usually show local aromaticity, but reported herein is the macrocycle CBQT, containing alternating para-quinodimethane and triphenylamine units displaying annulene-like anti-aromaticity at low temperatures as a result of structural rigidity and participation of the bridging nitrogen atoms in π-conjugation. It was easily synthesized by intermolecular Friedel-Crafts alkylation followed by oxidative dehydrogenation. X-ray crystallographic structures of CBQT, as well as those of its dication, trication, and tetracation were obtained. The dication and tetracation exhibited global aromaticity and antiaromaticity, respectively, as confirmed by NMR measurements and theoretical calculations. Both the dication and tetracation possess open-shell singlet ground states, with a small singlet-triplet gap.
RESUMEN
Linear quinodimethane-embedded acene analogue 9L was synthesized, and its quinoidal structure was confirmed by X-ray crystallographic analysis. The multiple oxidation states of 9L could be achieved. Its dication is a triplet diradical, and its tetracation can be regarded as the isoelectronic structure of the nonacene, which was validated by experiments and theoretical calculations.
RESUMEN
We report the challenging synthesis of two very long bis(anthraoxa)quinodimethanes with nine (ABA) and ten (ANA) consecutively fused six-membered rings. The former is stable with negligible diradical character, while the latter with a moderate diradical character ( y0 = 25.0%) is reactive and an unexpected trifluoroacetic substituted product (ANA-TFA) was isolated. X-ray crystallographic analysis revealed a planar backbone with a typical quinoidal character for both. Their dications can be regarded as the isoelectronic structures of the respective nonacene and decacene. The dication ABA2+ and dianion ABA2- are open-shell singlet diradicaloids, while the longer dication ANA-TFA2+ and dianion ANA2- have closed-shell ground state, which can be explained by the different intramolecular Coulomb interactions. Both dianions have a bent backbone and can be considered as an isoelectronic structure of the tetraanion of nonacene and decacene, respectively.
RESUMEN
Cyclopenta ring fused bisanthene and its charged species were synthesized. The neutral compound has an open-shell singlet ground state and displays global anti-aromaticity. The dication also exhibits singlet diradical character but has a unique [10]annulene-within-[18]annulene global aromatic structure. The dianion is closed-shell singlet in the ground state and shows global aromaticity with 22 πâ electrons delocalized on the periphery. These findings prrovide new insight into the design and properties of global aromatic/anti-aromatic systems based on π-conjugated polycyclic hydrocarbons.
RESUMEN
Two BODIPY-substituted anthroxyl radicals were investigated. The one with two ethyl substituents (2Et-BO-An-O) is sensitive to air and silica gel due to the lack of sufficient kinetic blocking, while another one with four methyl substituents (4Me-BO-An-O) shows high stability. The structure of the latter was fully characterized by X-ray crystallographic analysis and electron-spin resonance spectra. 4Me-BO-An-O was subjected to react with various reactive oxygen/nitrogen species (ROS/RNS) and selective fluorescence turn-on detection of a hydroxyl radical was achieved, validating the concept of "using stable radicals to detect ROS/RNS".
RESUMEN
Understanding the mechanism of singlet exciton fission, in which a singlet exciton separates into a pair of triplet excitons, is crucial to the development of new chromophores for efficient fission-sensitized solar cells. The challenge of controlling molecular packing and energy levels in the solid state precludes clear determination of the singlet fission pathway. Here, we circumvent this difficulty by utilizing covalent dimers of pentacene with two types of side groups. We report rapid and efficient intramolecular singlet fission in both molecules, in one case via a virtual charge-transfer state and in the other via a distinct charge-transfer intermediate. The singlet fission pathway is governed by the energy gap between singlet and charge-transfer states, which change dynamically with molecular geometry but are primarily set by the side group. These results clearly establish the role of charge-transfer states in singlet fission and highlight the importance of solubilizing groups to optimize excited-state photophysics.
RESUMEN
Higher order acenes (i.e., acenes longer than pentacene) and extended zethrenes (i.e., zethrenes longer than zethrene) are theoretically predicted to have an open-shell singlet ground state, and the radical character is supposed to increase with extension of molecular size. The increasing radical character makes the synthesis of long zethrenes and acenes very challenging, and so far, the longest reported zethrene and acene derivatives are octazethrene and nonacene, respectively. In addition, there is a lack of fundamental understanding of the differences between these two closely related open-shell singlet systems. In this work, we report the first synthesis of a challenging nonazethrene derivative, HR-NZ, and its full structural and physical characterizations including variable temperature NMR, ESR, SQUID, UV-vis-NIR absorption and electrochemical measurements. Compound HR-NZ has an open-shell singlet ground state with a moderate diradical character (y0 = 0.48 based on UCAM-B3LYP calculation) and a small singlet-triplet gap (ΔES-T = -5.2 kcal/mol based on SQUID data), thus showing magnetic activity at room temperature. It also shows amphoteric redox behavior, with a small electrochemical energy gap (1.33 eV). Its electronic structure and physical properties are compared with those of Anthony's nonacene derivative JA-NA and other zethrene derivatives. A more general comparison between higher order acenes and extended zethrenes was also conducted on the basis of ab initio electronic structure calculations, and it was found that zethrenes and acenes have very different spatial localization of the unpaired electrons. As a result, a faster decrease of singlet-triplet energy gap and a faster increase of radical character with increase of the number of benzenoid rings were observed in zethrene series. Our studies reveal that spatial localization of the frontier molecular orbitals play a very important role on the nature of radical character as well as the excitation energy.
RESUMEN
Extended bis(benzothia)quinodimethanes and their dications were synthesized as stable species. The neutral compounds mainly have a quinoidal structure in the ground state but show increased diradical character with extension of the central quinodimethane unit. The dications exhibit similar electronic absorption spectra, NMR spectra, NICS values, and diatropic ring currents to their aromatic all-carbon acene analogues and thus can be regarded as genuine isoelectronic structures of pentacene, hexacene, and heptacene, respectively. Our research gave some insights into the design and synthesis of stable longer acene analogues.
RESUMEN
Acene-based materials have promising applications for organic electronics but the major constrain comes from their poor stability. Herein a new strategy to stabilize reactive acenes, by fusion of an anti-aromatic pentalene unit onto the zigzag edges of two acene units to form a Z-shaped acene dimer, is introduced. The Z-shaped acene dimers are extremely stable and show a small energy gap resulting from intramolecular donor-acceptor interactions. X-ray crystallographic analysis revealed their unique geometry and one-dimensional slip-stack columnar structure. Besides optical and electrochemical characterizations, solution-processed field-effect transistors were also fabricated.
