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Radicals of the lightest group 13 element, boron, are well established and observed in numerous forms. In contrast to boron, radical chemistry involving the heavier group 13 elements (aluminum, gallium, indium, and thallium) remains largely underexplored, primarily attributed to the formidable synthetic challenges associated with these elements. Herein, we report the synthesis and isolation of planar and twisted conformers of a doubly CAAC (cyclic alkyl(amino)carbene)‐radical‐substituted dialane. Extensive characterization through spectroscopic analyses and X‐ray crystallography confirms their identity, while quantum chemical calculations support their open‐shell nature and provide further insights into their electronic structures. The dialane‐connected diradicals exhibit high susceptibility to oxidation, as evidenced by electrochemical measurements and reactions with o‐chloranil and a variety of organic azides. This study opens a previously uncharted class of dialuminum systems to study, broadening the scope of diradical chemistry and its potential applications. [ABSTRACT FROM AUTHOR]

We report the preparation of a new organic σ‐donor with a C6H4‐linker between an N‐heterocyclic carbene (NHC) and an exocyclic methylidene group, which we term N‐heterocyclic quinodimethane (NHQ). The aromatization of the C6H4‐linker provides a decisive driving force for the reaction of the NHQ with an electrophile and renders the NHQ significantly more basic than analogous NHCs or N‐heterocyclic olefins (NHOs), as shown by DFT computations and competition experiments. In solution, the NHQ undergoes an unprecedented dehydrogenative head‐to‐head dimerization by C−C coupling of the methylidene groups. DFT computations indicate that this reaction proceeds via an open‐shell singlet pathway revealing the diradical character of the NHQ. The product of this dimerization can be described as conjugated N‐heterocyclic bis‐quinodimethane, which according to cyclic voltammetry is a strong organic reducing agent (E1/2=−1.71 V vs. Fc/Fc+) and exhibits a remarkable small singlet–triplet gap of ΔES→T=4.4 kcal mol−1. [ABSTRACT FROM AUTHOR]

Herein, reactivity studies of a cyclic bis‐hydridostannylene [(ADC)SnH]2 (1‐H2) (ADC=PhC{(NDipp)C}2; Dipp=2,6‐iPr2C6H3) with various unsaturated organic substrates are reported. Reactions of terminal alkynes (RC≡CH) with 1‐H2 afford mixed acetylide‐vinyl‐functionalized bis‐stannylenes via dehydrogenation and hydrostannylation. Treatment of 1‐H2 with PhC≡CCH3 gives a unique distannabarrelene via dehydrogenative C(sp3)−H stannylation and hydrostannylation of the C≡CCH3 moiety. 1‐H2 undergoes dehydrogenative [2+2]‐cycloaddition reactions with diphenylacetylene, azobenzene, acetone, benzophenone, and benzaldehyde to form the 1,4‐distannabarrelene derivatives. The elimination of H2 in these reactions suggests the masked‐diradical property of 1‐H2. In fact, these [2+2]‐cycloaddition products are also accessible on treatments of the Sn(I) diradicaloid [(ADC)Sn]2 (1) with appropriate reagents. All compounds have been characterized by multinuclear NMR spectroscopy and single crystal X‐ray diffraction. Moreover, the catalytic activity of 1‐H2 has been shown for the hydroboration of unsaturated substrates. [ABSTRACT FROM AUTHOR]

Phosphorus‐centered disbiradicals, in which the radical sites exist as individual spin doublets with weak spin‐spin interaction have not been known so far. Starting from monoradicals of the type [⋅P(μ‐NTer)2P−R], we have now succeeded in linking two such monoradical phosphorus centers by appropriate choice of a linker. To this end, biradical [⋅P(μ‐NTer)2P⋅] (1) was treated with 1,6‐dibromohexane, affording the brominated species {Br[P(μ‐NTer)]2}2C6H12 (3). Subsequent reduction with KC8 led to the formation of the disbiradical {⋅[P(μ‐NTer)]2}2C6H12 (4) featuring a large distance between the radical phosphorus sites in the solid state and formally the highest biradical character observed in a P‐centered biradical so far, approaching 100 %. EPR spectroscopy revealed a three‐line signal in solution with a considerably larger exchange interaction than would be expected from the molecular structure of the single crystal. Quantum chemical calculations revealed a highly dynamic conformational space; thus, the two radical sites can approach each other with a much smaller distance in solution. Further reduction of 4 resulted in the formation of a potassium salt featuring the first structurally characterized P‐centered distonic radical anion (5−). Moreover, 4 could be used in small molecule activation. [ABSTRACT FROM AUTHOR]

Radicals based on arylamine cyclophanes can be used as functional materials and show application potential in fields such as synthetic chemistry, molecular electronic components, organic light-emitting diodes, and catalytic chemistry. Using a Buchwald–Hartwig palladium-catalyzed aryl halide amination method, we synthesized a series of neutral hexaazacyclophane compounds 1–3 with different substituents in the meta–meta–meta positions of the phenyl rings. Three characteristic high-spin hexaazacyclophane diradical dications were obtained by two-electron oxidation using AgSbF6: 12·+•2[SbF6]−, 22·+•2[SbF6]−, and 32·+•2[SbF6]−. The electronic structures and physical properties of these compounds were then investigated by 1H and 13C nuclear magnetic resonance spectroscopy, cyclic voltammetry, electron paramagnetic resonance spectroscopy, superconducting quantum interferometry, ultraviolet–visible spectroscopy, and density functional theory calculations. The findings provide new ideas for designing radical species with novel physical properties and electronic structures. Importantly, the obtained radical species are not sensitive to air, making them valuable functional materials for practical applications. [ABSTRACT FROM AUTHOR]

The dinitrene 2,3,5,6‐tetrafluoro‐1,4‐phenylenedinitrene was synthesized by photolysis of matrix‐isolated 1,4‐diazido‐2,3,5,6‐tetrafluorobenzene at 365 or 405 nm in high yields at cryogenic temperatures and characterized by FT‐IR, UV‐Vis, and EPR spectroscopy. The electronic structure of the dinitrene is described best as a quinoidal diradical with an open‐shell singlet ground state and a triplet state laying only 650 ± 5 cal/mol higher in energy. Irradiation with λ = 254 nm results in fragmentation of the dinitrene into FCCF and several olefins which on prolonged photolysis fragment into FCCCN, FCCNC, and FCN. [ABSTRACT FROM AUTHOR]

Two series of regioisomeric dicyanomethylene substituted dithienodiazatetracenes with formal para‐ or ortho‐quinodimethane subunits were synthesized and characterized. Whereas the para‐isomers (p‐n, diradical index y0=0.01) are stable and isolable, the ortho‐isomer (y0=0.98) dimerizes into a covalent azaacene cage. Four elongated σ‐CC bonds are formed and the former triisopropylsilyl(TIPS) ‐ethynylene groups transformed into cumulene units. The azaacene cage dimer (o‐1)2 was characterized by X‐ray single crystal structure analysis and temperature‐dependent infrared (IR), electron paramagnetic resonance (EPR, solid‐state), nuclear magnetic resonance (NMR) and ultraviolet‐visible (UV/Vis) spectroscopies (solution) indicating reformation of o‐1. [ABSTRACT FROM AUTHOR]

Radicals based on arylamine cyclophanes can be used as functional materials and show application potential in fields such as synthetic chemistry, molecular electronic components, organic light-emitting diodes, and catalytic chemistry. Using a Buchwald–Hartwig palladium-catalyzed aryl halide amination method, we synthesized a series of neutral hexaazacyclophane compounds 1–3 with different substituents in the meta–meta–meta positions of the phenyl rings. Three characteristic high-spin hexaazacyclophane diradical dications were obtained by two-electron oxidation using AgSbF6: 12·+•2[SbF6]−, 22·+•2[SbF6]−, and 32·+•2[SbF6]−. The electronic structures and physical properties of these compounds were then investigated by 1H and 13C nuclear magnetic resonance spectroscopy, cyclic voltammetry, electron paramagnetic resonance spectroscopy, superconducting quantum interferometry, ultraviolet–visible spectroscopy, and density functional theory calculations. The findings provide new ideas for designing radical species with novel physical properties and electronic structures. Importantly, the obtained radical species are not sensitive to air, making them valuable functional materials for practical applications.

Photoinitiated radical chemistry has proven to be useful for breaking covalent bonds within many biomolecules in the gas phase. Herein, we demonstrate that radical chemistry is useful for bond synthesis in the gas phase. Single peptides containing two cysteine residues capped with propylmercaptan (PM) often form disulfide bonds following ultraviolet excitation at 266 nm and loss of both PM groups. Similarly, noncovalently bound peptide pairs where each peptide contains a single cysteine residue can be induced to form disulfide bonds. Comparison with disulfide bound species sampled directly from solution yields identical collisional activation spectra, suggesting that native disulfide bonds have been recapitulated in the gas phase syntheses. Another approach utilizing radical chemistry for covalent bond synthesis involves creation of a reactive diradical that can first abstract hydrogen from a target peptide, creating a new radical site, and then recombine the second radical with the new radical to form a covalent bond. This chemistry is illustrated with 2-(hydroxymethyl-3,5-diiodobenzoate)-18-crown-6 ether, which attaches noncovalently to protonated primary amines in peptides and proteins. Following photoactivation and crosslinking, the site of noncovalent adduct attachment can frequently be determined. The ramifications of these observations on peptide structure and noncovalent attachment of 18-crown-6-based molecules is discussed.

Photoinitiated radical chemistry has proven to be useful for breaking covalent bonds within many biomolecules in the gas phase. Herein, we demonstrate that radical chemistry is useful for bond synthesis in the gas phase. Single peptides containing two cysteine residues capped with propylmercaptan (PM) often form disulfide bonds following ultraviolet excitation at 266 nm and loss of both PM groups. Similarly, noncovalently bound peptide pairs where each peptide contains a single cysteine residue can be induced to form disulfide bonds. Comparison with disulfide bound species sampled directly from solution yields identical collisional activation spectra, suggesting that native disulfide bonds have been recapitulated in the gas phase syntheses. Another approach utilizing radical chemistry for covalent bond synthesis involves creation of a reactive diradical that can first abstract hydrogen from a target peptide, creating a new radical site, and then recombine the second radical with the new radical to form a covalent bond. This chemistry is illustrated with 2-(hydroxymethyl-3,5-diiodobenzoate)-18-crown-6 ether, which attaches noncovalently to protonated primary amines in peptides and proteins. Following photoactivation and crosslinking, the site of noncovalent adduct attachment can frequently be determined. The ramifications of these observations on peptide structure and noncovalent attachment of 18-crown-6-based molecules is discussed.

Null [ABSTRACT FROM AUTHOR]

Synthesis and structural characterization of a family of germanium-dioxolene complexes with ditopic N-donor ligands (L1-L5) (L1 = 1,2-bis(pyridin-2-ylmethylene)hydrazine L2 = 1,6-bis-(pyridin-2-yl)-2,5-diaza-1,5-heхаdiene, L3 = N,N-bis(pyridin-2-ylmethylene)-1,4-benzenediamine, L4 = N,N-bis(pyridin-2-ylmethylene)-(biphenyl)-4,4-diamine, L5 = 2,2'-azopyridine) is reported. The reaction of germanium bis-catecholate with bridging ligands L1 - L4, differing by the nature of the linker between pyridine sites gives rise to dinuclear digermanium complexes (36Cat2Ge)2L1-4 (36Cat = dianion of 3,6-di-tert-butylcatechol) 1-4 of DMAMD type (donor-metal-acceptor-metal-donor) with a charge transfer in the UV-Vis region. In opposite, the interaction of the 36Cat2Ge with 2,2'-azopyridine (L5) results in the two-electron transfer from the donor 36Cat2- ligands to the azopyridine bridge forming stable open-shell complex 5 [(36SQ)(36CatGe)]2(L5)2- (36SQ = radical-anionic semiquinonate ligand). Molecular structures of compounds 3 and 5 were determined by single crystal X-ray diffraction analysis. Electronic structures of complexes 1-5 were studied by means of DFT calculations., (© 2024 Wiley‐VCH GmbH.)

The multifaceted little Na−B bond in NaBH3‐ cluster has been the subject of many recent studies. Many proposals have been put forward for the complete understanding of the chemical bonding in NaBH3‐ cluster. However, none of the studies provided a complete picture. Herein, the missing recipe of the chemical bonding in NaBH3‐ cluster has been identified which completes the description. Our calculations reveal that the chemical bonding in NaBH3‐ cluster is more multifaceted than ever thought. Our finding suggests that the NaBH3‐ cluster features a Na−B one electron bond which is assisted by three 3‐centre‐2‐electron Na‐B−H bond. Detailed topological analyses of electron density and electron localization function at the correlated level reveal such a bonding situation. This missing 3‐centre‐2‐electron Na‐B−H bond completes the description of chemical bonding in NaBH3‐ cluster which is at‐per with the well established bonding scenario for electron deficient compounds. Similar bonding scenario is observed in KBH3−, CuBH3‐ and AuBH3− clusters, further lending support to the complete picture of bonding. [ABSTRACT FROM AUTHOR]

The parent and radical-modified chitin units are computationally studied and the parent chitin unit possesses closed-shell singlet (CS) state as its ground state. Two radicals (CH3. and CH3CH2.) are chosen to modify the parent chitin unit. Calculations predict that CH3CH2·-modified chitin unit possesses the open-shell brokensymmetry (BS) singlet diradical ground state, different from that CH3·-modified chitin unit is a triplet diradical. That is to say, the magnetic conversion can occur from nonmagnetic exchange coupling to antiferromagnetic(AFM) or ferromagnetic(FM) exchange coupling by means of the radical modification method. The present work helps to get a basic understanding of structures and electronic properties of chitin and its radical-modified derivatives at the atomistic level. Moreover, it also provides a feasible way to design new chitin-based magnetic materials and organic magnetic switches. [ABSTRACT FROM AUTHOR]

A heteroatomic analog of 1,1,2,3,3-pentamethylenepropane, the diradical N-[bis(4,4,5,5-tetramethyl-3-oxide-1-oxyl-4,5-dihydro-1H-imidazol-2-yl)methylene]-2-methylpropane-2-amine oxide (1) with two C(sp2)-bonded nitronyl nitroxide fragments in magnetically concentrated (single crystal) and magnetically diluted (frozen solution) forms was studied by EPR spectroscopy. The longitudinal and transverse relaxation times of diradical 1 in the frozen solution were measured for the first time; a significant difference in the intramolecular exchange interaction was demonstrated for the cases of the single crystal and the frozen solution. The influence of solvation on the value of the intramolecular exchange interaction in this class of compounds was discussed. [ABSTRACT FROM AUTHOR]

The first SnI diradical [(ADCPh)Sn]2 (4) based on an anionic dicarbene (ADCPh={CN(Dipp)}2CPh; Dipp=2,6‐iPr2C6H3) scaffold has been isolated as a green crystalline solid by KC8 reduction of the corresponding bis‐chlorostannylene [(ADCPh)SnCl]2 (3). The six‐membered C4Sn2‐ring of 4 containing six π‐electrons shows a diatropic ring current, thus 4 may also be regarded as the first 1,4‐distannabenzene derivative. DFT calculations suggest an open‐shell singlet (OS) ground state of 4 with a remarkably small singlet–triplet energy gap (ΔEOS–T=4.4 kcal mol−1), which is consistent with CASSCF (ΔES–T=6.6 kcal mol−1 and diradical character y=37 %) calculations. The diradical 4 splits H2 at room temperature to yield the bis‐hydridostannylene [(ADCPh)SnH]2 (5). Further reactivity of 4 has been studied with PhSeSePh and MeOTf. [ABSTRACT FROM AUTHOR]

Quantum chemical methods are useful for probing the energetic viability of chemical mechanisms involved in natural product biosynthesis. Typical computational approaches are described and representative examples of mechanistic studies on radical, pericyclic, and carbocation rearrangement reactions that lead to polycyclic skeletons of complex natural products showcase the utility of such methods in providing understanding and shaping future experimental studies. The importance of inherent substrate reactivity is highlighted and cautions for interpreting computational results are discussed. This article is categorized under:Structure and Mechanism > Reaction Mechanisms and CatalysisTheoretical and Physical Chemistry > Reaction Dynamics and KineticsStructure and Mechanism > Computational Biochemistry and Biophysics [ABSTRACT FROM AUTHOR]

Pyrrolidine is a suitable model substance featuring a five-membered N-heterocycle representing the typical structure of the N-containing compounds in biomass. Previous studies have provided ambiguous arguments on the reaction mechanism of pyrrolidine thermal decomposition. Knowledge on the fate of the most dominant decomposition product, the unstable diradical · CH 2 NHCH 2 · , is lacking. In this work, a high-level potential energy surface of the unimolecular reactions of · CH 2 NHCH 2 · , including isomerization and decomposition channels, was explored. Then, the rate coefficients of various channels were obtained by the RRKM/master equation method over 500–2000 K and 0.001–100 atm. The results show that the thermal stabilization of cyc-C 2 H 5 N is highly favored over other isomerization and decomposition channels. The channels isomerizing to CH 3 NCH 2 , cis-HNCHCH 3 and trans-HNCHCH 3 compete with each other, and the rate constants are at least two orders of magnitude lower than the formation of cyc-C 2 H 5 N. Being thermodynamically unstable, cyc-C 2 H 5 N will mainly isomerize back into the diradical at temperatures ≤ 1200 K at 1 atm or isomerize to cis-HNCHCH 3 when the temperature is higher. To validate the postulated reaction pathways, a pyrolysis experiment of pyrrolidine was conducted in a SiC reactor with a short residence time (40–60 μ s) at 1050 K and 0.263 atm. The experimental result confirms the collisional stabilization of H 2 NCHCH 2 and cyc-C 2 H 5 N + CH 3 NCH 2. The diradical · CH 2 NHCH 2 · was not readily detectable due to its low concentration, which falls below the detection limit of current analytical techniques, while the stabilization of cis-HNCHCH 3 and trans-HNCHCH 3 was not sure because of their extremely low photoionization cross section under the studied energy range. The rate constants of the isomerization and decomposition reactions of diradical · CH 2 NHCH 2 · and cyc-C 2 H 5 N are provided, which are valuable for developing the mechanism for pyrrolidine and deepening our understanding of the mechanism of N-heterocyclic compounds pyrolysis/combustion. [ABSTRACT FROM AUTHOR]

Carbon-centered radicals and diradicaloids based on classical N-heterocyclic carbene (NHC) scaffolds are readily accessible as crystalline solids. The presence of an aryl (Ar) substituent at the C2-position is the key to the remarkable stability of these open-shell species as it provides appropriate room for the spin-density delocalization. Two catalytic as well as high-yielding protocols have been developed to install a suitable aryl group at the C2-position of NHCs. The spin-density in mono-radicals (NHCAr)• is mostly located on the parent carbene carbon (C2) atom. The bridging of two NHCs through a phenylene spacer (C6 H4) n enables the isolation of various p -quinodimethane (p -QDM) derivatives, which may be considered as open-shell Kekulé diradicaloids. The diradical character of these NHC-analogues of Thiele (n = 1), Chichibabin (n = 2), and Müller (n = 3) hydrocarbons [(NHC)(C6 H4) n (NHC)] can be tuned by a rational choice of the size and/or the topology of spacers. In this account, the synthesis, structure, and properties of this new class of radical hydrocarbons is presented. 1 Introduction 2 NHC-Monoradicals 3 NHC-Diradicaloids 4 Conclusion [ABSTRACT FROM AUTHOR]

• Highly selective synthesis of disulfide bonds in the gas phase. • Covalent bond formation to identify sites of noncovalent crown ether binding. • Both biradical and diradical species can be used for bond synthesis. Photoinitiated radical chemistry has proven to be useful for breaking covalent bonds within many biomolecules in the gas phase. Herein, we demonstrate that radical chemistry is useful for bond synthesis in the gas phase. Single peptides containing two cysteine residues capped with propylmercaptan (PM) often form disulfide bonds following ultraviolet excitation at 266 nm and loss of both PM groups. Similarly, noncovalently bound peptide pairs where each peptide contains a single cysteine residue can be induced to form disulfide bonds. Comparison with disulfide bound species sampled directly from solution yields identical collisional activation spectra, suggesting that native disulfide bonds have been recapitulated in the gas phase syntheses. Another approach utilizing radical chemistry for covalent bond synthesis involves creation of a reactive diradical that can first abstract hydrogen from a target peptide, creating a new radical site, and then recombine the second radical with the new radical to form a covalent bond. This chemistry is illustrated with 2-(hydroxymethyl-3,5-diiodobenzoate)-18-crown-6 ether, which attaches noncovalently to protonated primary amines in peptides and proteins. Following photoactivation and crosslinking, the site of noncovalent adduct attachment can frequently be determined. The ramifications of these observations on peptide structure and noncovalent attachment of 18-crown-6-based molecules is discussed. [ABSTRACT FROM AUTHOR]

Mesoionics are neutral compounds that cannot be represented by a fully covalent or purely ionic structure. Among the possible mesomeric structures of these compounds are the diradical electronic configurations. Theoretical and experimental studies indicate that some mesoionic rings are unstable, which may be related to a significant diradical character, that until then is not quantified. In this work, we investigated the diradical character of four heterocycles: 1,3-oxazol-5-one, 1,3-oxazol-5-thione, 1,3-thiazole-5-one, and 1,3-thiazole-5-thione. The oxazoles are known to be significatively less stable than thiazoles. DFT and ab initio single (B3LYP, MP2, CCSD, and QCISD) and ab initio multi-reference (MR-CISD) methods with three basis sets (6-311+G(d), aug-cc-pVDZ, and aug-cc-pVTZ) were employed to assess the diradical character of the investigated systems, in gas phase and DMSO solvent, from three criteria: (i) HOMO-LUMO energy gap, (ii) determination of energy difference between singlet and triplet wave functions, and (iii) quantification of the most significant diradical character (y0, determined in the unrestricted formalism). All of the results showed that the diradical character of the investigated systems is very small. However, the calculated electronic structures made it possible to identify the possible origin of the oxazoles instability, which can help the design of mesoionic systems with the desired properties.

CarH is a cobalamin-based photoreceptor which has attracted significant interest due to its complex mechanism involving its organometallic coenzyme-B 12 chromophore. While several experimental and computational studies have sought to understand CarH's mechanism of action, there are still many aspects of the mechanism which remain unclear. While light is needed to activate the Co-C 5′ bond, it is not entirely clear whether reaction pathway involves singlet or triplet diradical states. A recent experimental study implicated triplet pathway and importance of intersystem crossing (ISC) as a viable mechanistic route for photoproduct formation in CarH. Herein, a combined quantum mechanics/molecular mechanics approach (QM/MM) was used to explore the involvement of triplet states in CarH. Two possibilities were explored. The first possibility involved photo-induced homolytic cleavage of the Co-C 5′ where the radical pair (RP) would deactivate to a triplet state (T 0) on the ground state potential energy surface (PES). However, a pathway for the formation of the photoproduct, 4′,5′-anhydroadenosine (anhAdo), on the triplet ground state PES was not energetically feasible. The second possibility involved exploring a manifold of low-lying triplet excited states computed using TD-DFT within the QM/MM framework. Viable crossings of triplet excited states with singlet excited states were identified using semiclassical Landau-Zener theory and the effectiveness of spin-orbit coupling by El-Sayed rules. Several candidates along both the Co-N Im potential energy curve (PEC) and Co-C 5′ /Co-N Im PES were identified, which appear to corroborate experimental findings and implicate the possible role of triplet states in CarH. [Display omitted] • QM/MM calculations employed to explore the role of triplet states in photoreceptor CarH. • Excited state deactivation mechanism involving a triplet diradical was explored. • Manifold of low-lying triplet excited states in CarH computed using TD-DFT. • Landau-Zener theory and El-Sayed rules were used to estimate effective spin-orbit coupling. • Multiple triplet states identified as potential candidates for intersystem crossing in CarH. [ABSTRACT FROM AUTHOR]

The mechanism of the thermal cyclization of enyne-carbodiimides 7a–c has been studied computationally by applying the DFT method. The results indicate that enyne-carbodiimides preferentially follow the C2–C6 (Schmittel) cyclization pathway in a concerted fashion although the Myers–Saito diradical formation is kinetically preferred. The experimentally verified preference of the C2–C6 over the Myers–Saito pathway is guided by the inability of the Myers–Saito diradical to kinetically compete in the rate-determining trapping reactions, either inter- or intramolecular, with the concerted C2–C6 cyclization. As demonstrated with enyne-carbodiimide 11, the Myers–Saito channel can be made the preferred pathway if the trapping reaction by hydrogen transfer is no more rate determining.

Conjugated polymer nanoparticles (CP NPs) that could absorb the first near-infrared (NIR-I) window have emerged as highly desirable therapeutic nanomaterials. Here, a quinoidal-conjugated polymer (QCP), termed PQ, was developed as a novel class of therapeutic agents for photothermal therapy (PTT). Owing to its intrinsic quinoid structure, PQ exhibits molecular planarity and π-electron overlap along the conjugated backbone, endowing it with a narrow band gap, NIR-I absorption, and diradical features. The obtained PQ was coated with a poly(ethylene glycol) (PEG) moiety, affording nanosized and water-dispersed PQ nanoparticles (PQ NPs), which consequently show a high photothermal conversion efficiency (PCE) of 63.2%, good photostability, and apparent therapeutic efficacy for both in vitro and in vivo PTTs under an 808 nm laser irradiation. This study demonstrates that QCPs are promising active agents for noninvasive anticancer therapy using NIR-I light.

The electronic structure of biradicals is characterized by the presence of two unpaired electrons in degenerate or near-degenerate molecular orbitals. In particular, some of the most relevant species are highly reactive, difficult to generate cleanly and can only be studied in the gas phase or in matrices. Unveiling their electronic structure is, however, of paramount interest to understand their chemistry. Photoelectron photoion coincidence (PEPICO) spectroscopy is an excellent approach to explore the electronic states of biradicals, because it enables a direct correlation between the detected ions and electrons. This permits to extract unique vibrationally resolved photoion mass-selected threshold photoelectron spectra (ms-TPES) to obtain insight in the electronic structure of both the neutral and the cation. In this review we highlight most recent advances on the spectroscopy of biradicals and biradicaloids, utilizing PEPICO spectroscopy and vacuum ultraviolet (VUV) synchrotron radiation., (© 2023 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

Abstract: The magnetic behavior of the fluorene bridged verdazyl diradicals has been studied theoretically in their neutral and deprotonated states. The deprotonation of C9‐H site of the fluorene ring opens a new coupling pathway, which changes the nature of magnetic coupling. The transmission spectra analysis reveals that the transmission through fluorine has also increased due to the opening of a new coupling path after deprotonation. [ABSTRACT FROM AUTHOR]