Core-Modified Naphthalenediimides Generate Persistent Radical Anion and Cation: New Panchromatic NIR Probes

The generation of the first persistent radical cation of naphthalenediimide with Cu²⁺/Fe³⁺ under ambient conditions is reported. An alternate anionic trigger generates a persistent radical anion within the same motif. Steric protection and H-bonding enhances the half-life of radical cation by 290-fold. The radical anion and cation have orthogonal spin density, panchromatic and NIR optical bands, which can be applied as attractive multichannel probes

Extraordinary Stability of Naphthalenediimide Radical Ion and Its Ultra-Electron-Deficient Precursor: Strategic Role of the Phosphonium Group

Stabilization of radical ions and highly electron-deficient systems under ambient conditions is of great significance. A new design concept is presented that applies the multifaceted features of the phosphonium group to achieve isolation of (a) the first naphthalenediimide (NDI) radical ion [(<b>1a</b>^•+)­BPh₄^–] as single crystals and (b) an ultra-electron-deficient NDI [(<b>1a</b>²⁺)­2BF₄^–] having the lowest LUMO level recorded for an NDI, overwhelming the formative tetracyanoquinodimethane (<b>TCNQ</b>) molecule. Both <b>1a</b>^•+ and <b>1a</b>²⁺ exhibit unprecedented stability to normal workup procedures, chromatography, and anion metathesis in open air. To our knowledge, this is the first instance where radical ions stable toward chromatography have been obtained, which is a noteworthy development in the field of synthetic radical chemistry. The crucial components of thermodynamic and kinetic stabilization, namely, the nonbonded P···O interaction, hypervalency, and propeller-like shape of the phosphonium groups in <b>1a</b>²⁺ and <b>1a</b>^•+, were substantiated by crystallography and theoretical studies. Natural bond orbital (NBO) calculations validated the P···O contact to be an n_O → σ_P–C^* orbital interaction. Spontaneous electron transfer reactions of <b>1a</b>²⁺ even in nonpolar solvents, anion−π interactions of <b>1a</b>²⁺ with the naphthalene core, and panchromism of <b>1a</b>^•+ are the other emergent properties. The high-yielding (∼90%) in situ synthesis of <b>1a</b>^•+ and the extraordinary stability fostered by the phosphonium group have the potential to turn hitherto unstable organic systems into a new genre of stable <i>off-the-shelf</i> systems

Self-Assembly of an Organic Radical Thin Film and Its Memory Function Investigated Using a Liquid-Metal Electrode

In this work, the deposition of a persistent organic radical by thermal evaporation on Au, Pt, and graphene is performed. The impact of the deposition parameters and the nature of the substrate on the molecular organization within the deposited film are investigated. The nonplanarity of the molecule and the role of the molecule–molecule and molecule–substrate interactions are discussed. UV photoelectron spectroscopy experiments demonstrate that the radical character, and hence its magnetic and redox properties, is preserved on the three surfaces. The optimized films are electrically characterized by top-contacting the film/substrate system using a liquid metal that permits achievement of a soft contact avoiding damaging the layer. The hysteretic current versus voltage curves obtained from the electrical characterization point to the potential applicability of the studied system as an organic memory. Moreover, the demonstrated feasibility of using a liquid metal is an appealing approach toward the preparation of flexible devices

Toward Full Zigzag-Edged Nanographenes: <i>peri</i>-Tetracene and Its Corresponding Circumanthracene

Zigzag-edged nanographene with two rows of fused linear acenes, called as n-<i>peri</i>-acene (n-PA), is considered as a potential building unit in the arena of organic electronics. n-PAs with four (<i>peri</i>-tetracene, <b>4-PA</b>), five (<i>peri</i>-pentacene, <b>5-PA</b>) or more benzene rings in a row have been predicted to show open-shell character, which would be attractive for the development of unprecedented molecular spintronics. However, solution-based synthesis of open-shell n-PA has thus far not been successful because of the poor chemical stability. Herein we demonstrated the synthesis and characterization of the hitherto unknown <b>4-PA</b> by a rational strategy in which steric protection of the zigzag edges playing a pivotal role. The obtained <b>4-PA</b> possesses a singlet biradical character (<i>y</i>₀ = 72%) and exhibits remarkable persistent stability with a half-life time (<i>t</i>_1/2) of ∼3 h under ambient conditions. UV–vis–NIR and electrochemical measurements reveal a narrow optical/electrochemical energy gap (1.11 eV) for <b>4-PA</b>. Moreover, the bay regions of <b>4-PA</b> enable the efficient 2-fold Diels–Alder reaction, yielding a novel full zigzag-edged circumanthracene

Toward Full Zigzag-Edged Nanographenes: <i>peri</i>-Tetracene and Its Corresponding Circumanthracene

Zigzag-edged nanographene with two rows of fused linear acenes, called as n-<i>peri</i>-acene (n-PA), is considered as a potential building unit in the arena of organic electronics. n-PAs with four (<i>peri</i>-tetracene, <b>4-PA</b>), five (<i>peri</i>-pentacene, <b>5-PA</b>) or more benzene rings in a row have been predicted to show open-shell character, which would be attractive for the development of unprecedented molecular spintronics. However, solution-based synthesis of open-shell n-PA has thus far not been successful because of the poor chemical stability. Herein we demonstrated the synthesis and characterization of the hitherto unknown <b>4-PA</b> by a rational strategy in which steric protection of the zigzag edges playing a pivotal role. The obtained <b>4-PA</b> possesses a singlet biradical character (<i>y</i>₀ = 72%) and exhibits remarkable persistent stability with a half-life time (<i>t</i>_1/2) of ∼3 h under ambient conditions. UV–vis–NIR and electrochemical measurements reveal a narrow optical/electrochemical energy gap (1.11 eV) for <b>4-PA</b>. Moreover, the bay regions of <b>4-PA</b> enable the efficient 2-fold Diels–Alder reaction, yielding a novel full zigzag-edged circumanthracene

Toward Full Zigzag-Edged Nanographenes: <i>peri</i>-Tetracene and Its Corresponding Circumanthracene

Zigzag-edged nanographene with two rows of fused linear acenes, called as n-<i>peri</i>-acene (n-PA), is considered as a potential building unit in the arena of organic electronics. n-PAs with four (<i>peri</i>-tetracene, <b>4-PA</b>), five (<i>peri</i>-pentacene, <b>5-PA</b>) or more benzene rings in a row have been predicted to show open-shell character, which would be attractive for the development of unprecedented molecular spintronics. However, solution-based synthesis of open-shell n-PA has thus far not been successful because of the poor chemical stability. Herein we demonstrated the synthesis and characterization of the hitherto unknown <b>4-PA</b> by a rational strategy in which steric protection of the zigzag edges playing a pivotal role. The obtained <b>4-PA</b> possesses a singlet biradical character (<i>y</i>₀ = 72%) and exhibits remarkable persistent stability with a half-life time (<i>t</i>_1/2) of ∼3 h under ambient conditions. UV–vis–NIR and electrochemical measurements reveal a narrow optical/electrochemical energy gap (1.11 eV) for <b>4-PA</b>. Moreover, the bay regions of <b>4-PA</b> enable the efficient 2-fold Diels–Alder reaction, yielding a novel full zigzag-edged circumanthracene