Systematically Studying the Effect of Fluoride on the Properties of Cyclophanes Bearing Naphthalene Diimide and Dialkoxyaryl Groups

Young, Nicholas A.; Drew, Simon C.; Maniam, Subashani; Langford, Steven J.

doi:10.1002/asia.201700459

Cited by 11 publications

(12 citation statements)

References 35 publications

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“…Although ET from dithionite, carboxylate, and iodide anions has been long known, − that from a strong Lewis basic anion, F – was deemed counterintuitive based on a common misperception that F – was such a strong electronegative species that it could not donate an electron. Yet, study after study − unequivocally showed that in aprotic environments where anions are not solvent-stabilized, highly Lewis basic F – , OH – , and CN – anions routinely reduced various π-acids (Figure ) to paramagnetic πA •– radical anions and sometimes to πA 2– dianions, whereas the less Lewis basic halides failed to do so. Although these observations were at odds with the common perception, they actually shined a bright spotlight on an obvious but oft-overlooked fact: while neutral fluorine atoms with a zero formal charge are electronegative, the free F – anion is not, because it can no longer accept or accommodate another electron.…”

Section: Introductionmentioning

confidence: 99%

“…The renaissance of anion-induced ET (AIET) began earnestly in 2010 when (i) we first recognized formal ET from F – to a π-acidic naphthalenediimide (NDI) compound in various aprotic solvents (DMF, DMSO, and MeCN) leading to the formation of a paramagnetic NDI •– radical anion and an NDI 2– dianion, (ii) Bucher observed F – -induced reduction of methyl viologen (MV 2+ ) to MV •+ , (iii) Mukhopadhyay reported ET from CN – to NDI and perylenediimide (PDI) compounds, and (iv) Matile noticed ET from I – to a highly π-acidic dicyano-NDI (DCNDI) compound, but speculated that F – perhaps formed a Meisenheimer complex via nucleophilic attack instead of ET. Subsequently, a flurry of investigations − revealed that other π-acids, such as 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (HAT(CN) 6 ), tetracyanoquinodimethane (TCNQ), C 60 , [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM), PTANTT, an n-type conjugated polymer, and a Lewis acid Ag + (Figure )practically any electron acceptor with a LUMO level of −3.8 eV or less or a reduction potential of −900 mV or less vs Ag/AgClwere consistently reduced by F – and other Lewis basic anions in various aprotic solvents as well as in solid films. The reduced forms of π-acids and Lewis acids display fascinating optical, electrical, and magnetic properties, which have been exploited for colorimetric and fluorimetric anion sensing, light-harvesting, improving electrical conductivity, and luminescent silver nanoparticle synthesis, among other applications.…”

Section: Introductionmentioning

confidence: 99%

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Anion-Induced Electron Transfer

Saha

2018

Acc. Chem. Res.

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As counterintuitive as it might seem, in aprotic media, electron transfer (ET) from strong Lewis basic anions, particularly F, OH, and CN, to certain π-acids (πA) is not only spectroscopically evident from the formation of paramagnetic πA radical anions and πA dianions, but also thermodynamically justified because these anions' highest occupied molecular orbitals (HOMOs) lie above the π-acids' lowest unoccupied molecular orbitals (LUMOs) creating negative free energy changes (Δ G° < 0). Depending on the relative HOMO and LUMO energies of participating anions and π-acids, respectively, the anion-induced ET (AIET) events take place either in the ground state or upon photosensitization of the π-acids. The mild basic and charge-diffuse anions with lower HOMO levels fail to trigger ET, but they often form charge transfer (CT) and anion-π complexes. Owing to their high HOMO levels in aprotic environments, strong Lewis basic anions, such as F enjoy much greater ET driving force (Δ G°) than mild and non-basic anions, such as iodide. In protic solvents, however, the former become more solvated and stabilized and lose their electron donating ability more than the latter, creating an illusion that F is a poor electron donor due to the high electronegativity of fluorine. However, UV-vis, EPR, and NMR studies consistently show that in aprotic environments, F reduces essentially any π-acid with LUMO levels of -3.8 eV or less, revealing that contrary to a common perception, the electron donating ability of F anion is not dictated by the electronegativity of fluorine atom but is a true reflection of high Lewis basicity of the anion itself. Thus, the neutral fluorine atoms with zero formal charge and F anion have little in common when it comes to their electronic properties. The F anion can also legitimately act as a Brønsted base when the proton source has a p K lower than that of its conjugate acid HF (15), not the other way around, and ET from F to a poor electron acceptor is not thermodynamically feasible. While there is no shortage of indisputable evidence and clear-cut thermodynamic justifications for ET from F and other Lewis basic anions to various π-acids in aprotic solvents, because of the aforesaid misconception, it had been posited that F perhaps formed diamagnetic Meisenheimer complexes via nucleophilic attack, deprotonated an aprotic solvent DMSO against an insurmountably high p K (35) leading to a π-acid reduction, or formed [F/πA] complexes via a thermodynamically prohibited oxidation of π-acids. Unlike AIET, however, none of these hypotheses was thermodynamically viable nor supported by any experimental evidence. First, by defining the thermodynamic criteria of AIET pathways and all other alternate hypotheses and then evaluating the spectroscopic signals emanating from the interactions between different anions and π-acids and Lewis acids in the light of these criteria, this Account comes to a conclusion that AIET is the only viable mechanism that can rationalize the reduction of π-acids without violating any ther...

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Anion-Induced Electron Transfer

Saha

2018

Acc. Chem. Res.

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“…Among various noncovalent interactions, − anion−π interaction, i.e., the interaction between the anion and an electron deficient organic π-system with a strong positive quadruple moment, − has attracted considerable attention in supramolecular chemistry. − Several research groups are actively involved in exploring anion−π interaction in solution as well as in solid state along with computational support. − Among the anion/π complexes, reported to date, only a few are able to perturb the electronic properties of the π-acceptors. − Naphthalene tetra carboxylic diimide (NDI) units having a very large positive quadruple moment are important in this regard. Saha and co-workers have reported that the interaction of NDI with fluoride involves an electron transfer process in which NDI is reduced to the corresponding radical anion and sometimes dianion depending upon the electron donating ability of the anion and the π-acidity of the acceptor. − Some recent reports have opposed this direct electron transfer and have suggested that electron transfer likely took place via deprotonated solvents, formed by the anions in the medium. , The role of F – should therefore be investigated thoroughly because of the wide use of F – in sensing studies based on anion−π interaction and consequent charge transfer (CT) or electron transfer (ET).…”

Section: Introductionmentioning

confidence: 99%

“…Saha and co-workers have reported that the interaction of NDI with fluoride involves an electron transfer process in which NDI is reduced to the corresponding radical anion and sometimes dianion depending upon the electron donating ability of the anion and the π-acidity of the acceptor. − Some recent reports have opposed this direct electron transfer and have suggested that electron transfer likely took place via deprotonated solvents, formed by the anions in the medium. , The role of F – should therefore be investigated thoroughly because of the wide use of F – in sensing studies based on anion−π interaction and consequent charge transfer (CT) or electron transfer (ET). All of these reports on fluoride sensing based on the NDI platform utilizing anion−π and the electron transfer process dealt with mainly UV–vis and colorimetric methods. − As luminescence detection is a much more sensitive technique over UV–vis and colorimetric methods, herein, we describe a new dinuclear bis-heteroleptic Ru(II) complex of 1,10-phenanthroline and pyridine triazole hybrid ligand attached to a π-deficient NDI unit (Chart ) exhibiting fluoride sensing via luminescence “OFF–ON” at the Ru(II) center along with the sensing through UV–vis and colorimetric methods. Furthermore, we show that this triad can differentiate cyanide and fluoride with a different output.…”

Section: Introductionmentioning

confidence: 99%

Discriminative Behavior of a Donor–Acceptor–Donor Triad toward Cyanide and Fluoride: Insights into the Mechanism of Naphthalene Diimide Reduction by Cyanide and Fluoride

et al. 2020

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A new molecular donor−acceptor−donor (D−A−D) triad, comprised of an electron deficient 1,4,5,8-naphthalene tetracarboxylic diimide (NDI) unit covalently connected to two flanking photosensitizers, i.e., a bis-heteroleptic Ru(II) complex of 1,10-phenanthroline and pyridine triazole hybrid ligand, is described. The single crystal X-ray structure of the perchlorate salt of the triad demonstrates that the electron deficient NDI unit can act as a host for anions via anion−π interaction. Detailed solutionstate studies indicate that fluoride selectively interacts with the D−A−D triad to form a dianionic NDI, NDI 2− , via a radical anion, NDI •− . On the contrary, cyanide reduces the NDI moiety to NDI •− , as confirmed by UV− vis, NMR, and EPR spectroscopy. Further, femtosecond transient absorption spectroscopic studies reveal a low luminescence quantum yield of the D−A−D triad attributable to the photoinduced electron transfer (PET) process from the photoactive Ru(II) center to the NDI unit. Interestingly, the triad displays "OFF−ON" luminescence behavior in the presence of fluoride by restoring the Ru(II) to phenanthroline/pyridine-triazole-based MLCT emission, whereas cyanide fails to show a similar property due to a different redox process operational in the latter. The reduction of NDI in the presence of fluoride and cyanide in different polar solvents indicates that involvement of such deprotonated solvents in the electron transfer mechanism may not be operative in our present system. Lowtemperature kinetic studies support the formation of a charge transfer associative transient species, which likely allows overcoming the thermodynamically uphill barrier for the direct electron transfer mechanism.

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“…[17] NDI also perform electrochemical redox due to its electron deficient aromatic ring which leads to its application as sensors for detection of anions in solution. [18] We have extensively investigated organic redox polymer-based rechargeable devices and have shown that phthalimide and pyromellitic polyimides formed on carbon nanofibers are capable to perform as electrode-active material. [19] NDIs have been incorporated in polymers as part of the backbone to introduce rigidity, increase electron mobility, and thermal stability.…”

Section: Introductionmentioning

confidence: 99%