Naphthalene Diimide Radical Anion Research Articles

High performance n-type thermoelectric material based on naphthalenediimide radical anions

An ideal organic thermoelectric (TE) material should possess features that would be low-cost, of high performance, easy to process, and non-toxic, but it is rare to find materials that meet these requirements. Naphthalenediimide (NDI), as a common and cheap industrial pigment, displays strong intermolecular inaction and good n-type semiconductor character. However, due to the strong interaction of π-π and hydrogen bond interaction, NDI usually exhibited poor solubility, making it difficult to process in solution. Herein, we demonstrated that the unsubstituted NDI could form a suspension mixed with NDI radical anion state by phenyl lithium doping, which consequently can be used to prepare dense film by drop-casting for TE application. More importantly, by optimizing the doping ratio, the TE film reached electrical conductivity of 0.11 S cm−1 and Seebeck coefficient of −1289 μV K−1. Eventually, a high power factor up to 18.8 μW m−1 K−2 and ZT value of 0.053 was obtained, which is one of the best TE performance achieved in n-type NDI-based TE materials. This work suggests the simple strategy of utilizing commercially mature molecules to develop organic TE materials with high performance.

Using Photoexcited Core/Shell Quantum Dots To Spin Polarize Appended Radical Qubits.

The synthetic tunability, flexibility, and rich spin physics of semiconductor quantum dots (QDs) make them promising candidates for quantum information science applications. However, the rapid spin relaxation observed in colloidal quantum dots limits their functionality. In the current work, we demonstrate a method to harness photoexcited spin states in QDs to produce long-lived spin polarization on an appended organic ligand molecule. We present a system composed of CdSe/CdS core/shell QDs, covalently linked to naphthalenediimide (NDI) electron-accepting molecules. The electron transfer dynamics from photoexcited QDs to the appended NDI ligands is explored as a function of both shell thickness and number of NDIs per QD. Transient EPR spectroscopy shows that the photoexcited QDs strongly spin polarize the NDI radical anion, which is interpreted in the context of both the radical pair and the triplet mechanisms of spin polarization. This work serves as an initial step toward using photoexcited QDs to strongly spin polarize organic radicals having long spin relaxation times to serve as spin qubits in quantum information science applications.

Photoexcited Naphthalene Diimide Radical Anion Linking the Nodes of a Metal–Organic Framework: A Heterogeneous Super-reductant

Photoexcited Naphthalene Diimide Radical Anion Linking the Nodes of a Metal–Organic Framework: A Heterogeneous Super-reductant

Electron Transfer from Photoexcited Naphthalene Diimide Radical Anion to Electrocatalytically Active Re(bpy)(CO)3Cl in a Molecular Triad

Electron donor–acceptor photosensitizers having long charge separation lifetimes and high-reducing potentials that can be easily appended to thermodynamically difficult to reduce catalysts hold great promise for driving CO2 reduction. This study presents a new molecular triad utilizing a naphthalene diimide radical anion (NDI•–) donor chromophore appended to a 9,10-diphenylanthracene (DPA) acceptor, which is in turn linked to Re(bpy)(CO)3Cl. The NDI•– chromophore is readily generated by mild chemical or electrochemical reduction, absorbs at wavelengths as long as 800 nm, and has an excited state oxidation potential (−2.1 V vs SCE), which rivals or exceeds those of metalorganic and organometallic chromophores. Photoexcitation of NDI•– to *NDI•– is followed by ultrafast reduction of DPA to DPA•–, which then rapidly reduces the metal complex. The overall quantum yield for reduction of Re(bpy)(CO)3Cl is approximately 90% using visible light. The overall time constant for the forward electron transfer to reduc...

On the Reaction of Naphthalene Diimides with Fluoride Ions: Acid/Base versus Redox Reactions

AbstractThe characterization of a naphthalene diimide (NDI) radical anion is presented. Its properties allow a reliable comparison point for other systems involving the NDI radical anion, such as systems claimed to perform the oxidation of the fluoride anion. In addition to reiterating the obvious thermodynamic objections to such an unlikely oxidation, we present several observations that show that the fluoride anion does not act as a one‐electron reducing agent toward the NDI investigated in this work.

On the Reaction of Naphthalene Diimides with Fluoride Ions: Acid/Base versus Redox Reactions.

The characterization of a naphthalene diimide (NDI) radical anion is presented. Its properties allow a reliable comparison point for other systems involving the NDI radical anion, such as systems claimed to perform the oxidation of the fluoride anion. In addition to reiterating the obvious thermodynamic objections to such an unlikely oxidation, we present several observations that show that the fluoride anion does not act as a one-electron reducing agent toward the NDI investigated in this work.

Photo-driven electron transfer from the highly reducing excited state of naphthalene diimide radical anion to a CO2 reduction catalyst within a molecular triad.

The naphthalene-1,4:5,8-bis(dicarboximide) radical anion (NDI-˙), which is easily produced by mild chemical or electrochemical reduction (-0.5 V vs. SCE), can be photoexcited at wavelengths as long as 785 nm, and has an excited state (NDI-˙*) oxidation potential of -2.1 V vs. SCE, making it a very attractive choice for artificial photosynthetic systems that require powerful photoreductants, such as CO2 reduction catalysts. However, once an electron is transferred from NDI-˙* to an acceptor directly bound to it, a combination of strong electronic coupling and favorable free energy change frequently make the back electron transfer rapid. To mitigate this effect, we have designed a molecular triad system comprising an NDI-˙ chromophoric donor, a 9,10-diphenylanthracene (DPA) intermediate acceptor, and a Re(dmb)(CO)3 carbon dioxide reduction catalyst, where dmb is 4,4'-dimethyl-2,2'-bipyridine, as the terminal acceptor. Photoexcitation of NDI-˙ to NDI-˙* is followed by ultrafast reduction of DPA to DPA-˙, which then rapidly reduces the metal complex. The overall time constant for the forward electron transfer to reduce the metal complex is τ = 20.8 ps, while the time constant for back-electron transfer is six orders of magnitude longer, τ = 43.4 μs. Achieving long-lived, highly reduced states of these metal complexes is a necessary condition for their use as catalysts. The extremely long lifetime of the reduced metal complex is attributed to careful tuning of the redox potentials of the chromophore and intermediate acceptor. The NDI-˙-DPA fragment presents many attractive features for incorporation into other photoinduced electron transfer assemblies directed at the long-lived photosensitization of difficult-to-reduce catalytic centers.

Photoredox-active Dyads Based on a Ru(II) Photosensitizer Equipped with Electron Donor or Acceptor Polymer Chains: A Spectroscopic Study of Light-Induced Processes toward Efficient Charge Separation

A photosensitizer–multielectron-acceptor dyad (P–An) was synthesized via controlled nitroxide-mediated polymerization of styrenic naphthalene diimide (NDI) and subsequent functionalization with a [Ru(dqp)2]2+ photosensitizer (dqp is 2,6-di(quinolin-8-yl)pyridine) at the chain terminus. The optical and electrochemical analysis showed the preserved properties of the individual subunits, corroborated by the analysis of the related multielectron donor assembly (Dn–P) based on triarylamine (TARA). A detailed photophysical study of both dyads is presented to elucidate the primary light-induced energy- and electron-transfer events. While the Dn–P dyad displays the unchanged 3MLCT-based (MLCT is metal-to-ligand charge transfer) emission of the pristine photosensitizer, the P–An system revealed efficient emission quenching and the occurrence of the NDI radical anion signature. The time-resolved emission data revealed a nonmonoexponential decay attributed to the conformational freedom by the flexible linkage, while the transient absorption data confirmed the rapid formation of the reduced acceptor.

Induction of Motion in a Synthetic Molecular Machine: Effect of Tuning the Driving Force

Rotaxane molecular shuttles were studied in which a tetralactam macrocyclic ring moves between a succinamide station and a second station in which the structure is varied. Station 2 in all cases is an aromatic imide, which is a poor hydrogen-bond acceptor in the neutral form, but a strong one when reduced with one or two electrons. When the charge density on the hydrogen-bond-accepting carbonyl groups in station 2 is reduced by changing a naphthalimide into a naphthalene diimide radical anion, the shuttling rate changes only slightly. When station 2 is a pyromellitimide radical anion, however, the shuttling rate is significantly reduced. This implies that the shuttling rate is not only determined by the initial unbinding of the ring from the first station, as previously supposed. An alternative reaction mechanism is proposed in which the ring binds to both stations in the transition state.

Photoinduced Electron Transfer in Zinc Naphthalocyanine-Naphthalenediimide Supramolecular Dyads

Photoinduced electron transfer was studied in self-assembled donor-acceptor dyads, formed by axial coordination of pyridine appended with naphthalenediimide (NDI) to zinc naphthalocyanine (ZnNc). The NDI-py:ZnNc (1) and NDI(CH(2))(2)-py:ZnNc (2) self-assembled dyads absorb light over a wide region of the UV/Vis/near infrared (NIR) spectrum. The formation constants of the dyads 1 and 2 in toluene were found to be 2.5×10(4) and 2.2×10(4) M(-1), respectively, from the steady-state absorption and emission measurements, suggesting moderately stable complex formation. Fluorescence quenching was observed upon the coordination of the pyridine-appended NDI to ZnNc in toluene. The energy-level diagram derived from electrochemical and optical data suggests that exergonic charge separation through the singlet state of ZnNc ((1)ZnNc*) provides the main quenching pathway. Clear evidence for charge separation from the singlet state of ZnNc to NDI was provided by femtosecond laser photolysis measurements of the characteristic absorption bands of the ZnNc radical cation in the NIR region at 960 nm and the NDI radical anion in the visible region. The rates of charge-separation of 1 and 2 were found to be 2.2×10(10) and 4.4×10(9) s(-1), respectively, indicating fast and efficient charge separation (CS). The rates of charge recombination (CR) and the lifetimes of the charge-separated states were found to be 8.50×10(8) s(-1) (1.2 ns) for 1 and 1.90×10(8) s(-1) (5.3 ns) for 2. These values indicate that the rates of the CS and CR processes decrease as the length of the spacer increases. Their absorption over a wide portion of the solar spectrum and the high ratio of the CS/CR rates suggests that the self-assembled NDI-py:ZnNc and NDI(CH(2))(2)-py:ZnNc dyads are useful as photosynthetic models.