Electron-deficient Naphthalene Diimide Research Articles

Photochromic and photocontrolled luminescence properties of two metal-organic frameworks constructed from a naphthalene diimide derivative

Naphthalene diimides (NDIs), a class of organic dyes with high photochemical activity and strong luminescent characteristics, have attracted considerable interest because of their photoinduced electron transfer to form stable radical anions in the presence of electron donors upon irradiation. In this paper, two novel metal–organic frameworks constructed from NDIs chromophoric and aromatic dicarboxylic acids, [Zn2(DPMNI)(NCA)2·0.5DMF] (1), [Zn(DPMNI)(PTA)·DMF] (2), (H2NCA = 1,4-naphthalenedicarboxylic acid, H2PTA = p-phthalic acid, DPMNI = N,N′-bis(4-pyridylmethyl)-1,4,5,8-naphthalene diimide, DMF = N,N′-dimethylformamide), have been synthesized and characterized systematically. Because of the presence of electron-deficient NDI moieties, they exhibit reversible naked photochromic properties upon irradiation and photocontrolled luminescence due to the generation of NDI radicals. The carboxylate groups as electron donors play a key role in the photoinduced electron-transfer process, and the lone pair–π interaction is a preferred pathway to support photoinduced electron transfer from our work. This study has not only convincingly corroborated the relationship between the photoresponsive rate and non-covalent interactions, but also provided a feasible idea to design novel luminescence switching materials.

A series of V-shaped small molecule non-fullerene electron acceptors for efficient bulk-heterojunction devices

Two simple semiconducting acceptor-acceptor1-donor-acceptor (A-A1-D-A) modular, small molecule non-fullerene electron acceptors, 2-(4-(7-hexadecyl-1,3,6,8-tetraoxo-3,6,7,8-tetrahydrobenzo[lmn][3,8]phenanthrolin-2(1H)-yl)phenyl)-3-(6-((4-(7-hexadecyl-1,3,6,8-tetraoxo-3,6,7,8-tetrahydrobenzo[lmn][3,8]phenanthrolin-2(1H)-yl)phenyl)ethynyl)-9-octyl-9H-carbazol-3-yl)buta-1,3-diene-1,1,4,4-tetracarbonitrile (NDICz-5) and 2-(4-(3,3-dicyano-2-(4-(7-hexadecyl-1,3,6,8-tetraoxo-3,6,7,8-tetrahydrobenzo[lmn][3,8]phenanthrolin-2(1H)-yl)phenyl)-1-(6-((4-(7-hexadecyl-1,3,6,8-tetraoxo-3,6,7,8-tetrahydrobenzo[lmn][3,8]phenanthrolin-2(1H)-yl)phenyl)ethynyl)-9-octyl-9H-carbazol-3-yl)allylidene)cyclohexa-2,5-dien-1-ylidene)malononitrile (NDICz-6), were designed, synthesized and characterized for application in solution-processable bulk-heterojunction solar cells. The optoelectronic and photovoltaic properties of NDICz-5 and NDICz-6 were directly compared with those of a structural analogue, 7,7'-(((9-octyl-9H-carbazole-3,6-diyl)bis(ethyne-2,1-diyl))bis(4,1-phenylene))bis(2-hexadecylbenzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone) (NDICz-4), which was designed based on an A-D-A format. All of these new materials were designed to be V-shaped and comprised an electron rich carbazole donor core (D) together with electron deficient naphthalene diimide terminal core (A). In the simple A-D-A system, naphthalene diimide was the terminal functionality, whereas in the A-A1-D-A system, tetracyanoethylene (TCNE) and tetracyanoquinodimethane (TCNQ) derived functionalities were incorporated as A1 units by keeping D/A units constant. The inclusion of A1 was mainly done to induce cross-conjugation within the molecular backbone and hence to improve light-harvesting. The physical and optoelectronic properties were characterized by ultraviolet–visible, thermogravimetric analysis, photo-electron spectroscopy in air and cyclic voltammetry. These new materials exhibited energy levels complementing those of the conventional donor polymer poly(3-hexyl thiophene) (P3HT). Solution-processable bulk-heterojunction devices were fabricated with NDICz-4, NDICz-5 and NDICz-6 as non-fullerene electron acceptors. Studies on the photovoltaic properties revealed that the best P3HT: NDI-Cz6-based device showed an impressive enhanced power conversion efficiency of 7.58%, an increase of around two-fold with respect to as-cast blend, after solvent vapor annealing using carbon disulfide. Not only are the results among the best in the current literature using the conventional donor polymer P3HT, but clearly demonstrate that A-A1-D-A type, V-shaped small molecules are promising non-fullerene acceptors in the research field of organic solar cells.

Switchable luminescent properties in two photochromic naphthalene diimide coordination networks

Photochromic materials as a new class of multifunctional materials have received much attention owing to their potential applications in many fields. In order to investigate the electron-transfer photochromic behaviour of coordination polymers, two new coordination polymers based on the electron-deficient naphthalene diimide (NDI) and dicarboxylate ligand, namely [Zn2(DPNDI)(TPDC)2] (1) [Cd6(DPNDI)(TPDC)6(DMF)6] (2) (DPNDI = N,N′-di(3-pyridyl)-1,4,5,8-naphthalene tetracarboxydiimide, H2TPDC = thiophene-2,5-dicarboxylic acid, DMF = N,N′-dimethylformamide), were synthesized under solvothermal condition and were characterized by elemental analysis, IR spectroscopy, thermogravimetric analyses, and single-crystal X-ray diffraction. Complex 1 is a three-dimensional coordination with rhombus channels, whereas complex 2 shows a sandwiched layer structure. Because of the presence of electron-deficient NDI moieties, complexes 1 and 2 can easily undergo photoinduced electron transfer and eye-detectable photochromic behaviour. Moreover, their luminescence can be switched by UV–Vis light irradiation and standing in the air.

Dicyanodistyrylbenzene-Based Copolymers for Ambipolar Organic Field-Effect Transistors with Well-Balanced Hole and Electron Mobilities

We report three types of dicyanodistyrylbenzene (DCS)-based copolymers (PBDT-DCS, PT-DCS, and PNDI-DCS), which present highly balanced ambipolar charge transport characteristics in organic field-effect transistors (OFETs). The introduction of the DCS moiety in a polymer backbone not only lowers the lowest unoccupied molecular orbital (LUMO) level but also increases the crystalline ordering via interchain dipole–dipole interactions. As a result, the LUMO levels for PBDT-DCS, PT-DCS, and PNDI-DCS were decreased to −3.76, −4.00, and −3.99 eV, respectively, which is beneficial for efficient electron injection from Au electrode for improving ambipolar charge transport. The determined hole/electron mobilities of the OFETs were 0.064/0.014, 0.492/0.181, and 0.420/0.447 cm2/(V s) for PBDT-DCS, PT-DCS, and PNDI-DCS, respectively, after thermal annealing at 250 °C. By incorporating the electron-deficient naphthalene diimide (NDI) unit in the copolymers, the n-channel transport was enhanced, with decreasing frontier...

Core-insertion of palladium in naphthalenediimides: Opto-electronic properties, structural insights and coupling studies

Synthesis and isolation of palladium inserted functional π-scaffold is considered a major challenge due to its high instability and reactivity towards molecular oxygen. Herein, we report two σ-bonded compounds (1 and 2) between Naphthalenediimide (NDI) and palladium triphenylphosphine. Both these core-substituted NDI-palladium compounds have been characterized as NDI-{Pd(PPh3)2Br}2 having two Pd(PPh3)2 (1) and (C3H7)NH-NDI-Pd(PPh3)2Br having one Pd(PPh3)2 and n-propylamine as a donor moiety (2). Both the NDI-Pd compounds have been prepared by oxidative addition of Pd(0) triphenylphosphine with their respective core-brominated NDI having axially substituted n-hexyl groups. Interestingly, both these compounds showed remarkable stability towards column chromatography. Syntheses of 1 and 2 have been well characterised by different spectroscopic and analytical techniques. Cyclic voltammetry experiments were performed to understand the redox properties of the isolated NDI-Pd compounds. The structures of 1 and 2 have been crystallographically characterised. Solid state packing of both the compounds display strong intramolecular π-π stacking interactions between the electron-deficient NDI scaffold and the phenyl rings of the PPh3 unit(s). Moreover, both 1 and 2 exhibits interesting self-assembled architectures via intermolecular hydrogen and halogen bonding. Theoretical calculations were performed to evaluate frontier molecular orbitals and the intramolecular interactions. Furthermore, compound 1 was further utilized for the synthesis of Suzuki coupled bis-cyanophenyl compound in high yield.

High-Yielding Synthesis of Chiral Donor–Acceptor Catenanes

We report the synthesis of [2]catenanes (Hopf links) in water utilizing disulfides and aromatic donor-acceptor interactions. The electron-rich dialkoxynaphthalene (DN) building blocks interact with electron-deficient naphthalenediimide (NDI) moieties connected by a polyamine chain. We study the effect of the polyamine linkers on the behavior of the library. The polyamine's length and the number of nitrogen atoms in the chain affect the library distribution, leading in some cases to the assembly of catenanes in up to 93% yield.

Synthesis and properties of functional dyes with squaraine–naphthalene diimide hybrid structure

Naphthalene diimides (NDIs) are promising candidate for electron acceptors due to their low-lying HOMOs and LUMOs. The functinalization of soluble NDIs at the 2,6-position affects the absorption and electrochemical properties. In this study, NDI-based hybrid dyes NDI-SQ-A, B fused with squaraine chromophore were designed and synthesized in order to elucidate the effects of the substitution on their optical and electrochemical properties. These dyes were successfully synthesized by Stille coupling reactions using 3-stannylcyclobutenediones and brominated NDI derivative, followed by a condensation reaction. DFT calculation predicts that the present dyes adopt distorted structures coming from a steric hindrance between semisquaraine and NDI moieties. The hybrid dyes show low-lying LUMOs due to the introduction of electron-deficient NDI moiety and broad absorption spectra in the far-red region. The absorption spectra of their thin films were bathochromically shifted relative to those in solution, indicating that hybrid dyes formed J aggregates.

Lowering Band Gap of an Electroactive Metal-Organic Framework via Complementary Guest Intercalation.

A new honeycomb-shaped electroactive metal-organic framework (MOF) has been constructed from an electron deficient naphthalenediimide (NDI) ligand equipped with two terminal salicylic acid groups. π-Intercalation of electron-rich planar tetrathiafulvalene (TTF) guests between the NDI ligands stacked along the walls lowers the electronic band gap of the material by ca. 1 eV. An improved electron delocalization through the guest-mediated π-donor/acceptor stacks is attributed to the diminished band gap of the doped material, which forecasts an improved electrical conductivity.

Liquid-Assisted One-Pot Mechanosynthesis and Properties of Neutral Donor-Acceptor [2]Rotaxanes.

An efficient liquid-assisted one-pot two-step synthesis of neutral donor-acceptor [2]rotaxanes has been successfully realized under high-speed vibration milling conditions, by taking advantage of the donor-acceptor interaction between the electron-rich naphthalene unit of a macrocyclic polyether and the electron-deficient naphthalene diimide unit of a thread component for the threading process and click reaction as the stoppering process. The present method provides a powerful, fast, and environmentally benign alternative to traditional solvent-based approaches due to its notable advantages such as very small amount of solvent, no external heating, shorter reaction time, and higher yield. In addition, the charge-transfer interaction and electrochemically induced shuttling of the synthesized neutral donor-acceptor [2]rotaxanes have been demonstrated.

The catassembled generation of naphthalene diimide coordination networks with lone pair-π interactions

Catassembly is a new concept in molecular assembly that is analogous to catalysis in chemical synthesis. However, for most molecular-assembled processes, the catassembler contributions are rather inconspicuous due to the low activation barriers. As a result, few systems dealing with the catassembly are available until now. In this paper, we report that naphthalene diimide coordination networks are formed under the catassembly of lone-pair-bearing catassemblers (e.g., N,N-dimethylacetamide, N-methylpyrrolidin-2-one). During such molecular assembly, a stable transition state between the electron-deficient naphthalene diimide tectons and catassemblers via the less common lone pair-π interactions was observed, which is supposed to play the key role in the enhancement of coordination abilities of organic tectons and thus formation of the final coordination networks.

Design, Synthesis and Evaluation of Bifunctional Acridinine-Naphthalenediimide Redox-Active Conjugates as Antimalarials.

A novel class of bifunctional molecules was synthesized integrating acridine (Ac) and redox-active naphthalenediimide (NDI) scaffolds directly and through a flexible linker (en). We evaluated in vitro antiplasmodial activity, physicochemical properties, and a possible mode of action. Theoretical studies suggested electronic segmentation between the electron-rich Ac and electron-deficient NDI scaffolds. Orthogonal Ac–NDI molecules showed activities in the micromolar to submicromolar range against a chloroquine (CQ)-sensitive strain of human malaria pathogen Plasmodium falciparum (maximum activity, IC50: 0.419 μM). The flexible Ac–en–NDI molecules were most potent and showed activity in the nanomolar range against both CQ-sensitive (with most effective compounds, IC50: 3.65 and 4.33 nM) as well as CQ-resistant (with most effective compounds, IC50: 52.20 and 28.53 nM) strains of P. falciparum. Significantly, with CQ-resistant strains, the activity of the most effective compounds was 1 order of magnitude better than that of standard drug CQ. Ac–en–NDI-conjugated molecules were significantly more potent than the individual NDI and Ac-based molecules. The structure–activity relationship (SAR) suggests that the flexible spacer (en) linking the Ac and NDI scaffolds plays a vital role in exhibiting improved potency. None of the molecules triggered hemolysis in culture, and the most potent compounds did not show cytotoxicity in vitro against mammalian fibroblast NIH3T3 cells at their respective IC50 values. The other significant outcome of this work is that some of the investigated molecules have the potential to affect multiple processes in the parasite including the hemozoin formation in digestive vacuoles (DVs), mitochondrial membrane potential, and the redox homeostasis of the parasite.

Terpolymer approach for controlling the crystalline behavior of naphthalene diimide-based polymer acceptors and enhancing the performance of all-polymer solar cells

A new series of n-type D–A terpolymers (P(NDI2HD-T-S)) was synthesized from an electron-deficient naphthalene diimide (NDI)-based unit in conjugation with two electron-rich thiophene (T) and selenophene (S) units, and their performances as electron acceptors in all-polymer solar cells (all-PSCs) were compared. The crystallinity of the P(NDI2HD-T-S) terpolymers can be systematically controlled by tuning the T/S molar ratios (T/S=100/0, 80/20, 50/50, 20/80 and 0/100) in the polymer backbone. An increase in the S content induced a significant enhancement in the crystallinity of the terpolymers. Therefore, the incorporation of more S units enhanced the structural ordering of the terpolymers and the electron mobility in the all-PSCs. The power conversion efficiency of the all-PSCs based on a P(NDI2HD-T-S) terpolymer acceptor and a PTB7 polymer donor increased from 2.50 to 3.60% as the S content increased, which was primarily due to the enhanced short-circuit current. To understand the effects of the T/S compositions on the photovoltaic performances, we investigated their influence on the optical, electrical and structural properties of the n-type D–A terpolymers. A series of n-type D–A terpolymers (P(NDI2HD-T-S)) with various thiophene (T) and selenophene (S) compositions (T/S=100/0, 80/20, 50/50, 20/80 and 0/100) was successfully synthesized. To understand the effects of the T/S ratios, we studied their influence on the optical, electrical and structural properties. The insertion of more S content in the polymer backbone induced the enhanced structural ordering and electron mobility. Therefore, the all-polymer solar cells based on PTB7:P(NDI2HD-T-S) blend had greatly improved efficiency as the S content increased.

A NIR dye with high-performance n-type semiconducting properties.

A novel hetero-polycyclic aromatic compound manifesting strong near-infrared (NIR) absorption as well as high-performance n-type semiconducting properties is developed. With an exceptionally low LUMO level at -4.7 eV, this NIR dye (λmax ≈ 1100 nm, ε ≈ 105 mol-1 L cm-1) exhibits adequate stability under ambient conditions, with electron mobility up to 0.96 cm2 V-1 s-1 measured in solution-processed organic field-effect transistors. A special metal-free C-C coupling serves as a pivotal step in constructing the polycyclic π-framework of this low-bandgap chromophore, by fusing an electron-deficient naphthalenediimide moiety with an electron-donating naphthalenediamine. Such a rare combination of extraordinary optical and semiconductive attributes is quite valuable for organic small molecules, and promising for unique applications in the opto-electronic field.

Theoretical Strategy To Design Novel n-Type Copolymers Based on Anthracene Diimide and Pyrido[2,3-g]quinoline Diimide for Organic Solar Cells

The design and synthesis of efficient electron-transporting materials have been an active area of research in the area of organic solar cells (OSCs), organic field-effect transistors (OFETs), and organic light-emitting diodes (OLEDs). This paper is focused on designing novel n-type donor-acceptor (D-A) copolymers as electron-transporting materials for replacing the widely used fullerene acceptor materials in OSC applications. We first present a strategy which can remarkably improve the photovoltaic performances of D-A copolymer acceptors by means of adjusting the molecular planarity and intensifying the electron-withdrawing ability of electron-deficient units. Then we further analyze the role played by the D-A copolymer acceptor in the light-absorbing performance of the active layer. On the basis of two reported two D-A copolymer acceptors (PNDIT and P(NDI2OD-T2)) which are composed of an electron-deficient naphthalene diimide (NDI) unit and different electron-rich units of thiophene or bithiophene, replacement of the NDI unit with an anthracene diimide (ADI) unit and a pyrido[2,3-g]quinoline diimide (PQD) unit can produce two types of copolymer acceptors (P2, P3 and P2a, P3a). From the calculated results, the introduction of ADI and PQD units to replace the NDI unit can significantly improve the optoelectronic properties, light-absorbing efficiencies, and intermolecular electron transport abilities of the copolymers as well as exciton separation efficiencies at donor/acceptor interface. Finally, this study would give us a theoretical guidance to design efficient D-A copolymer acceptors for replacing fullerene acceptors in organic solar cells.

The impact of lone pair-π interactions on photochromic properties in 1-D naphthalene diimide coordination networks.

Lone pair-π interaction is an important but less studied binding force. Generally, it is too weak to influence the physical properties of supramolecular systems. Herein we reported the first example exhibiting the impact of lone pair-π interactions on photochromic properties of naphthalene diimide based coordination networks. In three isostructural 1-D networks, [(DPNDI)ZnX2] (DPNDI = N,N-di(4-pyridyl)-1,4,5,8-naphthalene diimide, X = Cl for 1, X = Br for 2 and X = I for 3), they exhibit different electron-transfer photochromic behaviors due to different lone pair-π interactions between the capped halogen atoms and electron-deficient DPNDI moieties. Specifically, 1 and 2 but not 3 are photochromic, which is attributed to a stronger lone pair-π interaction in 3 than those in 1 and 2. This study anticipates breaking a new path for designing novel photochromic materials through such unnoticeable supramolecular interactions.

Solid state organic amine detection in a photochromic porous metal organic framework.

A new Mg(ii) based photochromic porous metal-organic framework (MOF) has been synthesized bearing naphthalenediimide (NDI) chromophoric unit. This MOF (Mg-NDI) shows instant and reversible solvatochromic behavior in presence of solvents with different polarity. Mg-NDI also exhibits fast and reversible photochromism via radical formation. Due to the presence of electron deficient NDI moiety, this MOF exhibits selective organic amine (electron rich) sensing in solid state. The organic amine detection has been confirmed by photoluminescence quenching experiment and visual color change.

Controlled Polymerization of Electron-deficient Naphthalene-diimide Containing Monomer by Negishi-type Catalyst-transfer Polymerization

Negishi-type Catalyst-Transfer Polymerization (NCTP) of electron-deficient monomers has been attempted for the first time. Imide or ketone groups in such monomers show an excellent electron-deficient property. However, these functional groups cannot generally tolerate towad highly reactive Grignard reagents. In this work, we applied a zincate complex with lower basicity, tBu4ZnLi2, for the polymerization of a naphthalene-diimide-containing monomer. Zinc-halogen exchange reaction was quantitatively conducted at 60 °C for 1 h without any protection of the imide group. Then, the polymerization was carried out by adding the Pd catalyst to afford an electron-deficient polymer, PTNDIT (Mn = 8,400 and D = 1.35).

Lone pair–π interactions in naphthalene diimide π-acid dyes

The electron-deficient naphthalene diimides (NDIs) are ideal π-Lewis acid dyes for studies of lone pair–π interactions but remain unexplored. By a crystal engineering approach, herein we report that lone pair–π interactions between C = O and π-acceptors indeed have been found not only in free NDIs but also in their coordination networks. Interestingly, the lone pair–π interactions between C = O in the including solvents and NDIs are stronger than those found in the own C = O of imides, but weaker than the hydrogen-bonding interactions between solvent C = O and H-acceptors. In addition, the coordination by metal cation, the directionality and number of the lone-pair-bearing molecules play a crucial role on the lone-pair–π-interaction strength. These findings are undoubtedly of considerable significance for the development of NDI catalytic materials.

Understanding the Role of H-Bonding in Aqueous Self-Assembly of Two Naphthalene Diimide (NDI)-Conjugated Amphiphiles

Supramolecular architectures with the synchronized combination of various directional noncovalent forces are ubiquitous in biological systems. However, reports of such abiotic synthetic systems involving H-bonding in aqueous medium are rare due to the challenge faced in the formation of such structures by overcoming the competition from the water molecules. In this paper we have studied self-assembly of two structurally related naphthalene-diimide (NDI) conjugated bola-amphiphiles (NDI-1 and NDI-2) in water with an aim to realize the specific role of H-bonding among the hydrazide units present in one of the two building blocks (NDI-2) on the self-assembly. Both chromophores showed vesicular assembly in aqueous solution driven primarily by π-stacking among the NDI chromophores, which could be probed by UV-vis absorption spectra. Contrary to common belief, the lack of an H-bonding group in NDI-1 was found to be a boon in disguise in terms of the stability of the aggregates. Whereas NDI-2 aggregates showed LCST around 65-70 °C owing to the breaking of the H-bonds with increased temperature, the NDI-1 aggregates were found to be structurally intact until 90 °C, which may be attributed to the increased hydrophobicity introduced by the absence of the polar hydrazide group. Further concentration- and solvent-dependent UV-vis studies showed that NDI-1 formed assembled structure at greatly dilute solution and also in a solvent such as THF, confirming greater propensity for its self-assembly. As both bola-amphiphiles contain an electron-deficient NDI chromophore, interaction of their vesicles was studied with an externally added electron-rich pyrene derivative. Surprisingly, NDI-1 did not show any charge-transfer interaction with the donor, whereas NDI-2 could effectively intercalate, leading to a functional membrane with tunable surface functionalities. This was attributed to the additional stability of the intercalated state by H-bonding among the hydrazide units.

Electron-deficient naphthalene diimides as efficient planar π-acid organocatalysts for selective oxidative C–C coupling of 2,6-di-tert-butylphenol: A temperature effect

An efficient planar π-acid electron transfer organocatalyst based on electron-deficient substituted naphthalene diimide has been developed for oxidative C–C coupling of 2,6-di-tert-butylphenol to its dimeric derivative or unexpected ring-rearranged trimeric quinone methide by controlling the reaction temperatures.