Self-Assembly of Discrete Oligomers of Naphthalenediimides in Bulk and on Surfaces

Here, we report on the synthesis of discrete oligomers of alkyl-bridged naphthalenediimides (NDIs) and study their molecular nanostructures both in bulk, in solution, and at the liquid-solid interface. Via an iterative synthesis method, multiple NDI cores were bridged with short and saturated alkyl-diamines (C3 and C12 ) or long and unsaturated alkyl-diamines (u2 C33 to u8 C100 ) at their imide termini. The strong intermolecular interaction between the NDI cores was observed by probing their photophysical properties in solution. In bulk, the discrete NDI oligomers preferentially ordered in lamellar morphologies, irrespective of whether a saturated or unsaturated spacer was employed. Moreover, both the molecular architecture as well as the crystallization conditions play a significant role in the nanoscale ordering. The long unsaturated alkyl chains lead preferably to folded-chain conformations while their saturated analogues form stretched arrangements. At the solution-solid interface, well-defined lamellar regions were observed. These results show that precision in chemical structure alone is not sufficient to reach well-defined structures of discrete oligomers, but that it must be combined with precision in processing conditions.

Enhancing the Performance of Electret-Free Phototransistor Memory by Using All-Conjugated Block Copolymer

Conjugated polymers are of great interest owing to their potential in stretchable electronics to function under complex deformation conditions. To improve the performance of conjugated polymers, various structural designs have been proposed and these conjugated polymers are specially applied in exotic optoelectronics. In this work, a series of all-conjugated block copolymers (PII2T-b-PNDI2T) comprising poly(isoindigo-bithiophene) (PII2T) and poly(naphthalenediimide-bithiophene) (PNDI2T) are developed with varied compositions and applied to electret-free phototransistor memory. Accordingly, these memory devices present p-type transport capability and electrical-ON/photo-OFF memory behavior. The efficacy of the all-conjugated block copolymer design in improving the memory-photoresponse properties in phototransistor memory is revealed. By optimizing the composition of the block copolymer, the corresponding device achieves a wide memory window of 36 V and a high memory ratio of 7 × 10⁴ . Collectively, the results of this study indicate a new concept for designing electret-free phototransistor memory by using all-conjugated block copolymer heterojunctions to mitigate the phase separation of conjugated polymer blends. Meanwhile, the intrinsic optoelectronic properties of the constituent conjugated polymers can be well-maintained by using an all-conjugated block copolymer design.

Structural Transformable Coulomb Lattice of n-Type Semiconductors for Guest Sorption

In recent years, highly designable organic porous materials have attracted considerable attention in the development of new types of molecular adsorption-desorption materials. The adsorption-desorption process also changes the electronic structure via the existence of guest molecules. Therefore, it is possible to change the physical property during the guest adsorption-desorption cycle using an appropriate chemical design of the host crystal lattice. As the development of n-type organic semiconductors has been limited, we focused on designing an n-type organic semiconductor material to control the host crystal lattice, electronic dimensionality, chemical stability, and high electron mobility using an ionic naphthalenediimide (NDI) derivative. Low symmetrical dianionic bis(benzene-m-sulfonate)-naphthalenediimide (m-BSNDI^2-) forms various types of single-crystal (M⁺)₂(m-BSNDI^2-)·n(guest) with a combination of M⁺ = Na⁺, K⁺, Rb⁺, and guest = H₂O, CH₃OH. Four crystals of (K⁺)₂(m-BSNDI^2-)·n(H₂O), (K⁺)₂(m-BSNDI^2-)·n(CH₃OH), α-(K⁺)₂(m-BSNDI^2-), and β-(K⁺)₂(m-BSNDI^2-) were transformable using the guest adsorption-desorption cycle. Two kinds of single-crystal (K⁺)₂(m-BSNDI^2-)·n(CH₃OH) with n = 0 and 2.0 showed a single-crystal to single-crystal (SCSC) transformation through CH₃OH desorption. On the contrary, five kinds of single crystals with n = 0, 3.0, 3.3, 4.75, and 5.5 were identified in the single-crystal X-ray structural analyses of (K⁺)₂(m-BSNDI^2-)·n(H₂O). Systematic change of the ionic radii in (M⁺)₂(m-BSNDI^2-) modified the crystal lattice flexibility for the guest adsorption-desorption cycles.

A New 'Off-On' System Based on Core-Substituted Naphthalene Diimide with Dimethylamine for Reversible Acid-Base Sensing

A new 'Off-On' system designed and synthesised by functionalisation of a naphthalene diimide (NDI) core with dimethylamine produces 4,9-bis(dimethylamino)-2,7-dioctylbenzo[lmn][3,8]-phenanthroline-1,3,6,8-(2H,7H)-tetraone, abbreviated as DDPT (1). DDPT 1 was synthesised using a simple strategy, namely aromatic nucleophilic substitution using Br₂ -NDI with dimethylamine at 110 °C. DDPT was characterized by ¹ H and ¹³ C NMR spectroscopy, ESI mass spectrometry and elemental analysis. DDPT 1 was then used for optical studies through protonation of its dimethylamine core with trifluoroacetic acid (TFA), blue-shifting the absorption band from 600 nm to 545 nm in solution. Interestingly, the fluorescence of DDPT 1 is weak in solution with a quantum yield Φ=0.09, which is significantly enhanced to Φ=0.78 upon addition of TFA. The limit of detection (LOD) was determined to 2.77 nm. Furthermore, DDPT 1 can be used for naked eyed detection not only under UV light (365 nm) but also using visible light, as clear changes can be clearly seen upon addition of TFA. The binding constant of DDPT was calculated to 2.1×10^-3  m^-1 . Importantly, DDPT 1 showed reversible switching by alternative addition of acid (TFA) and base (triethylamine) without loss of activity. Immobilised on paper, DDPT 1 can be used for strip-test sensing in which the colour changes from blue to reddish when expose to TFA vapours and reverse in the presence of triethylamine vapours.

Immobilization of Ethynyl-π-Extended Electron Acceptors with Amino-Terminated SAMs by Catalyst-Free Click Reaction

Surface modification of SiO₂ using a catalyst-free quantitative reaction between an amine and an ethynyl-π-extended naphthalenediimide was investigated. A post-reaction method, in which the catalyst-free reaction was performed at the surface after the formation of amino-terminated self-assembled monolayers (SAMs), resulted in dense, uniform modification of the SiO₂ surface with the naphthalenediimide molecules. Both X-ray reflectivity and angle-resolved X-ray photoemission spectroscopy showed consistent results for the layer thickness and density. In contrast, a pre-reaction method, in which an amino-silane and the ethynyl-π-extended naphthalenediimide reacted first and then formed a SAM, afforded a sparse SAM on the SiO₂ surface, probably due to the steric hindrance of the naphthalenediimide moieties. The in situ decoration of the SiO₂ surface by a catalyst-free quantitative reaction offers a facile route for modifying surface properties with various π-conjugated molecules suitable for many applications.

Switching of Electron and Ion Conductions by Reversible H2O Sorption in n-Type Organic Semiconductors

Polar H₂O molecules generally act as trapping sites and suppress the electron mobility of n-type organic semiconductors, making chemical design of H₂O-tolerant and responsive n-type semiconductors an important step toward multifunctional electron-ion coupling devices. The introduction of effective electrostatic interactions between potassium ions (K⁺) and carboxylate (-COO^-) anions into the electron-transporting naphthalenediimide π-framework enables the design of high-performance H₂O-tolerant n-type semiconductors with a reversible H₂O adsorption-desorption ability, where the electron mobility and K⁺ ionic conductivity were coupled with the reversible H₂O sorption behavior. The reversible H₂O adsorption into the crystals enhanced the electron mobility from 0.04 to 0.28 cm² V^-1 s^-1, whereas the K⁺ ionic conductivity decreased from 3.4 × 10^-5 to 4.7 × 10^-7 S cm^-1. Because this reversible electron-ion conducting switch is responsive to H₂O sorption behavior, it is a strong candidate for H₂O gating carrier transport systems.

Diazapyrenes: interaction with nucleic acids and biological activity

The review summarizes data on the practical aspects of the interaction of nucleic acids with diazapyrene derivatives. The information on biological activity is given and the probable mechanisms underlying the action of diazapyrenes are analyzed. It contains 119 references.

Red-Emitting Delayed Fluorescence and Room Temperature Phosphorescence from Core-Substituted Naphthalene Diimides

Unprecedented ambient triplet-mediated emission in core-substituted naphthalene diimide (cNDI) derivatives is unveiled via delayed fluorescence and room temperature phosphorescence. Carbazole core-substituted cNDIs, with a donor-acceptor design, showed deep-red triplet emission in solution processable films with high quantum yield. This study, with detailed theoretical calculations and time-resolved emission experiments, enables new design insights into the triplet harvesting of cNDIs; an important family of molecules which has been, otherwise, extensively been investigated for its n-type electronic character and tunable singlet fluorescence.

Intersystem Crossing in Naphthalenediimide-Oxoverdazyl Dyads: Synthesis and Study of the Photophysical Properties

Oxoverdazyl (Vz) radical units were covalently linked to the naphthalenediimide (NDI) chromophore to study the effect of the radical on the photophysical properties, especially the radical enhanced intersystem crossing (REISC), which is a promising approach to develop heavy-atom-free triplet photosensitizers. Rigid phenyl or ethynylphenyl linkers between the two moieties were used, thus REISC and formation of doublet (D₁ , total spin quantum number S=1/2) and quartet states (Q₁ , S=3/2) are anticipated. The photophysical properties of the dyads were studied with steady-state and femtosecond/nanosecond transient absorption (TA) spectroscopies and DFT computations. Femtosecond transient absorption spectra show a fast electron transfer (<150 fs), and ISC (ca. 1.4-1.85 ps) is induced by charge recombination (CR, in toluene). Nanosecond transient absorption spectra demonstrated a biexponential decay of the triplet state of the NDI moiety. The fast component (lifetime: 50 ns; population ratio: 80 %) is assigned to the D₁ →D₀ decay, and the slow decay component (2.0 μs; 20 %) to the Q₁ →D₀ ISC. DFT computations indicated ferromagnetic interactions between the radical and chromophore (J=0.07-0.13 eV). Reversible formation of the radical anion of the NDI moiety by photoreduction of the radical-NDI dyads in the presence of sacrificial electron donor triethanolamine (TEOA) is achieved. This work is useful for design of new triplet photosensitizers based on the REISC effect.

Understanding of Fluorination Dependence on Electron Mobility and Stability of Naphthalenediimide-Based Polymer Transistors in Environment with 100% Relative Humidity

A family of copolymers (P(NDIOD-T2Fx)) based on naphthalenediimide (NDI) and 2,2'-bithiophene (T2) units with different amounts of 3,3'-difluoro-2,2'-bithiophene (T2F) decoration were synthesized, characterized, and used in n-type organic field-effect transistors (OFETs). With increasing T2F content in the backbone, we observe increased melting and crystallization transitions, blue-shifted absorptions, and deeper-lying highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) levels, together with improved hydrophobicity. The highest electron mobility of 4.48 × 10^-1 cm² V^-1 s^-1 was obtained for P(NDIOD-T2F0) without a T2F unit, which is attributed to the larger domain grains and crystallites, as well as a more tightly packed and oriented crystalline structure, as evidenced from the morphological study. In contrast, P(NDIOD-T2F100) with the highest T2F content has superior air stability, showing greater than 25% electron mobility retention after 30 days in wet conditions of 100% relative humidity without encapsulation. Even P(NDIOD-T2F100) is able to operate normally after 30 min of immersion in water, which is due to the synergistic contributions from the deep HOMO/LUMO levels and improved hydrophobicity. This study advances our fundamental understanding of how the morphology/crystallinity, device performance, and device stability of n-type copolymers are tuned by incorporating different concentrations of T2F in the backbone, shedding light on an important modification for air- and water-stable n-type materials for future OFET applications.

Four isostructural lanthanide(III) coordination compounds based on a new N-oxydic pyridyl naphthalenediimide ligand: synthesis and characterization

Naphthalenediimides, an attractive class of electron-deficient organic dyes with rich redox and photoredox properties, have been investigated extensively as building blocks for coordination networks or metal-organic frameworks in recent decades. However, most of the available work has focused on d-block metal cations rather than f-block lanthanide ions, whose complexes exhibit a large variability in coordination numbers. In this article, four coordination polymers composed of naphthalenediimides and lanthanide cations, namely catena-poly[[[tris(nitrato-κ²O,O')lanthanide]-bis{μ-N,N'-bis[(1-oxidopyridin-1-ium-3-yl)methyl]-1,8:4,5-naphthalenetetracarboxdiimide-κ²O:O'}-[tris(nitrato-κ²O,O')lanthanide]-μ-N,N'-bis[(1-oxidopyridin-1-ium-3-yl)methyl]-1,8:4,5-naphthalenetetracarboxdiimide-κ²O:O'] methanol disolvate], {[Ln(C₂₆H₁₆N₄O₄)_1.5(NO₃)₃]·CH₃OH}_n, with Ln = Eu, 1, Gd, 2, Dy, 3, and Er, 4, have been successfully synthesized under hydrothermal conditions. Single-crystal X-ray diffraction analyses revealed that the four compounds are isomorphic and that each asymmetric unit contains one nine-coordinated Ln centre, one and a half diimide ligands, three nitrate anions and one uncoordinated methanol molecule. In addition, each metal centre is surrounded by nine O atoms in a distorted tricapped trigonal-prismatic geometry. Two centres are bridged by two cis ligands to form a ring, which is further bridged by trans ligands to generate one-dimensional chains. Neighbouring chains are stacked via π-π interactions between pyridine rings to give a two-dimensional structure, which is stabilized by π-π interactions between naphthalene rings, forming the final three-dimensional supermolecular network. Solid-state optical diffuse-reflectance spectral studies indicate that compound 4 is a potential wide band gap semiconductor.

Synthesis and Liquid Crystalline Properties of Unsymmetrically Substituted Naphthalenediimides with a Polar Headgroup: Effect of Amide Hydrogen Bonding and Alkyl Chain Length

A series of new unsymmetrically substituted naphthalenediimide (NDI) moieties NDI‐1 to NDI‐6 were synthesized. The structures of these compounds were confirmed by means of FT‐IR, ¹H NMR, ¹³C NMR, ESI‐mass and HRMS spectroscopic measurements. UV/Vis and fluorescence spectroscopy were employed to investigate the photophysical properties of the prepared compounds in solution and in the solid state. Using the onset of UV/Vis absorption, the optical band gaps were calculated. Cyclic voltammetry measurements were performed to study the electrochemical behavior and to calculate the LUMO energy levels. The thermal properties of NDI derivatives were studied by differential scanning calorimetry. The mesomorphic birefringent behavior of the NDI derivatives was investigated with polarizing optical microscopy. Among all of the studied NDI derivatives, only NDI‐1, NDI‐2, and NDI‐3 showed liquid crystalline texture, owing to the presence of an amide linkage for H‐bonding along with aromatic moieties for π–π‐stacking.

A two-dimensional CdII coordination polymer based on naphthalenediimide: synthesis, crystal structure and photochromic properties

Naphthalenediimides, a class of organic dyes with an expanded π-electron-deficient plane, have attracted considerable interest because of their photoinduced electron transfer from neutral organic moieties to stable anionic radicals. This makes them excellent candidates for organic linkers in the construction of photochromic coordination polymers. Such a photochromic two-dimensional coordination polymer has been prepared using N,N'-bis(pyridin-4-ylmethyl)naphthalene-1,8:4,5-bis(dicarboximide) (DPMNI). In crystallization tubes, upon slow diffusion of an MeOH solution of cadmium perchlorate into a CHCl₃ solution of DPMNI, the complex poly[[bis[μ₂-2,7-bis(pyridin-4-ylmethyl)benzo[imn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetrone-κ²N:N']bis(perchlorato-κO)cadmium(II)] chloroform tetrasolvate], {[Cd(C₂₆H₁₆N₄O₄)₂(ClO₄)₂]·4CHCl₃}_n, (I), was obtained. The asymmetric unit contains one Cd²⁺ cation, two DPMNI ligands, two coordinated ClO₄^- anions and four CHCl₃ solvent molecules. Each Cd²⁺ cation is interconnected by four DPMNI linkers to generate a neutral two-dimensional naphthalenediimide coordination network with all the ClO₄^- anions above or below this plane. Strong interlaminar anion-π interactions between the coordinated ClO₄^- anions and the imide rings of an adjacent layer lead to a three-dimensional supramolecular structure. Compound (I) exhibits reversible photochromic behaviour and photocontrolled tunable luminescence properties, which may originate from the photoinduced electron-transfer generation of radicals in the DPMNI ligand.

Excitonically Coupled States in Crystalline Coordination Networks

When chromophores are brought into close proximity, noncovalent interactions (π-π/CH-π) can lead to the formation of excitonically coupled states, which bestow new photophysical properties upon the aggregates. Because the properties of the new states not only depend on the strength of intermolecular interactions, but also on the relative orientation, supramolecular assemblies, where these parameters can be varied in a deliberate fashion, provide novel possibilities for the control of photophysical properties. This work reports that core-substituted naphthalene diimides (cNDIs) can be incorporated into surface-mounted metal- organic structures/frameworks (SURMOFs) to yield optical properties strikingly different from conventional aggregates of such molecules, for example, formed in solution or by crystallization. Organic linkers are used, based on cNDIs, well-known organic chromophores with numerous applications in different optoelectronic devices, to fabricate MOF thin films on transparent substrates. A thorough characterization of the properties of these highly ordered chromophoric assemblies reveals the presence of non-emissive excited states in the crystalline material. Structural modulations provide further insights into the nature of the coupling that gives rise to an excited-state energy level in the periodic structure.

High-Performance, Air-Stable Field-Effect Transistors Based on Heteroatom-Substituted Naphthalenediimide-Benzothiadiazole Copolymers Exhibiting Ultrahigh Electron Mobility up to 8.5 cm V-1 s-1

Rational heteroatom engineering is applied to develop high-performance electron-transporting naphthalenediimide copolymers. Top-gate field-effect transistors fabricated from selenophene-containing polymers achieve an ultrahigh electron mobility of 8.5 cm² V^-1 s^-1 and excellent air-stability. The results demonstrate that the incorporation of selenophene heterocycles into the polymers can improve the film-forming ability, intermolecular interaction, and carrier transport significantly.

Naphthalenediimide Polymers with Finely Tuned In-Chain π-Conjugation: Electronic Structure, Film Microstructure, and Charge Transport Properties

Naphthalenediimide-based random copolymers (PNDI-TVTx) with different π-conjugated dithienylvinylene (TVT) versus π-nonconjugated dithienylethane (TET) unit ratios (x = 100→0%) are investigated. The PNDI-TVTx-transistor electron/hole mobilities are affected differently, a result rationalized by molecular orbital topologies and energies, with hole mobility vanishing but electron mobility decreasing only by ≈2.5 times when going from x = 100% to 40%.

A Naphthalenediimide-Based Fluorescent Sensor for Detecting the pH within the Rough Endoplasmic Reticulum of Living Cells

An amino-core-substituted naphthalenediimide (NDI) derivative has been synthesized in good yield in two steps. The NDI bearing a diamine moiety undergoes a reversible protonation-deprotonation process, which results in intensity changes in the absorption and emission spectra. This derivative exhibits good photostability, good selectivity, high sensitivity, and is employed to exhibit the pH within the rough endoplasmic reticulum of living cells.

Preparation, characterization and in vitro evaluation of sterically stabilized liposome containing a naphthalenediimide derivative as anticancer agent

The aim of this study was to incorporate a new naphthalenediimide derivative (AN169) with a promising anticancer activity into pegylated liposomes to an extent that allows its in vitro and in vivo testing without use of toxic solvent. AN169-loaded liposomes were prepared using the thin-film hydration method and characterized for size, polydispersity index, drug content and drug release. We examined their lyophilization ability in the presence of cryoprotectants (trehalose, sucrose and lysine) and the long-term stability of the lyophilized products stored at 4 °C for 3 and 6 months by particle size changes and drug leakage. AN169 was successfully loaded into liposomes with an entrapment efficiency of 87.3 ± 2.5%. The hydrodynamic diameter of these liposomes after sonication was ∼ 145 nm with a high degree of monodispersity. Trehalose was found to be superior to the other lyoprotectants. In particular, trehalose 1:10 lipid:cryoprotectant molar ratio may provide stable lyophilized liposomes with the conservation of physicochemical properties upon freeze-drying and long-term storage conditions. We also assessed their in vitro antitumor activity in human cancer cell lines (HTLA-230 neuroblastoma, Mel 3.0 melanoma, OVCAR-3 ovarian carcinoma and SV620 prostate cancer cells). However, only after 72 h incubation, loaded liposomes showed almost the same IC50 as free AN169. In conclusion, we developed a stable lyophilized liposomal formulation for intravenous administration of AN169 as anticancer drug, with the advantage of avoiding the use of potentially toxic solubilizing agents for future in vivo experiments.