Synthesis, Stable Radical Anion and Energy Storage Performance of Pentacene Tetraimides

Imide functionalization has been widely proved to be an effective approach to enrich optoelectronic properties of polycyclic aromatic hydrocarbons (PAHs). However, appending multiple imide groups onto linear acenes is still a synthetic challenge. Herein, we demonstrate that by taking advantage of a "breaking and mending" strategy, a linear pentacene tetraimides (PeTI) was synthesized through a three-step sequence started from the naphthalene diimides (NDI). Compared with the parent pentacene, PeTI shows a deeper-lying lowest unoccupied molecular orbital (LUMO) energy level, narrower band gap and better stability. The redox behavior of PeTI was firstly evaluated by generating a stable radical anion specie with the assistance of cobaltocene (CoCp2), and the structure of the electron transfer (ET) complex was confirmed by the X-ray crystallography. Moreover, due to the presence of multiple redox-active sites, we are able to show that the state-of-the-art energy storage performance of the dealkylated PeTI (designated as PeTCTI) in organic potassium ion batteries (OPIBs) as an anode. Our results shed light on the application of multiple imides functionalized linear acenes, and the reported synthetic strategy provides an effective way to get access to longer nanoribbon imides with fascinating electronic properties.

π-Extended S-Heterocyclic Naphthoquinodimethane with Dual Diradical and Dipolar Character

The 2,6-naphthoquinodimethane (2,6-NQDM) containing S-heterocyclic molecule 6-S was synthesized, and its dual open-shell diradical and dipolar characters were revealed via both experimental and theoretical studies. Unlike the shorter p-quinodimethane (p-QDM)-containing analogue 5-S, which possesses a closed-shell ground state (y₀ = 0%) with small dipolar character, 6-S possesses enhanced dipolar character with a singlet diradical ground state (y₀ = 23.3%) and a thermally accessible triplet excited state (ΔE_ST = -4.13 kcal/mol). Despite this, it displays good stability (t_1/2 = 41days) under ambient air and light conditions due to its distinctive dipolar character and kinetic blocking of reactive sites.

Molecular Carbon Imides

The creation and development of new forms of nanocarbons have fundamentally transformed the scientific landscape in the past three decades. As new members of the nanocarbon family with accurate size, shape, and edge structure, molecular carbon imides (MCIs) have shown unexpected and unique properties. Particularly, the imide functionalization strategy has endowed these rylene-based molecular carbons with fascinating characteristics involving flexible syntheses, tailor-made structures, diverse properties, excellent processability, and good stability. This Perspective elaborates molecular design evolution to functional landscapes, and illustrative examples are given, including a promising library of multi-size and multi-dimensional MCIs with rigidly conjugated π-architectures, ranging from 1D nanoribbon imides and 2D nanographene imides to cross-dimensional MCIs. Although researchers have achieved substantial progress in using MCIs as functional components for exploration of charge transport, photoelectric conversion, and chiral luminescence performances, they are far from unleashing their full potential. Developing highly efficient and regioselective coupling/ring-closure reactions involving the formation of multiple C-C bonds and the annulation of electron-deficient aromatic units is crucial. Prediction by theory with the help of machine learning and artificial intelligence research along with reliable nanotechnology characterization will give an impetus to the blossom of related fields. Future investigations will also have to advance toward─or even focus on─the emerging potential functions, especially in the fields of chiral electronics and spin electronics, which are expected to open new avenues.

Flavanthrene derivatives as photostable and efficient singlet exciton fission materials

Singlet exciton fission (SF) is believed to have the potential to break the Shockley−Quiesser third-generation solar cell devices, so that attracted great attention. Conventional linear acene based SF materials generally...

syn/anti-Oligothienoacene Diimides with up to 10 Fused Rings

We report a facile and powerful strategy to prepare libraries of oligothienoacene diimides that include anti- and syn-isomers using palladium-catalyzed C-H activation and an unexpected 1,2-sulfur migration. Through this strategy, a series of oligothienoacene diimides containing 6, 8, and 10 fused rings were synthesized. The molecular geometry and extent of π-conjugation have dramatic effects on the electronic properties, degree of crystallinity, and charge-carrier transport properties. Notably, single-crystal microfibers of syn-3 c show electron mobilities up to 4.2 cm²  V^-1  s^-1 , illustrating the significant potential of these materials for organic electronic devices. Our work demonstrates the versatility of this strategy for the development of oligothienoacene diimide libraries, in particular complex and large syn-oligothienoacene diimides, which are difficult to prepare by present methods.

Red fluorescent zwitterionic naphthalenediimides with di/mono-benzimidazolium and a negatively-charged oxygen substituent

The C-H/C-X cross-coupling of a benzimidazolium salt with 2Br-NDI afforded two unprecedented zwitterionic NDIs with di/mono-benzimidazolium and an extra negatively-charged oxygen substituent. They exhibited intensified red fluorescence in polar solvents and negative solvatochromism due to an intramolecular charge transfer process, and could specifically label lysosomes and the endoplasmic reticulum in living A549 cells, respectively. They represent a rare case of NDI-derived ionic fluorophores.

Cata-Annulated Azaacene Bisimides

Ultra‐electron‐deficient azaacenes were synthesized via Buchwald‐Hartwig coupling of ortho‐diaminoarenes with chlorinated mellophanic diimide followed by oxidation of the intermediate N,N’‐dihydro compounds with MnO₂ or PbO₂. The resulting cata‐annulated bisimide azaacenes have ultrahigh electron affinities with first reduction potentials as low as −0.35 V recorded for a tetraazapentacene. Attempts to prepare a tetrakis(dicarboximide)tetraazaheptacene resulted in the formation of a symmetric butterfly dimer.

Tuning the LUMO Levels of Z-Shaped Perylene Diimide via Stepwise Cyanation

The central dogma in constructing organic electron acceptors is to attach electron-withdrawing groups to polycyclic aromatic hydrocarbons. Yet, the full potentials of many organic acceptors were never realized due to synthetic obstacles. By combining the Wittig-Knoevenagel benzannulation, the Pd(0)-catalyzed cyanation, and nucleophilic addition/oxidation cyanation, six polynitrile Z-shaped perylene diimide were synthesized. These stable and soluble electron acceptors possess LUMO energy levels comparable with those of benchmark compounds. Electrochemical investigation reveals that each additional nitrile group reduces the LUMO energy by 0.2 eV.

A Tetraindeno-Fused Bis(anthraoxa)quinodimethane with Nine Consecutively Fused Six-Membered Rings

A tetraindeno-fused bis(anthraoxa)quinodimethane RBR with nine consecutively fused six-membered rings in a row was synthesized. Its structure was confirmed by X-ray crystallographic analysis and NMR measurement. Compared with an unfused analogue ABA, the indeno fusion onto the zigzag edges not only enhanced the photostability but also dramatically tuned the electronic properties. Due to the existence of two rubicene units, RBR can also be readily reduced to form a radical anion and dianion.

Isomeric anthracene diimide polymers

N-type semiconducting polymers are attractive for organic electronics, but desirable electron-deficient units for synthesizing such polymers are still lacking. As a cousin of rylene diimides such as naphthalene diimide (NDI) and perylene diimide (PDI), anthracene diimide (ADI) is a promising candidate; its polymers, however, have not been achieved yet because of synthetic challenges for its polymerizable monomers. Herein, we present ingenious synthesis of two dibromide ADI monomers with dibromination at differently symmetrical positions of the ADI core, which are further employed to construct ADI polymers. More interestingly, the two obtained ADI polymers possess the same main-chain and alkyl-chain structures but different backbone conformations owing to varied linking positions between repeating units. This feature enables their different optoelectronic properties and film-state packing behavior. The ADI polymers offer first examples of conjugated polymer conformational isomers and are highly promising as a new class of n-type semiconductors for various organic electronics applications.

Influence of the solvent environment on luminescent centers within carbon dots

Carbon dots (CDs) are luminescent nanomaterials, with potential use in bioimaging and sensorics. Here, the influence of the surrounding solvent media on the optical properties of CDs synthesized from the most commonly employed precursors, namely citric acid and ethylenediamine, is investigated. The position of optical transitions of CDs can be tuned by the change of pH and solvent polarity. The most striking observation is related to the interaction of CDs with chlorine containing solvents, which results in resolving a set of narrow peaks within both the absorption and PL bands, similar to those observed for polycyclic aromatic hydrocarbons or organic dyes. We assume that the chlorine containing molecules penetrate the surface layers of CDs, which results in an increase of the distance between the luminescent centers; this correlates well with an enhanced D-band in their Raman spectra. A model of CDs composed of a matrix of hydrogenated amorphous carbon with the inclusions of sp2-domains formed by polycyclic aromatic hydrocarbons and their derivatives is suggested; the latter are stacked ensembles of the luminophores and are considered as the origin of the emission of CDs.

Reduced Knoevenagel Reaction of Acetetracenylene-1,2-dione with Acceptor Units for Luminescent Tetracene Derivatives

Acetetracenylene-1,2-dione reacted with 3-ethylrhodanine in the presence of piperidine and Hantzsch ester via a Knoevenagel condensation-reduction sequence to give a tetracene-rhodanine adduct. This reduced Knoevenagel product exhibited magenta luminescence with a fluorescence quantum yield of φ = 0.34 and fluorescence lifetime of τ = 13.2 ns in toluene. Electrochemical studies and charge carrier transport measurements revealed ambipolar properties with hole and electron mobilities of 5.1 × 10^-7 and 1.6 × 10^-4 cm²/(V s), respectively.

Theoretical investigations into the charge transfer properties of thiophene α-substituted naphthodithiophene diimides: excellent n-channel and ambipolar organic semiconductors

A theoretical study was carried out to investigate the electronic structures and the charge transport properties of a series of naphthodithiophene diimide (NDTI) thiophene α-substituted derivatives NDTI-X using density functional theory and classical Marcus charge transfer theory. This study deeply revealed the structure-property relationships by analyzing the intermolecular interactions in crystal structures of C8-NDTI and C8-NDTI-Cl thoroughly by using the Hirshfeld surface, QTAIM theories and symmetry-adapted perturbation theory (SAPT). Our results suggested that a 2-D brick-like π-stacking structure makes C8-NDTI-Cl a more excellent n-type semiconducting material with μ_max-e of 2.554 cm² V^-1 s^-1 than C8-NDTI with a herringbone-like slipped π-stacking motif. In addition, the calculated results showed that by modifying the thiophene α-positions of NDTI with electron-withdrawing substituents, -F, -Cl and -CN, low-lying LUMO energy levels and a high adiabatic electron affinity EA(a) can be obtained; while introducing electron-donating groups, benzene (-B), thiophene (-T), benzo[b]thiophene (-BT) and naphtha[2,3-b]thiophene (-NT), expanded the molecular π-conjugated backbone, and narrow band gaps, high EA(a) and small reorganization energies can be obtained. Theoretical simulations predict that NDTI-CN is an excellent air-stable n-type organic semiconducting material with an average electron mobility μ_e of up to 1.743 cm² V^-1 s^-1. Owing to their high EA(a), moderate adiabatic ionization potential IP(a) as well as small hole and electron reorganization energies, NDTI-BT and NDTI-NT are two well-balanced air-stable ambipolar semiconducting materials. The theoretical average hole/electron mobilities are as high as 2.708/3.739 cm² V^-1 s^-1 for C8-NDTI-NT and 1.597/2.350 cm² V^-1 s^-1 for C8-NDTI-BT, respectively.

Carbocyclization approaches to electron-deficient nanographenes and their analogues

Versatile π-aromatic building blocks and selective coupling transformations enable rapid assembly of complex electron-deficient molecules, useful as n-type organic semiconductors.

Fluoroalkyl-modified naphthodithiophene diimides

Two kinds of fluoroalkyl-modified naphthodithiophene diimides (NDTI) were designed and synthesized. α-Modified NDTI could form favorable slipped one-dimensional (1D) stacking and N-modified NDTI shows a torsion cofacial stacking. Single-crystal transistors confirm that both fluoroalkyl-modified NDTI possess good electron transport ability with electron mobilities of 0.065 cm² V^-1 s^-1 and 1.59 cm² V^-1 s^-1, respectively.

Synthesis, physical properties, and chemistry of donor–acceptor-substituted pentacenes

Pentacenes bearing electron-donating and (or) -withdrawing groups, namely methoxy-, dialkylamino-, and nitroaryl moieties, are synthesized to afford polarized pentacenes. The optical, electrochemical, and chemical properties of these derivatives are explored. The cycloaddition reaction of selected derivatives with tetracyanoethylene (TCNE) is explored, and the experimental results are rationalized on the basis calculations using density functional theory (DFT). X-ray crystallographic data provides insight into the molecular structure and intermolecular interactions present in the solid state.

N,N'-Bis(2-cyclohexylethyl)naphtho[2,3-b:6,7-b']dithiophene Diimides: Effects of Substituents

Naphtho[2,3-b:6,7-b']dithiophene-4,5,9,10-tetracarboxylic diimide (NDTI) is a promising electron-deficient building block for n-type organic conductors, and the performance of NDTI-based field-effect transistors (FETs) is largely dependent on the substituents that alter the supramolecular organization in the solid state and, in turn, the intermolecular orbital overlap. For this reason, the rational selection of substituent on imide nitrogen atoms and/or thiophene α-positions is the key to developing superior n-type organic semiconductors. We here report new NDTI derivatives having N-(2-cyclohexylethyl) groups. Despite their one-dimensional packing structures in the solid state regardless of the presence or absence of chlorine groups at the thiophene α-positions, their FETs show promising performance with electron mobilities higher than 0.1 cm²·V(-1)·s(-1) under ambient conditions. We also discuss how the cyclohexylethyl groups affect the packing structure in comparison with analogous n-octyl derivatives having the same number of carbon atoms.

Toward electron-deficient pyrene derivatives: construction of pyrene tetracarboxylic diimide containing five-membered imide rings

Electron-deficient pyrene-1,2,6,7-tetracarboxylic diimide (PyrDI) and pyrene-4,9-dicyano-1,2,6,7-tetracarboxylic diimide (PyrDI-CN) containing five-membered imide rings have been designed and synthesized as a new family of aromatic diimides.

Strategies for the synthesis of functional naphthalene diimides

Naphthalene diimides, which have for a long time been in the shadow of their higher homologues the perylene diimides, currently belong to the most investigated classes of organic compounds. This is primarily due to the initial synthetic studies on core functionalization that were carried out at the beginning of the last decade, which facilitated diverse structural modifications of the naphthalene scaffold. Compounds with greatly modified optical and electronic properties that can be easily and effectively modulated by appropriate functionalization were made accessible through relatively little synthetic effort. This resulted in diverse interesting applications. The electron-deficient character of these compounds makes them highly valuable, particularly in the field of organic electronics as air-stable n-type semiconductors, while absorption bands over the whole visible spectral range through the introduction of core substituents enabled interesting photosystems and photovoltaic applications. This Review provides an overview on different approaches towards core functionalization as well as on synthetic strategies for the core expansion of naphthalene diimides that have been developed mainly in the last five years.

Imides modified benzopicenes: synthesis, solid structure and optoelectronic properties

Imide-modified polycyclic aromatic hydrocarbons can be widely applied in the field of optoelectronic materials.