Conjugated Naphthalenediimide-Pyridinium Salts in Donor-Acceptor Hybrid Materials for Enhanced Photochromic Properties

As an emerging class of hybrid materials, donor-acceptor (D-A) hybrid crystals with photoactive organic and inorganic components have gradually become an ideal platform for photochromic materials. Wherein the most available organic components are electron-poor naphthalenediimide, pyridinium, and triazine derivatives, inorganic units are electron-rich polyoxometalates and metal halides. Herein, we introduced pyridinium moieties into the naphthalenediimide core by conjugated bonds so as to increase the electron deficiency of organic species for enhanced photochromic properties. Four anion-π interaction directed hybrid crystals, (Me2DPNDI)3·(PW12O40)2 (1), (Et2DPNDI)3·(DMSO)2·(PMo12O40)2 (2), (Et2DPNDI)3·(PW12O40)2 (3), and (Et2DPNDI)2·(SiMo12O40) (4), have been obtained, which possess reversible, naked-eye perceptible color changes with varying light response rates. These rates are as follows: 3 > 1 > 4 > 2. As expected, such D-A hybrid crystals with conjugated naphthalenediimide-pyridinium salts feature both photo- and thermally induced electron transfer pathways, along with enhanced anion-π interactions. Consequently, they demonstrate a higher rate of photochromism compared to those of hybrids containing naphthalenediimide or pyridinium derivatives as organic acceptors.

Synthesis and Properties of Electron-Deficient and Electron-Rich Redox-Active Ionic π-Systems

There is growing interest towards the design and synthesis of organic redox-active systems, which exist in ionic form. Multi- redox systems entail life-sustaining processes like photosynthesis and cellular respiration. The significant challenge for material scientists is to rationally design complex molecular materials that can store and transfer multiple electrons at low operational potentials and are stable under ambient conditions. Also, important are the designed ionic π-systems that combine efficient electron and ion transport. Here, we discuss the synthesis of ionic π-systems which exist in the closed-shell form. Firstly, different classes of ionic arylenediimides and viologens with different π-linkers are discussed from the synthetic, structural and redox perspective. These ionic π-systems are based on the electron deficient π-scaffolds, and are shown to accumulate upto six electrons. We then discuss electron-rich ionic arylenediimides which can exist in anionic form or zwitterionic form. The anionic electron donors have absorption extending to the near Infrared (NIR) region and can be stabilized in aqueous solution. We also discuss the effect of the electron accumulation on the aromaticity and non-aromaticity of the naphthalene and the imide rings of the naphthalenediimides. We finally discuss in brief, the applications related to the organic mixed ionic-electronic conductors.

Anion-π Catalysis Enabled by the Mechanical Bond

We report a series of rotaxane-based anion-π catalysts in which the mechanical bond between a bipyridine macrocycle and an axle containing an NDI unit is intrinsic to the activity observed, including a [3]rotaxane that catalyses an otherwise disfavoured Michael addition in >60 fold selectivity over a competing decarboxylation pathway that dominates under Brønsted base conditions. The results are rationalized by detailed experimental investigations, electrochemical and computational analysis.

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.

Naphthalene diimides: perspectives and promise

In this review, we describe the developments in the field of naphthalene diimides (NDIs) from 2016 to the presentday. NDIs are shown to be an increasingly interesting class of molecules due to their electronic properties, large electron deficient aromatic cores and tendency to self-assemble into functional structures. Almost all NDIs possess high electron affinity, good charge carrier mobility, and excellent thermal and oxidative stability, making them promising candidates for applications in organic electronics, photovoltaic devices, and flexible displays. NDIs have also been extensively studied due to their potential real-world uses across a wide variety of applications including supramolecular chemistry, sensing, host-guest complexes for molecular switching devices, such as catenanes and rotaxanes, ion-channels, catalysis, and medicine and as non-fullerene accepters in solar cells. In recent years, NDI research with respect to supramolecular assemblies and mechanoluminescent properties has also gained considerable traction. Thus, this review will assist a wide range of readers and researchers including chemists, physicists, biologists, medicinal chemists and materials scientists in understanding the scope for development and applicability of NDI dyes in their respective fields through a discussion of the main properties of NDI derivatives and of the status of emerging applications.

Exploring the structure-property schemes in anion-π systems of d-block metalates

Anion-π based compounds, materials, and processes have gained significant interest due to the diversity of their aesthetic non-covalent synthons, and thanks to their significance in biological systems, catalytic processes, anion binding and sensing, or the supramolecular organization of hierarchical architectures. While systems based on typical inorganic anions or organic residues have been widely reviewed in recent years, those involving anionic d metal comlexes as the main components have been treated with a rather secondary interest. However, actively exploring the new systems of the latter type we have recognized systematic advances in the field. As a result, in the current review we describe the landscape that has recently emerged. Focusing on the established groups of π-acidic species, i.e. polycarbonitirles, polyazines, polyazine N-oxides, diimide derivatives, fluoroarenes, and nitroarenes, we explore and discuss anion-π crystal engineering together with the structure-property schemes important from the standpoint of charge transfer (CT) and electron transfer (ET), magnetism, luminescence, reactivity and catalysis, and the construction of core-shell crystalline composites.

Azine Steric Hindrances Switch Halogen Bonding to N-Arylation upon Interplay with σ-Hole Donating Haloarenenitriles

An interplay between 4-bromo- and 4-iodo-5-nitrophthalonitriles (XNPN, X=Br or I) and any one of the azines (pyridine 1, 4-dimethylaminopyridine 2, isoquinoline 3, 4-cyanopyridine 4, 2-methylpyridine 5, 2-aminopyridine 6, quinoline 7, 1-methylisoquinoline 8, and 2,2'-bipyridine 9) proceeds differently depending on steric and electronic effects of the heterocycles. Sterically unhindered azines 1-3 underwent N-arylation to give the corresponding azinium salts (characterized by ¹ H and ¹³ C{H} NMR and high-resolution ESI-MS). In contrast, azines 4-9 with sterically hindered N atoms or bearing an electron-withdrawing substituent, form stable co-crystals with XNPN, where two interacting molecules are bound by halogen bonding. In all obtained co-crystals, X⋅⋅⋅N structure-directed halogen bonds were recognized and theoretically evaluated including DFT calculations (PBE0-D3/def2-TZVP level of theory), QTAIM analysis, molecular electrostatic potential surfaces, and noncovalent interaction plot index. Estimated energies of halogen bonding vary from -7.6 kcal/mol (for 6 ⋅ INPN) to -11.4 kcal/mol (5 ⋅ INPN).

Targeted Synthesis of NIR Luminescent Rhenium Diimine cis,trans-[Re( N N )(CO)2 (L)2 ]n+ Complexes Containing N-Donor Axial Ligands: Photophysical, Electrochemical, and Theoretical Studies

The combined action of ultraviolet irradiation and microwave heating onto acetonitrile solution of [Re( N N )(CO)₃ (NCMe)]OTf ( N N =phenantroline and neocuproine) afforded cis,trans-Re( N N )(CO)₂ (NCMe)₂ ]⁺ acetonitrile derivatives. Substitution of relatively labile NCMe with a series of aromatic N-donor ligands (pyridine, pyrazine, 4,4'-bipyridine, N-methyl-4,4'-bipyridine) gave a novel family of the diimine cis,trans-[Re( N N )(CO)₂ (L)₂ ]⁺ complexes. Photophysical studies of the obtained compounds in solution revealed unusually high absorption across the visible region and NIR phosphorescence with emission band maxima ranging from 711 to 805 nm. The nature of emissive excited states was studied using DFT calculations to show dominant contribution of ³ MLCT (dπ(Re)→π*( N N )) character. Electrochemical (CV and DPV) studies of the monocationic diimine complexes revealed one reduction and one oxidation wave assigned to reduction of the diimine moiety and oxidation of the rhenium center, respectively.

Naphthalenediimides with Cyclic Oligochalcogenides in Their Core

Naphthalenediimides (NDIs) are privileged scaffolds par excellence, of use in functional systems from catalysts to ion channels, photosystems, sensors, ordered matter in all forms, tubes, knots, stacks, sheets, vesicles, and colored over the full visible range. Despite this extensively explored chemical space, there is still room to discover core-substituted NDIs with fundamentally new properties: NDIs with cyclic trisulfides (i.e., trisulfanes) in their core absorb at 668 nm, emit at 801 nm, and contract into disulfides (i.e., dithietes) upon irradiation at <475 nm. Intramolecular 1,5-chalcogen bonds account for record redshifts with trisulfides, ring-tension mediated chalcogen-bond-mediated cleavage for blueshifts to 492 nm upon ring contraction. Cyclic oligochalcogenides (COCs) in the NDI core open faster than strained dithiolanes as in asparagusic acid and are much better retained on thiol exchange affinity columns. This makes COC-NDIs attractive not only within the existing multifunctionality, particularly artificial photosystems, but also for thiol-mediated cellular uptake.

The role of fluoride in anion–π interaction with naphthalene diimide

The role of fluoride in anion–π interaction with naphthalene diimide (NDI) is dependent on the solvent used.

Anion–π and anion–π-radical interactions in bis(triphenylphosphonium)-naphthalene diimide salts

Anion–π-radical interaction plays a key role in photophysical and magnetic properties.