Understanding Charge-Transfer Characteristics in Crystalline Nanosheets of Fullerene/(Metallo)porphyrin Cocrystals

Recent advances in supramolecular fullerene chemistry

Fullerene chemistry has come a long way since 1990, when the first bulk production of C60 was reported. In the past decade, progress in supramolecular chemistry has opened some remarkable and previously unexpected opportunities regarding the selective (multiple) functionalization of fullerenes and their (self)assembly into larger structures and frameworks. The purpose of this review article is to provide a comprehensive overview of these recent developments. We describe how macrocycles and cages that bind strongly to C60 can be used to block undesired addition patterns and thus allow the selective preparation of single-isomer addition products. We also discuss how the emergence of highly shape-persistent macrocycles has opened opportunities for the study of photoactive fullerene dyads and triads as well as the preparation of mechanically interlocked compounds. The preparation of two- or three-dimensional fullerene materials is another research area that has seen remarkable progress over the past few years. Due to the rapidly decreasing price of C60 and C70, we believe that these achievements will translate into all fields where fullerenes have traditionally (third-generation solar cells) and more recently been applied (catalysis, spintronics).

Sorting and Screening of Quaternary Ammonium Lipoids for Membrane-Binding Assays Based on Electrochemiluminescent Cocrystalline Nanosheets

Being synthetic supplements to natural lipids, lipoids now play an increasingly significant role in nanopore sequencing, olfactory sensing, and nanoimpact electrochemistry. Yet, systematic comparisons to sort and screen qualified lipoids are lacking for specific scenario applications. Here, taking the merits of electrochemiluminescence (ECL) in probing biointerfacial events, a new metric was proposed for the evaluation of substrate candidacy in the pool of hyamine bromides (ABs), that are used to cohere with electron-rich porphyrins for deep eutectics-like ECL matrices. Using a state-of-the-art framework emitter, the cocrystalline nanosheet of C₇₀ and zinc meso-tetraphenylporphine (ZnTPP) via simple liquid-liquid interfacial deposition, 6 out of 20 ABs were inspected and identified as not only amenable filmogens but excitonic sensitizers in key terms of ECL strength as well as voltammetric characteristics. Among them, the methyltrioctyl (MTOAB) headgroup stood out; while the ECL activity at ZnTPP-C₇₀@MTOAB was proven to be dictated by ionophoresis across multilamellar lipoidal layers. Thus, target-induced membrane deformation would let coreactant scavengers in to quench ECL, which enabled assays on two less visited bioprocesses regarding (1) the lipid solubility of ipratropium bromide, an aerosol medication for rhinitis treatment; and (2) the resorption of selenosugar as the central metabolite of Se-proteins on kidney glomerular basement barrier. Both resulted in nice membrane-binding measurements with comparable dissociation constants to reported microfluidic ELISA methods. By and large, though still being rudimentary, such parametrization of ECL-able biofilm would set up a basic ECL toolbox for archiving and resourcing multilipoidal even lipid-lipoid combos to handle the realistic (sub)cytomembrane processes in the future.

Supramolecular Engineering of Crystalline Fullerene Micro-/Nano-Architectures

Fullerenes are a molecular form of carbon allotrope and bear certain solubility, which allow the supramolecular assembly of fullerene molecules-also together with other complementary compound classes-via solution-based wet processes. By well-programmed organizing these building blocks and precisely modulating over the assembly process, supramolecularly assembled fullerene micro-/nano-architectures (FMNAs) are obtained. These FMNAs exhibit remarkably enhanced functions as well as tunable morphologies and dimensions at different size scales, leading to their applications in diverse fields. In this review, both traditional and newly developed assembly strategies are reviewed, with an emphasis on the morphological evolution mechanism of FMNAs. The discussion is then focused on how to precisely regulate the dimensions and morphologies to generate functional FMNAs through solvent engineering, co-crystallization, surfactant incorporation, or post-fabrication treatment. In addition to C₆₀ -based FMNAs, this review particularly focuses on recently fabricated FMNAs comprising higher fullerenes (e.g., C₇₀ ) and metallofullerenes. Meanwhile, an overview of the property modulation is presented and multidisciplinary applications of FMNAs in various fields are summarized, including sensors, optoelectronics, biomedicines, and energy. At the end, the prospects for future research, application opportunities, and challenges associated with FMNAs are proposed.

Electron Donor-Acceptor Interface of TPPS/PDI Boosting Charge Transfer for Efficient Photocatalytic Hydrogen Evolution

Charge separation efficiency of photocatalysts is still the key scientific issue for solar-to-chemical energy conversion. In this work, an electron donor-acceptor (D-A) interface with high charge separation between TPPS (tetra(4-sulfonatophenyl)porphyrin) and PDI (perylene diimide) is successfully constructed for boosting photocatalytic H₂ evolution. The TPPS/PDI with D-A interface shows excellent photocatalytic H₂ evolution rate of 546.54 µmol h^-1 (30.36 mmol h^-1 g^-1 ), which is 9.95 and 9.41 times higher than that of pure TPPS and PDI, respectively. The TPPS/PDI has a markedly stronger internal electric field, which is respectively 3.76 and 3.01 times higher than that of pure PDI and TPPS. The D-A interface with giant internal electric field efficiently facilitates charge separation and urges TPPS/PDI to have a longer excited state lifetime than single component. The work provides entirely new ideas for designing materials with D-A interface to realize high photocatalytic activity.

Cocrystallization tailoring radiative decay pathways for thermally activated delayed fluorescence and room-temperature phosphorescence emission

Modulation of excited-state processes in binary organic cocrystals has been rarely explored so far. Here, we develop two charge-transfer (CT) cocrystal microrods with a 1 : 1 stoichiometric ratio where halogenated dibenzothiophene (DBT) compounds act as π-electron donors and 1,2,4,5-tetracyanobenzene (TCNB) acts as an acceptor. Unexpectedly, the cocrystal containing one bromine (Br) atom at the 3-position of DBT (3-BrTC) presents thermally activated delayed fluorescence (TADF), while the other one comprising one Br atom at the 4-position of DBT (4-BrTC) exhibits both TADF and room-temperature phosphorescence (RTP). Experimental and theoretical calculation results reveal that CT interactions in 3- and 4-BrTC decrease the S₁-T₂ energy gap, whereas abundant lone-pair electrons from the Br atom in 4-BrTC facilitate the n → π* transition. As a consequence, single TADF and dual-emissive TADF/RTP were realized, respectively. The present work offers wonderful insight into the effect of molecular structures on the excited-state pathways of organic CT cocrystals.

Rubrene-Directed Structural Transformation of Fullerene (C60) Microsheets to Nanorod Arrays with Enhanced Photoelectrochemical Properties

One-dimensional (1D) nanostructures possess huge potential in electronics and optoelectronics, but the axial alignment of such 1D structures is still a challenging task. Herein, we report a simple method that enables two-dimensional (2D) C₆₀ microsheets to evolve into highly ordered nanorod arrays using rubrene as a structure-directing agent. The structural transformation is accomplished by adding droplets of rubrene-m-xylene solution onto C₆₀ microsheets and allowing the m-xylene solvent to evaporate naturally. In sharp contrast, when rubrene is absent from m-xylene, randomly oriented C₆₀ nanorods are produced. Spectroscopic and microscopic characterizations collectively indicate a rather plausible transformation mechanism that the close lattice match allows the epitaxial growth of rubrene on C₆₀ microsheets, followed by the reassembly of dissolved C₆₀ along the aligned rubrene due to the intermolecular charge-transfer (CT) interactions, leading to the formation of ordered nanorod arrays. Due to the aligned structures and the CT interactions between rubrene and C₆₀, the photocurrent density of the nanorod arrays is improved by 31.2% in the UV region relative to the randomly oriented counterpart. This work presents a facile and effective strategy for the construction of ordered fullerene nanorod arrays, providing new ideas for the alignment of fullerene and other relevant organic microstructures.

Self-Assembled Corn-Husk-Shaped Fullerene Crystals as Excellent Acid Vapor Sensors

Low-molecular-weight acid vapors cause aging and destruction in material processing. In this paper, facile fabrication of novel corn-husk-shaped fullerene C60 crystals (CHFCs) through the dynamic liquid–liquid interfacial precipitation method is reported. The CHFCs were grown at the liquid–liquid interface between isopropyl alcohol (IPA) and a saturated solution of C60 in mesitylene under ambient temperature and pressure conditions. The average length, outer diameter, and inner diameter of CHFCs were ca. 2.88 μm, 672 nm, and 473 nm, respectively. X-ray diffraction (XRD) analysis showed the CHFCs exhibit a mixed face-centered cubic (fcc) and hexagonal-close pack (hcp) crystal phases with lattice parameters a = 1.425 nm, V = 2.899 nm3 for fcc phase and a = 2.182 nm, c = 0.936 nm, a/c ratio = 2.33, and V = 3.859 nm3 for hcp phase. The CHFCs possess mesoporous structure as confirmed by transmission electron microscopy (TEM) and nitrogen sorption analysis. The specific surface area and the pore volume were ca. 57.3 m2 g−1 and 0.149 cm3 g−1, respectively, are higher than the nonporous pristine fullerene C60. Quartz crystal microbalance (QCM) sensing results show the excellent sensing performance CHFCs sensitive to acetic acid vapors due to the enhanced diffusion via mesoporous architecture and hollow structure of the CHFCs, demonstrating the potential of the material for the development of a new sensor system for aliphatic acid vapors sensing.

Organic Cocrystals: Recent Advances and Perspectives for Electronic and Magnetic Applications

Cocrystal engineering is an advanced supramolecular strategy that has attracted a lot of research interest. Many studies on cocrystals in various application fields have been reported, with a particular focus on the optoelectronics field. However, few articles have combined and summarized the electronic and magnetic properties of cocrystals. In this review, we first introduce the growth methods that serve as the basis for realizing the different properties of cocrystals. Thereafter, we present an overview of cocrystal applications in electronic and magnetic fields. Some functional devices based on cocrystals are also introduced. We hope that this review will provide researchers with a more comprehensive understanding of the latest progress and prospects of cocrystals in electronic and magnetic fields.

Creating Organic Functional Materials beyond Chemical Bond Synthesis by Organic Cocrystal Engineering

Organic cocrystal engineering refers to two or more organic molecules stoichiometrically combined and held together by noncovalent intermolecular interactions, which differs from standard chemical synthesis involving covalent bond breakage and formation. Organic cocrystals have unique properties and offer a new strategy for creating enhanced organics. First, however, some key questions need to be addressed: How do diverse monomers affect the intermolecular interaction kinetics during cocrystallization? How do the intermolecular forces in cocrystals affect cocrystal functions? In this Perspective, the definition and advantages of organic cocrystal engineering, specifically in the construction of a reliable intermolecular interaction-stacking structure-performance relationship, are outlined. Additionally, recent developments in the field and the questions above are discussed. Finally, a brief conclusion and some hints on likely future developments are provided.

Functional Carbazole-Fullerene Complexes: A New Perspective of Carbazoles Acting as Nano-Octopus to Capture Globular Fullerenes

Fullerene host-guest constructs have attracted increasing attention owing to their molecular-level hybrid arrangements. However, the usage of simple carbazolic derivatives to bind with fullerenes is rare. In this research, three novel carbazolic derivatives, containing a tunable bridging linker and carbazole units for the capturing of fullerenes, are rationally designed. Unlike the general concave-convex interactions, fullerenes could interact with the planar carbazole subunits to form 2-dimensional hexagonal/quadrilateral cocrystals with alternating stacking patterns of 1 : 1 or 1 : 2 stoichiometry, as well as the controllable fullerene packing modes. At the meanwhile, good electron-transporting performances and significant photovoltaic effects were realized when a continuous C_60⋅⋅⋅ C₆₀ interaction channel existed. The results indicate that the introduction of such carbazolic system into fullerene receptor would provide new insights into novel fullerene host-guest architectures for versatile applications.

From 3D hierarchical microspheres to 1D microneedles: the unique role of water in the morphology control of ferrocenylpyrrolidine C60 microcrystals

Fullerene microcrystals have been well prepared by the conventional liquid-liquid interface precipitation (LLIP) method, and the crystal structures can be manipulated by solvent combination. Aromatic and alcoholic solvents are widely used as good and poor solvents, respectively, in LLIP. However, water with higher polarity has been rarely utilized as a poor solvent for the morphology engineering of fullerenes, particularly in the morphology control of fullerene derivatives. Herein, the water-regulated morphology of a fullerene derivative, namely ferrocenylpyrrolidine C₆₀ (denoted as FC), is investigated via the LLIP method. By simply modulating the combination of a good solvent (aromatic isopropylbenzene, IPB) and the poor solvents (alcohols), three-dimensional (3D) hierarchical microspheres of FC are obtained. Surprisingly, when water is introduced as one of poor solvents in the LLIP process, one-dimensional (1D) microneedles are obtained. The presence of water controls the liquid-liquid interface, the external environment and kinetics of the crystal growth, thereby promoting the morphological evolution from 3D hierarchical microspheres to 1D microneedles. Moreover, the solvated 1D microneedles exhibit enhanced photoluminescence (PL) and photocurrent responses in virtue of the highly ordered molecule arrangement and solvent (IPB) embedding in the crystal lattice. The water-regulated morphology engineering of FC provides a new strategy for the growth and morphology control of fullerene microcrystals.

The shape selectivity of corannulene dimers based on concave-convex and convex-convex shape complementarity as hosts for C60 and C70

In the formation of noncovalent complexes, the stacking arrangements of corannulene and fullerene are diverse, most of which are combinations of multiple corannulenes and fullerene. Here, a composition ratio of 2 : 1 was selected for the complex between corannulene and fullerene (C60 and C70) to investigate the effects of different superposition modes, including concave-convex and convex-convex interactions, on the stability and third-order nonlinear optical (NLO) properties of the composite materials. It was found that the concave-convex interaction was stronger and it was reported to stabilize the charge-transfer (CT) complex more effectively than the convex-convex interaction. The dispersion range of the concave-convex interaction was larger than that of the convex-convex interaction, which is consistent with the interaction energy results. The packing design with the double convex-convex interactions exhibited the largest linear optical response and third-order NLO response, which showed that the convex-convex interaction was more likely to be excited and cause intermolecular CT as compared to the concave-convex interaction. This work confirmed that the packing arrangement significantly affected the NLO response and will advance the development of NLO crystals.

Glassy Porphyrin/C60 Composites: Morphological Engineering of C60 Fullerene with Liquefied Porphyrins

Morphological control of C₆₀ fullerene using liquefied porphyrins (1 and 2) as the host matrices was explored. Slow evaporation of the solvent of the equimolar mixture of porphyrin and C₆₀ in toluene afforded the porphyrin/C₆₀ composite with a 3:1 molar ratio. The stoichiometric binding behaviors suggest that specific porphyrin-C₆₀ interactions operate the formation of the porphyrin/C₆₀ composites, as corroborated by spectroscopic and thermal properties, and glazing-incidence wide-angle X-ray diffraction. Under the bulk conditions, the conventional thermodynamic advantage of multiple binding cooperativity for molecular recognition is unlikely to explain the stoichiometric binding behaviors. Instead, we propose a size-matching effect on the porphyrin-C₆₀ interaction in the bulk porphyrin matrices, i.e., "supramolecular solvation". The glassy nature of the porphyrin matrices was transmitted to C₆₀ through the specific interaction, and the porphyrin/C₆₀ composites adopted glassy states at room temperature.

Multifunctional Features of Organic Charge-Transfer Complexes: Advances and Perspectives

The recent progress of charge-transfer complexes (CTCs) for application in many fields, such as charge transport, light emission, nonlinear optics, photoelectric conversion, and external stimuli response, makes them promising candidates for practical utility in pharmaceuticals, electronics, photonics, luminescence, sensors, molecular electronics and so on. Multicomponent CTCs have been gradually designed and prepared as novel organic active semiconductors with ideal performance and stability compared to single components. In this review, we mainly focus on the recently reported development of various charge-transfer complexes and their performance in field-effect transistors, light-emitting devices, lasers, sensors, and stimuli-responsive behaviors.

One-Dimensional Fullerene/Porphyrin Cocrystals: Near-Infrared Light Sensing through Component Interactions

Recently, organic donor-acceptor (D-A) cocrystals have attracted special interest as functional materials because of their unique chemical and physical properties that are not exhibited by simple mixtures of their components. Herein, we report the preparation of one-dimensional novel D-A cocrystals from C₆₀ and 5,10,15,20-tetrakis(3,5-dimethoxyphenyl)porphyrin (3,5-TPP); these cocrystals have near-infrared (NIR) light-sensing abilities, despite each of their component molecule individually having no NIR light-sensing properties. Micrometer-sized rectangular columnar C₆₀-3,5-TPP cocrystals were produced by a simple liquid-liquid interfacial precipitation method. The cocrystals exhibit a new strong transition in the NIR region indicative of the existence of charge-transfer interactions between C₆₀ and 3,5-TPP in the cocrystals. The C₆₀-3,5-TPP cocrystals showed n-type transport characteristics with NIR light-sensing properties when the cocrystals were incorporated in bottom-gate/bottom-contact organic phototransistors, revealing that organic cocrystals with suitable charge-transfer interaction are useful as functional materials for the creation of novel NIR-light-sensing devices.

Tailoring structural features and functions of fullerene rod crystals by a ferrocene-modified fullerene derivative

Effective functional intercalation and facile structural manipulation of fullerene crystals could be achieved by ferrocene-modified fullerene based on the liquid–liquid interfacial precipitation process.

Organic Electron Delocalization Modulated by Ligand Charge States in [L2M]n- Complexes of Group 13 Ions

Water-stable organic mixed valence (MV) compounds have been prepared by the reaction of reduced bis(imino)pyridine ligands (I₂P) with the trichloride salts of Al, Ga, and In. The coordination of two tridentate ligands to each ion affords octahedral complexes that are accessible with five ligand charge states: [(I₂P⁰)(I₂P^-)M]²⁺, [(I₂P^-)₂M]⁺, (I₂P^-)(I₂P^2-)M, [(I₂P^2-)₂M]^-, and [(I₂P^2-)(I₂P^3-)M]^2-, and for M = Al only, [(I₂P^3-)₂M]^3-. In solid-state structures, the anionic members of the redox series are stabilized by the intercalation of Na⁺ cations within the ligands. The MV members of the redox series, (I₂P^-)(I₂P^2-)M and [(I₂P^2-)(I₂P^3-)M]^2-, show characteristic intervalence transitions, in the near-infrared regions between 6800-7400 and 7800-9000 cm^-1, respectively. Cyclic voltammetry (CV), NIR spectroscopic, and X-ray structural studies support the assignment of class II for compounds [(I₂P^2-)(I₂P^3-)M]^2- and class III for M = Al and Ga in (I₂P^-)(I₂P^2-)M. All compounds containing a singly reduced I₂P^- ligand exhibit a sharp, low-energy transition in the 5100-5600 cm^-1 region that corresponds to a π*-π* transition. CV studies demonstrate that the electron-transfer events in each of the redox series, Al, Ga, and In, span 2.2, 1.4, and 1.2 V, respectively.

Cocrystal Engineering: A Collaborative Strategy toward Functional Materials

Cocrystal engineering with a noncovalent assembly feature by simple constituent units has inspired great interest and has emerged as an efficient and versatile route to construct functional materials, especially for the fabrication of novel and multifunctional materials, due to the collaborative strategy in the distinct constituent units. Meanwhile, the precise crystal architectures of organic cocrystals, with long-range order as well as free defects, offer the opportunity to unveil the structure-property and charge-transfer-property relationships, which are beneficial to provide some general rules in rational design and choice of functional materials. In this regard, an overview of organic cocrystals in terms of assembly, containing the intermolecular interactions and growth methods, two functionality-related factors including packing structure and charge-transfer nature, and those advanced and novel functionalities, is presented. An outlook of future research directions and challenges for organic cocrystal is also provided.

Exciton funneling in light-harvesting organic semiconductor microcrystals for wavelength-tunable lasers

Organic solid-state lasers are essential for various photonic applications, yet current-driven lasing remains a great challenge. Charge transfer (CT) complexes formed with p-/n-type organic semiconductors show great potential in electrically pumped lasers, but it is still difficult to achieve population inversion owing to substantial nonradiative loss from delocalized CT states. Here, we demonstrate the lasing action of CT complexes based on exciton funneling in p-type organic microcrystals with n-type doping. The CT complexes with narrow bandgap were locally formed and surrounded by the hosts with high-lying energy levels, which behave as artificial light-harvesting systems. Excitation light energy captured by the hosts was delivered to the CT complexes, functioning as exciton funnels to benefit lasing actions. The lasing wavelength of such composite microcrystals was further modulated by varying the degree of CT. The results offer a comprehensive understanding of exciton funneling in light-harvesting systems for the development of high-performance organic lasing devices.

Halogen Bonding: A Halogen-Centered Noncovalent Interaction Yet to Be Understood

In addition to the underlying basic concepts and early recognition of halogen bonding, this paper reviews the conflicting views that consistently appear in the area of noncovalent interactions and the ability of covalently bonded halogen atoms in molecules to participate in noncovalent interactions that contribute to packing in the solid-state. It may be relatively straightforward to identify Type-II halogen bonding between atoms using the conceptual framework of σ-hole theory, especially when the interaction is linear and is formed between the axial positive region (σ-hole) on the halogen in one monomer and a negative site on a second interacting monomer. A σ-hole is an electron density deficient region on the halogen atom X opposite to the R–X covalent bond, where R is the remainder part of the molecule. However, it is not trivial to do so when secondary interactions are involved as the directionality of the interaction is significantly affected. We show, by providing some specific examples, that halogen bonds do not always follow the strict Type-II topology, and the occurrence of Type-I and -III halogen-centered contacts in crystals is very difficult to predict. In many instances, Type-I halogen-centered contacts appear simultaneously with Type-II halogen bonds. We employed the Independent Gradient Model, a recently proposed electron density approach for probing strong and weak interactions in molecular domains, to show that this is a very useful tool in unraveling the chemistry of halogen-assisted noncovalent interactions, especially in the weak bonding regime. Wherever possible, we have attempted to connect some of these results with those reported previously. Though useful for studying interactions of reasonable strength, IUPAC’s proposed “less than the sum of the van der Waals radii” criterion should not always be assumed as a necessary and sufficient feature to reveal weakly bound interactions, since in many crystals the attractive interaction happens to occur between the midpoint of a bond, or the junction region, and a positive or negative site.

Choosing sides: unusual ultrafast charge transfer pathways in an asymmetric electron-accepting cyclophane that binds an electron donor

Photo-driven electron transfer is faster from an electron donor guest to the harder to reduce acceptor in an asymmetric cyclophane host.

Constructing functional molecular systems for solar energy conversion and quantum information science requires a fundamental understanding of electron transfer in donor–bridge–acceptor (D–B–A) systems as well as competitive reaction pathways in acceptor–donor–acceptor (A–D–A) and acceptor–donor–acceptor′ (A–D–A′) systems. Herein we present a supramolecular complex comprising a tetracationic cyclophane having both phenyl-extended viologen (ExV²⁺) and dipyridylthiazolothiazole (TTz²⁺) electron acceptors doubly-linked by means of two p-xylylene linkers (TTzExVBox⁴⁺), which readily incorporates a perylene (Per) guest in its cavity (Per ⊂ TTzExVBox⁴⁺) to establish an A–D–A′ system, in which the ExV²⁺ and TTz²⁺ units serve as competing electron acceptors with different reduction potentials. Photoexcitation of the Per guest yields both TTz⁺˙–Per⁺˙–ExV²⁺ and TTz²⁺–Per⁺˙–ExV⁺˙ in <1 ps, while back electron transfer in TTz²⁺–Per⁺˙–ExV⁺˙ proceeds via the unusual sequence TTz²⁺–Per⁺˙–ExV⁺˙ → TTz⁺˙–Per⁺˙–ExV²⁺ → TTz²⁺–Per–ExV²⁺. In addition, selective chemical reduction of TTz²⁺ gives Per ⊂ TTzExVBox³⁺˙, turning the complex into a D–B–A system in which photoexcitation of TTz⁺˙ results in the reaction sequence ²*TTz⁺˙–Per–ExV²⁺ → TTz²⁺–Per–ExV⁺˙ → TTz⁺˙–Per–ExV²⁺. Both reactions TTz²⁺–Per⁺˙–ExV⁺˙ → TTz⁺˙–Per⁺˙–ExV²⁺ and TTz²⁺–Per–ExV⁺˙ → TTz⁺˙–Per–ExV²⁺ occur with a (16 ± 1 ps)^–1 rate constant irrespective of whether the bridge molecule is Per⁺˙ or Per. These results are explained using the superexchange mechanism in which the ionic states of the perylene guest serve as virtual states in each case and demonstrate a novel supramolecular platform for studying the effects of bridge energetics within D–B–A systems.

Hybrids of Fullerenes and 2D Nanomaterials

Fullerene has a definite 0D closed-cage molecular structure composed of merely sp2-hybridized carbon atoms, enabling it to serve as an important building block that is useful for constructing supramolecular assemblies and micro/nanofunctional materials. Conversely, graphene has a 2D layered structure, possessing an exceptionally large specific surface area and high carrier mobility. Likewise, other emerging graphene-analogous 2D nanomaterials, such as graphitic carbon nitride (g-C3N4), transition-metal dichalcogenides (TMDs), hexagonal boron nitride (h-BN), and black phosphorus (BP), show unique electronic, physical, and chemical properties, which, however, exist only in the form of a monolayer and are typically anisotropic, limiting their applications. Upon hybridization with fullerenes, noncovalently or covalently, the physical/chemical properties of 2D nanomaterials can be tailored and, in most cases, improved, significantly extending their functionalities and applications. Here, an exhaustive review of all types of hybrids of fullerenes and 2D nanomaterials, such as graphene, g-C3N4, TMDs, h-BN, and BP, including their preparations, structures, properties, and applications, is presented. Finally, the prospects of fullerene-2D nanomaterial hybrids, especially the opportunity of creating unknown functional materials by means of hybridization, are envisioned.

Molecular assembly-induced charge transfer between a mixed (phthalocyaninato)(porphyrinato) yttrium triple-decker and a fullerene

A close interface of a mixed (phthalocyaninato)(porphyrinato) yttrium triple-decker and a fullerene in cocrystals affords stronger charge transfer than each individual.

Discovery of two types of new porphyrin–C70 co-crystals: influence of intermolecular contact on the inherent resistance

Two types of supramolecular aggregates based on C₇₀ were synthesised and their inherent resistances were analysed.

Materials nanoarchitectonics at two-dimensional liquid interfaces

Much attention has been paid to the synthesis of low-dimensional materials from small units such as functional molecules. Bottom-up approaches to create new low-dimensional materials with various functional units can be realized with the emerging concept of nanoarchitectonics. In this review article, we overview recent research progresses on materials nanoarchitectonics at two-dimensional liquid interfaces, which are dimensionally restricted media with some freedoms of molecular motion. Specific characteristics of molecular interactions and functions at liquid interfaces are briefly explained in the first parts. The following sections overview several topics on materials nanoarchitectonics at liquid interfaces, such as the preparation of two-dimensional metal-organic frameworks and covalent organic frameworks, and the fabrication of low-dimensional and specifically structured nanocarbons and their assemblies at liquid-liquid interfaces. Finally, interfacial nanoarchitectonics of biomaterials including the regulation of orientation and differentiation of living cells are explained. In the recent examples described in this review, various materials such as molecular machines, molecular receptors, block-copolymer, DNA origami, nanocarbon, phages, and stem cells were assembled at liquid interfaces by using various useful techniques. This review overviews techniques such as conventional Langmuir-Blodgett method, vortex Langmuir-Blodgett method, liquid-liquid interfacial precipitation, instructed assembly, and layer-by-layer assembly to give low-dimensional materials including nanowires, nanowhiskers, nanosheets, cubic objects, molecular patterns, supramolecular polymers, metal-organic frameworks and covalent organic frameworks. The nanoarchitecture materials can be used for various applications such as molecular recognition, sensors, photodetectors, supercapacitors, supramolecular differentiation, enzyme reactors, cell differentiation control, and hemodialysis.

Intermolecular packing and charge transfer in metallofullerene/porphyrin cocrystals

Charge transfer in metallofullerene/porphyrin cocrystals is revealed for the first time.

Understanding the affinity of bis-exTTF macrocyclic receptors towards fullerene recognition

Embracing [60]fullerene: Quantification of the C₆₀ affinity with a new series of exTTF macrocycles allows understanding the driving forces governing the supramolecular recognition upon increasing the alkyl ether chain size. Counterintuitively, an outside-ring complexation is found as the preferred arrangement over the expected inside-ring disposition.

Porphyrin Boxes

In order to fabricate efficient molecular photonic devices, it has been a long-held aspiration for chemists to understand and mimic natural light-harvesting complexes where a rapid and efficient transfer of excitation energy between chlorophyll pigments is observed. Synthetic porphyrins are attractive building blocks in this regard because of their rigid and planar geometry, high thermal and electronic stability, high molar extinction, small and tunable band gap, and tweakable optical as well as redox behavior. Owing to these fascinating properties, various types of porphyrin-based architectures have been reported utilizing both covalent and noncovalent approaches. However, it still remains a challenge to construct chemically robust, well-defined three-dimensional porphyrin cages which can be easily synthesized and yet suitable for useful applications both in solution as well as in solid state. Working on this idea, we recently synthesized box-shaped organic cages, which we called porphyrin boxes, by making use of dynamic covalent chemistry of imine condensation reaction between 4-connecting, square-shaped, tetraformylporphyrin and 3-connecting, triangular-shaped, triamine molecules. Various presynthetic, as well as postsynthetic modifications, can be carried out on porphyrin boxes including a variation of the alkyl chain length in their 3-connecting subunit, chemical functionalization, and metalation of the porphyrin core. This can remarkably tune their inherent properties, e.g., solubility, window size, volume, and polarity of the internal void. The porphyrin boxes can therefore be considered as a significant addition to the family of multiporphyrin-based architectures, and because of their chemical stability and shape persistency, the applications of porphyrin boxes expand beyond the photophysical properties of an artificial light-harvesting complex. Consequently, they have been exploited as porous organic cages, where their gas adsorption properties have been investigated. By incorporating them in a lipid bilayer membrane, an iodide selective synthetic ion channel has also been demonstrated. Further, we have explored electrocatalytic reduction of carbon dioxide using Fe(III) metalated porphyrin boxes. Additionally, the precise size and ease of metalation of porphyrin boxes allowed us to utilize them as premade building blocks for creating coordination-based hierarchical superstructures. Considering these developments, it may be worth combining the photophysical properties of porphyrin with the shape-persistent porous nature of porphyrin boxes to explore other novel applications. This Account summarizes our recent work on porphyrin boxes, starting with their design, structural features, and applications in different fields. We also try to provide scientific insight into the future opportunities that these amazing boxes have in store for exploring the still uncharted challenging domains in the field of supramolecular chemistry in a confined space.

Excitation-dependent electron exchange energy and electron transfer dynamics in a series of covalently tethered N,N-bis(4'-tert-butylbiphenyl-4-yl)aniline - [C60] fullerene dyads via varying π-conjugated spacers

Femtosecond time-resolved fluorescence and transient absorption studies are reported for three newly synthesized covalently linked N,N-bis(4'-tert-butylbiphenyl-4-yl)aniline (BBA) and pyrrolidinofullerenes (C60)-based donor-π conjugated bridge-acceptor dyads (D-B-A) as functions of the bridge length (7.1, 9.5 and 11.2 Å for Dyad-1, Dyad-2 and Dyad-3), dielectric constants of the medium and pump wavelengths. In polar solvent, ultrafast fluorescence quenching (kEET ≥ 2 × 1012 s-1) of the BBA moiety upon excitation of the BBA moiety (320 nm) is observed in the dyads and is assigned to a mechanism involving electron exchange energy transfer (EET) from 1BBA* to C60 followed by electron transfer from BBA to 1C60*. Cohesive rise and decay dynamics of conjugated BBA˙+-C60˙- anion pairs confirm the involvement of a distance independent adiabatic charge-separation (CS) process (kCS ≥ 2.2 × 1011 s-1) with near unity quantum efficiency (φCS ≥ 99.7%) and a distance-dependent non-adiabatic charge-recombination (CR) process [kCR ∼ (1010-108) s-1]. In contrast, excitation of the C60 moiety (λex = 430 to 700 nm) illustrates photoinduced electron transfer from BBA to 1C60*, involving non-adiabatic (diabatic) and distance-dependent CS (kCS in the range of 0.59-1.78 × 1011 s-1) with 98.86-99.6% (Dyad-3-Dyad-1) quantum efficiency and a CR process with kCR values [kCR ∼ (1010-108) s-1] up to three orders greater than kCS of the respective dyads. Both the processes, CS and CR, upon C60 excitation and the CR process upon BBA excitation show distance dependent rate constants with exponential factor β ≤ 0.5 Å-1, and electron transfer is concluded to occur through a covalently linked conjugated π bridge. Global and target analysis of fsTA data reveal the occurrence of two closely lying CS states, thermally hot (CShot) and thermally relaxed (CSeq) states, and two CR processes with two orders of different rate constants. Careful analysis of the kinetic and thermodynamic data allowed us to estimate the total reorganization energy and electronic coupling matrix (V), which decrease exponentially with distance. These novel features of the distance independent adiabatic CS process and the distance-dependent diabatic CR process upon donor excitation are due to extending the π-conjugation between BBA and C60. The demonstrated results may provide a benchmark in the design of light-harvesting molecular devices where ultrafast CS processes and long-lived CS states are essential requirements.

Ultralarge Nanosheets Fabricated by the Hierarchical Self-Assembly of Porphyrin-Ended Hyperbranched Poly (ether amine) (TPP-hPEA)

An ultralarge sheet with remarkable lateral dimensions of 10 µm × 10 µm-20 µm × 20 µm is fabricated by the hierarchical self-assembly of porphyrin-ended hyperbranched poly(ether amine) (tetraphenylporphyrin (TPP)-hPEA) in solution. The obtained TPP-hPEA amphiphiles can self-assemble from ultrathin single-layered nanosheets with a thickness of 4 nm to ultralarge multilayered nanosheets with thicknesses from 30 to 70 nm. The lateral dimensions increase from 2 × 2 µm to 5 × 5 µm, and eventually to 10 × 10 µm. In-situ dynamic light scattering and UV-vis spectroscopy studies suggest a hierarchical growth self-assembly mechanism with a self-assembly process that relies on π-π stacking. This 2D self-assembly method provides a significant potential guide for the preparation of ultralarge nanosheets in solution.

Fullerenes – how 25 years of charge transfer chemistry have shaped our understanding of (interfacial) interactions

Over 25 years research in charge transfer chemistry are highlighted in terms of interfacial interactions between fullerenes and porphyrins in electron donor–acceptor systems.