Light-Harvesting Nanotubes Formed by Supramolecular Assembly of Aromatic Oligophosphates

Interfacial self-assembly of a chiral pyrene exciplex into a superhelix with enhanced circularly polarized luminescence

We found that the interfacially confined self-assembly of pyrene and phenanthrene glutamides can form strong exciplexes and amorphous superhelices, which show intensity-enhanced and sign-inverted CPL activity with improved quantum yield compared to a pyrene excimer. This work unveils the predominant role of supramolecular nanostructures over molecular configurations on CPL performance.

Supramolecular assembly of pyrene-DNA conjugates: influence of pyrene substitution pattern and implications for artificial LHCs

The supramolecular self-assembly of pyrene-DNA conjugates into nanostructures is presented. DNA functionalized with different types of pyrene isomers at the 3'-end self-assemble into nano-objects. The shape of the nanostructures is influenced by the type of pyrene isomer appended to the DNA. Multilamellar vesicles are observed with the 1,6- and 1,8-isomers, whereas conjugates of the 2,7-isomer exclusively assemble into spherical nanoparticles. Self-assembled nano-spheres obtained with the 2,7-dialkynyl pyrene isomer were used for the construction of an artificial light-harvesting complex (LHC) in combination with Cy3 as the energy acceptor.

Directed Gradients in the Excited-State Energy Landscape of Poly(3-hexylthiophene) Nanofibers

Funneling excitation energy toward lower energy excited states is a key concept in photosynthesis, which is often realized with at most two chemically different types of pigment molecules. However, current synthetic approaches to establish energy funnels, or gradients, typically rely on Förster-type energy-transfer cascades along many chemically different molecules. Here, we demonstrate an elegant concept for a gradient in the excited-state energy landscape along micrometer-long supramolecular nanofibers based on the conjugated polymer poly(3-hexylthiophene), P3HT, as the single component. Precisely aligned P3HT nanofibers within a supramolecular superstructure are prepared by solution processing involving an efficient supramolecular nucleating agent. Employing hyperspectral imaging, we find that the lowest-energy exciton band edge continuously shifts to lower energies along the nanofibers' growth direction. We attribute this directed excited-state energy gradient to defect fractionation during nanofiber growth. Our concept provides guidelines for the design of supramolecular structures with an intrinsic energy gradient for nanophotonic applications.

Self-assembled supramolecular artificial light-harvesting nanosystems: construction, modulation, and applications

Artificial light-harvesting systems, an elegant way to capture, transfer and utilize solar energy, have attracted great attention in recent years. As the primary step of natural photosynthesis, the principle of light-harvesting systems has been intensively investigated, which is further employed for artificial construction of such systems. Supramolecular self-assembly is one of the feasible methods for building artificial light-harvesting systems, which also offers an advantageous pathway for improving light-harvesting efficiency. Many artificial light-harvesting systems based on supramolecular self-assembly have been successfully constructed at the nanoscale with extremely high donor/acceptor ratios, energy transfer efficiency and the antenna effect, which manifests that self-assembled supramolecular nanosystems are indeed a viable way for constructing efficient light-harvesting systems. Non-covalent interactions of supramolecular self-assembly provide diverse approaches to improve the efficiency of artificial light-harvesting systems. In this review, we summarize the recent advances in artificial light-harvesting systems based on self-assembled supramolecular nanosystems. The construction, modulation, and applications of self-assembled supramolecular light-harvesting systems are presented, and the corresponding mechanisms, research prospects and challenges are also briefly highlighted and discussed.

Porphyrin nanotubes based on a hydrogen-bonded organic framework

Tubular structures offer a wide variety of applications; therefore, designing such materials with distinct dimensions is highly desirable yet challenging. In the current report, we have demonstrated the synthesis of a one-dimensional (1D) tubular assembly comprising porphyrin nanoring subunits. The porphyrin nanoring (PNR) 2 bearing ester groups was synthesized via Pt-mediated cyclization and then hydrolyzed to obtain PNR 3 with carboxylic groups. Under optimized conditions, porphyrin nanotubes (PNTs) were formed through hydrogen bonding between the carboxylic groups of 3. The morphology investigated by both SEM and TEM displayed well-defined arrays of nanotube bundles up to several micrometers long. Small crystals of PNTs were obtained by heating a solution of 3 in DMSO. High-resolution transmission electron microscopy (HR-TEM) accompanied by selected-area electron diffraction (SAED) exhibited a line of diffractions with d-spacing values of 6.17, 3.08, 2.07, and 1.57 Å. The miller indices of these diffractions could be assigned as 300, 600, 900, and 1200, respectively, suggesting that an ordered structure of 1D PNTs has been formed.

Artificial Light-Harvesting System with White-Light Emission in a Bicontinuous Ionic Medium

Artificial light-harvesting systems (ALHSs), which are closely related to Förster resonance energy transfer (FRET), are among the most attractive scientific topics during the past few decades. Specifically, binary ALHSs that are composed of a fluid donor and acceptor have a simplified composition and high number density of the donor units. However, largely due to the difficulty in obtaining a fluid donor, investigation of these systems is still quite limited, especially for the ionic systems. Herein, we report a new type of binary ALHS using an ionic naphthalimide (NPI) derivative as a donor, which shows greatly improved photoluminescence for its bicontinuous liquid structure. When blending with an acceptor such as rhodamine 6G or trans-4-[4-(dimethylamino)styryl]-methylpyridinium iodide, efficient FRET was confirmed by both experimental results and molecular dynamics simulations, with an energy transfer efficiency up to ∼90%. Tunable color, including white-light emission, was achieved by tuning the acceptor/donor ratio, opening the door for a variety of applications such as light-emitting diodes and photoluminescent inks.

Highly Efficient Artificial Light-Harvesting Systems Constructed in an Aqueous Solution Based on Twisted Cucurbit[14]Uril

Relying on the supramolecular self-assembly of twisted cucurbit[14]urils (tQ[14]), anthracene derivatives (ADPy), Nile red (NiR), and rhodamine B (RB), highly efficient light-harvesting systems have been successfully designed in an aqueous medium. The addition of tQ[14] causes ADPy to aggregate through supramolecular self-assembly to form a supramolecular polymer (ADPy@tQ[14]) with excellent aggregation-induced fluorescence and an interesting spherical external morphology, making it a remarkable energy donor. Consequently, efficient energy-transfer processes have occurred between ADPy@tQ[14] assembly and NiR and RB, which both serve as effective energy acceptors while being loaded onto ADPy@tQ[14]. In the case of NiR, the energy-transfer efficiency is up to 72.45%, and the antenna effect is near 55.4 at a donor/acceptor ratio of 100:1, making it close to the light-harvesting systems in nature. As a result, effective water-soluble artificial light-harvesting systems are showing enormous prospective as versatile platforms for simulating photosynthesis.

Complex DNA Architectonics─Self-Assembly of Amphiphilic Oligonucleotides into Ribbons, Vesicles, and Asterosomes

The precise arrangement of structural subunits is a key factor for the proper shape and function of natural and artificial supramolecular assemblies. In DNA nanotechnology, the geometrically well-defined double-stranded DNA scaffold serves as an element of spatial control for the precise arrangement of functional groups. Here, we describe the supramolecular assembly of chemically modified DNA hybrids into diverse types of architectures. An amphiphilic DNA duplex serves as the sole structural building element of the nanosized supramolecular structures. The morphology of the assemblies is governed by a single subunit of the building block. The chemical nature of this subunit, i.e., polyethylene glycols of different chain length or a carbohydrate moiety, exerts a dramatic influence on the architecture of the assemblies. Cryo-electron microscopy revealed the arrangement of the individual DNA duplexes within the different constructs. Thus, the morphology changes from vesicles to ribbons with increasing length of a linear polyethylene glycol. Astoundingly, attachment of a N-acetylgalactosamine carbohydrate to the DNA duplex moiety produces an unprecedented type of star-shaped architecture. The novel DNA architectures presented herein imply an extension of the current concept of DNA materials and shed new light on the fast-growing field of DNA nanotechnology.

Photo-modulation of supramolecular polymorphism in the self-assembly of a scissor-shaped azobenzene dyad into nanotoroids and fibers

Recent advances in the research field of supramolecularly engineered dye aggregates have enabled the design of simple one-dimensional stacks such as fibers and of closed structures such as nanotoroids (nanorings). More complex and advanced supramolecular systems could potentially be designed using a molecule that is able to provide either of these distinct nanostructures under different conditions. In this study, we introduced bulky but strongly aggregating cholesterol units to a scissor-shaped azobenzene dyad framework, which affords either nanotoroids, nanotubes, or 1D fibers, depending on the substituents. This new dyad with two trans-azobenzene arms shows supramolecular polymorphism in its temperature-controlled self-assembly, leading to not only oligomeric nanotoroids as kinetic products, but also to one-dimensional fibers as thermodynamic products. This supramolecular polymorphism can also be achieved via photo-triggered self-assembly, i.e., irradiation of a monomeric solution of the dyad with two cis-azobenzene arms using strong visible light leads to the preferential formation of nanotoroids, whereas irradiation with weak visible light leads to the predominant formation of 1D fibers. This is the first example of a successful light-induced modulation of supramolecular polymorphism to produce distinctly nanostructured aggregates under isothermal conditions.

Inverted Circularly Polarized Luminescence Behavior Induced by Helical Nanofibers through Chiral Co-Assembly from Achiral Liquid Crystal Polymers and Chiral Inducers

Chiral supramolecular assembly can provide a powerful strategy for developing circularly polarized luminescence (CPL)-active materials by forming helices or superhelices into single or multiple components. Herein, we chose three achiral liquid crystal polymers (LC-P1/P2/P3) and chiral binaphthyl-based inducers (R/S-M) with anchored dihedral angles to construct chiral co-assemblies and explore the induced CPL behavior from pyrenyl (Py) emitters in achiral LC polymers through the regulation of helical nanofibers during the supramolecular co-assembly process. Most interestingly, chiral co-assembly (R/S-M)_0.1-(P3)_0.9 emitted an inverted blue-colored CPL signal during thermal annealing treatment at the glass transition temperature due to the flexible main chain of the LC polymer (LC-P3). The strongest blue-colored CPL emission for the (R/S-M)_0.1-(P3)_0.9 spin-coated film (λ_em = 455 nm, |g_em| = 6.47 × 10^-2, Φ_F = 48.5%) could be detected by using thermal annealing treatment at 105 °C.

Folding of phosphodiester-linked donor–acceptor oligomers into supramolecular nanotubes in water

Water soluble foldamers, synthesized by DNA synthesis with dialkoxynaphthalene and naphthalene-tetracarboxylic diimide blocks, formed supramolecular nanotubes in water.

Soft-Matter Nanotubes: A Platform for Diverse Functions and Applications

Self-assembled organic nanotubes made of single or multiple molecular components can be classified into soft-matter nanotubes (SMNTs) by contrast with hard-matter nanotubes, such as carbon and other inorganic nanotubes. To date, diverse self-assembly processes and elaborate template procedures using rationally designed organic molecules have produced suitable tubular architectures with definite dimensions, structural complexity, and hierarchy for expected functions and applications. Herein, we comprehensively discuss every functions and possible applications of a wide range of SMNTs as bulk materials or single components. This Review highlights valuable contributions mainly in the past decade. Fifteen different families of SMNTs are discussed from the viewpoints of chemical, physical, biological, and medical applications, as well as action fields (e.g., interior, wall, exterior, whole structure, and ensemble of nanotubes). Chemical applications of the SMNTs are associated with encapsulating materials and sensors. SMNTs also behave, while sometimes undergoing morphological transformation, as a catalyst, template, liquid crystal, hydro-/organogel, superhydrophobic surface, and micron size engine. Physical functions pertain to ferro-/piezoelectricity and energy migration/storage, leading to the applications to electrodes or supercapacitors, and mechanical reinforcement. Biological functions involve artificial chaperone, transmembrane transport, nanochannels, and channel reactors. Finally, medical functions range over drug delivery, nonviral gene transfer vector, and virus trap.

Amphiphilic anthanthrene trimers that exfoliate graphite and individualize single wall carbon nanotubes

A phosphodiester-linked dialkynyl substituted anthanthrene trimer (1) has been designed and synthesized. Its graphene ribbon like structure is expected to facilitate interactions with nanographene (NG) and single wall carbon nanotubes (SWCNT) to yield novel and stable carbon-based nanomaterials. Interactions with trimer 1 lead to exfoliation of NG and to the individualization of SWCNTs. Phosphate groups, in general, and their negative charges, in particular, render the resulting nanomaterials soluble in ethanol, which is ecologically favourable over DMF required for the processing of pristine NG or SWCNTs. The newly formed nanomaterials were probed by complementary spectroscopic and microscopic techniques. Of particular importance were transient absorption and fluorescence excitation measurements, which revealed an efficient energy transfer within the carbon-based nanomaterials.

Control of helical chirality in supramolecular chromophore-DNA architectures

Four different d- and l-configured chromophore-2'-deoxyuridine conjugates were applied to elucidate the helical chirality of their non-covalent assemblies along the d- and l-configured DNA templates by optical spectroscopy. There is no configuration-selective recognition between these nucleosides and the DNA templates. The helicity of the DNA assemblies is either controlled by the configuration of the DNA template or by the nucleoside configuration.

Ultrafast dynamics in polycyclic aromatic hydrocarbons: the key case of conical intersections at higher excited states and their role in the photophysics of phenanthrene monomer

Proper interpretation of phenanthrene's and similar PAHs’ photocycle relies on two higher excited state relaxations due to the simultaneous presence of non-adiabatic and adiabatic transitions.

Allosteric Self-Assembly of Coordinating Terthiophene Amphiphile for Triggered Light Harvesting

Allosteric regulation is extensively employed by nature to achieve functional control of protein or deoxyribonucleic acid through triggered conformational change at a remote site. We report that a similar strategy can be utilized in artificial self-assembly to control the self-assembled structure and its function. We show that on binding of metal ions to the headgroup of an amphiphile TTC4L, the conformational change may lead to change of the dipole orientation of the energy donor at the chain end. This on the one hand leads to a drastically different self-assembled structure; on the other hand, it enables light harvesting between the donor-acceptor. Because the Forster resonance fluorescence transfer efficiency is gated by metal ions, controlling the feeding of metal ions allows switching on and off of light harvesting. We expect that using allosteric self-assembly, we will be able to create abundant structures with distinct function from limited molecules, which show prominent potential for the postorganic modification of the structure and function of self-assembled materials.

Artificial light-harvesting supramolecular polymeric nanoparticles formed by pillar[5]arene-based host-guest interaction

Artificial light-harvesting nanoparticles were prepared from supramolecular polymers comprised of pillar[5]arene with anthracene-derived donors and acceptors through host-guest interactions. The resulting water-dispersible nanoparticles displayed efficient energy transfer and excellent light harvesting ability in part because the steric bulk of pillar[5]arene suppressed the self-quenching of the chromophores.

Successive energy transfer within multiple photosensitizers assembled in a hexameric hemoprotein scaffold

An assembly of multiple photosensitizers is demonstrated by development of a hexameric hemoprotein (HTHP) scaffold as a light harvesting model to replicate the successive energy transfer occuring within photosensitizer assemblies of natural systems. In our model, six zinc protoporphyrin IX (ZnPP) molecules are arrayed at the heme binding site of HTHP by supramolecular interactions and five fluorescein (Flu) molecules and one Texas Red (Tex) molecule as donor and acceptor photosensitizers, respectively, are attached to the HTHP protein surface with covalent linkages. The flow of excited energy from photoexcited Flu to Tex occurs via two pathways: direct energy transfer from Flu to Tex (path 1) and energy transfer via ZnPP (path 2). Steady state and time-resolved fluorescence measurements reveal that the energy transfer ratio of these pathways (path 1 : path 2) is 39 : 61. These findings indicate that the excited energy originating at five Flu and six ZnPP molecules is collected at one Tex molecule as a funnel-like bottom for light harvesting. The present system using the hexameric hemoprotein scaffold is a promising candidate for construction of an artificial light harvesting system having multiple photosensitizers to promote efficient use of solar energy.

Highly Efficient Artificial Light-Harvesting Systems Constructed in Aqueous Solution Based on Supramolecular Self-Assembly

Highly efficient light-harvesting systems were successfully fabricated in aqueous solution based on the supramolecular self-assembly of a water-soluble pillar[6]arene (WP6), a salicylaldehyde azine derivative (G), and two different fluorescence dyes, Nile Red (NiR) or Eosin Y (ESY). The WP6-G supramolecular assembly exhibits remarkably improved aggregation-induced emission enhancement and acts as a donor for the artificial light-harvesting system, and NiR or ESY, which are loaded within the WP6-G assembly, act as acceptors. An efficient energy-transfer process takes place from the WP6-G assembly not only to NiR but also to ESY for these two different systems. Furthermore, both of the WP6-G-NiR and WP6-G-ESY systems show an ultrahigh antenna effect at a high donor/acceptor ratio.

Water induced morphological transformation of a poly(aryl ether) dendron amphiphile: helical fibers to nanorods, as light-harvesting antenna systems

Self-assembly of suitable molecular building blocks is an efficient and convenient approach to generate nanomaterials with various morphologies and functions. Moreover, understanding the nature of molecules and controlling factors of their self-assembly process is crucial in fundamental aspects of molecular self-assembly which provide insights into the design of new assemblies with functional nano-architectures. To this end, the present study reports water induced self-assembled multifaceted morphology formation and the plausible pathway of the morphology transformation of a single poly(aryl ether) dendron amphiphile 1(D). In THF, 1(D) self-assembles into helical fibers. However, with an increase in the water fraction in its THF solution, the morphology changes to nanorods through an intermediate scroll-up pathway of exfoliated fibers. The nanorod formation and transformation of 1(D) are investigated using various microscopy and spectroscopy techniques, which indicate that it has highly ordered multilayered arrays of 1(D) molecules. Finally, these multilayered arrays of 1(D) nanorods are exploited for constructing a model light-harvesting system via the incorporation of small quantities of two newly designed BODIPY based molecules as energy acceptors and 1(D) as an antenna chromophore.

High definition polyphosphoesters: between nucleic acids and plastics

Nucleic acids and synthetic polyphosphoester materials have been distinct fields – this review shows how these areas now comprise a continuum.

Self-assembly of a redox-active bolaamphiphile into supramolecular vesicles

Self-assembly of a redox-active bolaamphiphile leads to the formation of narrow-bandgap supramolecular vesicles.

A Supramolecular Artificial Light-Harvesting System with an Ultrahigh Antenna Effect

An efficient artificial light-harvesting system is fabricated from a cyclic polysaccharide, sulfato-β-cyclodextrin (SCD); an aggregation-induced emission molecule, an oligo(phenylenevinylene) derivative (OPV-I); and a fluorescent dye, nile red (NiR), via noncovalent interactions in an aqueous solution. In this system, the OPV-I/SCD supramolecular assembly acts as a donor, and NiR that is loaded into the OPV-I/SCD assembly acts as an acceptor. Significantly, an efficient energy-transfer process occurs between the OPV-I/SCD assembly and the loaded NiR, leading to an extremely high antenna effect.

Silica Mineralization of DNA-Inspired 1D and 2D Supramolecular Polymers

The preparation of hybrid materials from supramolecular polymers through the sol‐gel process is presented. Supramolecular polymers are assembled from phosphodiester‐linked pyrene oligomers and act as water‐soluble one‐ or two‐dimensional templates for silicification. The fibrillary and planar morphologies of the assemblies, as well as the excitonic interactions between the chromophores, remain unaffected by the silicification process.

Enhancement of the photocatalytic activity of rhenium(i) complexes by encapsulation in light-harvesting soft nanotubes

The photocatalytic activity of a Re(i) complex encapsulated in dye-assembled nanotubes functioning as light-harvesting antennae was superior to that of a free Re(i) complex in bulk.

Solution-phase synthesis of 1D tubular polymers via preorganization–polymerization

Tubular polymers are synthesized by a preorganization–polymerization method in aqueous medium.