Nanohybrids from nanotubular J-aggregates and transparent silica nanoshells

Developing an off-on fluorescence sensor based on red copper nanoclusters wrapped by sulfhydryl and polymer double ligands for sensitive detection of N-acetyl-L-cysteine

N-acetyl-L-cysteine (NAC) as a class of thiols is commonly used in the treatment of lung diseases, detoxification and prevention of liver damage. In this paper, 4-mercaptobenzoic acid (4-MBA) coated and polyvinylpyrrolidone (PVP) attached copper nanoclusters (4-MBA@PVP-CuNCs) were successfully synthesized using a simple one-pot method with an absolute quantum yield of 10.98 %, and its synthetic conditions (like effects of single/double ligands and temperature) were studied intensively. Then Hg2+ could quench the fluorescence of the 4-MBA@PVP-CuNCs and its fluorescence was restored with the addition of NAC. Based on the above principles, an off-on switching system was established to detect NAC. That is, the 4-MBA@PVP-CuNCs-Hg probe was prepared by adding Hg2+ to switch off the fluorescence of the CuNCs by static quenching, and then NAC was added to switch on the fluorescence of the probe based on the chelation of NAC and Hg2+. Moreover, the effects of metal ion types and mercury ion doses for the probe construction were also further discussed. The method showed excellent linearity in the range of 0.05-1.25 µM and low detection limit of 16 nM. Meanwhile, good recoveries in real urine, tablets and pellets were observed, which proved the reliability of the method and provided a convenient, fast and sensitive method for NAC detection.

Bright and Fast Emission from Robust Supramolecular J-Aggregate Nanostructures through Silica-Encapsulation

We introduce a two-step silica-encapsulation procedure to optimize both the optical efficiency and structural robustness of 5,5',6,6'-tetrachloro-1,1'-diethyl-3,3'-di(4-sulfobutyl)-benzimidazolocarbocyanine (TDBC), a two-dimensional sheet-like J-aggregate. We report a fluorescence quantum yield of ∼98%, the highest quantum yield recorded for any J-aggregate structure at room temperature, and a fast, emissive lifetime of 234 ps. Silica, as an encapsulating matrix, provides optical transparency, chemical inertness, and robustness to dilution, while rigidifying the J-aggregate structure. Our in situ encapsulation process preserves the excitonic structure in TDBC J-aggregates, maintaining their light absorption and emission properties. The homogeneous silica coating has an average thickness of 0.5-1 nm around J-aggregate sheets. Silica encapsulation permits extensive dilutions of J-aggregates without significant disintegration into monomers. The narrow absorbance and emission line widths exhibit further narrowing upon cooling to 79 K, which is consistent with J-type coupling in the encapsulated aggregates. This silica TDBC J-aggregate construct signifies (1) a bright, fast, and robust fluorophore system, (2) a platform for further manipulation of J-aggregates as building blocks for integration with other optical materials and structures, and (3) a system for fundamental studies of exciton delocalization, transport, and emission dynamics within a rigid matrix.

Molecular and Supramolecular Materials: From Light-Harvesting to Quantum Information Science and Technology

The past two decades have witnessed immense advances in quantum information technology (QIT), benefited by advances in physics, chemistry, biology, and materials science and engineering. It is intriguing to consider whether these diverse molecular and supramolecular structures and materials, partially inspired by quantum effects as observed in sophisticated biological systems such as light-harvesting complexes in photosynthesis and the magnetic compass of migratory birds, might play a role in future QIT. If so, how? Herein, we review materials and specify the relationship between structures and quantum properties, and we identify the challenges and limitations that have restricted the intersection of QIT and chemical materials. Examples are broken down into two categories: materials for quantum sensing where nonclassical function is observed on the molecular scale and systems where nonclassical phenomena are present due to intermolecular interactions. We discuss challenges for materials chemistry and make comparisons to related systems found in nature. We conclude that if chemical materials become relevant for QIT, they will enable quite new kinds of properties and functions.

Mussel-Inspired Surface Coating to Stabilize and Functionalize Supramolecular J-Aggregate Nanotubes Composed of Amphiphilic Cyanine Dyes

We report a mussel-inspired strategy of polydopamine (PDA) coating to stabilize and functionalize J-aggregate nanotubes (NTs) formed by supramolecular self-assembly of an amphiphilic cyanine dye called C8S3 in aqueous media. Optimization of the coating condition by changing the incubation time in a slightly basic media of dopamine with different concentrations leads to conformal wrapping of the PDA layer with controllable thickness on the surface of the NTs. Compared to noncoated pristine C8S3 NTs, these PDA-coated NTs show enhanced stability against dilution, heating, and photobleaching. Moreover, the PDA layer wrapping around the NTs serves as an adhesive for the adsorption of a variety of metal ions and electroless deposition of the metal nanoparticles. Such stabilized and functionalized NT composites may offer a robust synthetic J-aggregate system to mimic the structure and function of light-harvesting complexes and reaction centers in photosynthetic systems.

Frenkel excitons in heat-stressed supramolecular nanocomposites enabled by tunable cage-like scaffolding

Delocalized Frenkel excitons-coherently shared excitations among chromophores-are responsible for the remarkable efficiency of supramolecular light-harvesting assemblies within photosynthetic organisms. The translation of nature's design principles to applications in optoelectronic devices has been limited by the fragility of the supramolecular structures used and the delicate nature of Frenkel excitons, particularly under mildly changing solvent conditions and elevated temperatures and upon deposition onto solid substrates. Here, we overcome those functionalization barriers through composition of stable supramolecular light-harvesting nanotubes enabled by tunable (~4.3-4.9 nm), uniform (±0.3 nm) cage-like scaffolds. High-resolution cryogenic electron microscopy, combined with scanning electron microscopy, broadband femtosecond transient absorption spectroscopy and near-field scanning optical microscopy revealed that excitons within the cage-like scaffolds are robust, even under extreme heat stress, and control over nanocomposite dimensions is maintained on solid substrates. Our bio-inspired nanocomposites provide a general framework for the development of next-generation organic devices made from stable supramolecular materials.

Individual tubular J-aggregates stabilized and stiffened by silica encapsulation

Amphiphilic cyanine dyes in aqueous solution self-assemble into J-aggregates with diverse structures. In particular, the dye 3,3′-bis(3-sulfopropyl)-5,5′,6,6′-tetrachloro-1,1′-dioctylbenzimida-carbo-cyanine (C8S3) forms micrometer long double walled tubular J-aggregates with a uniform outer diameter of 13 ± 0.5 nm. Interestingly, these J-aggregates exhibit strong exciton delocalization and migration, similar to natural light harvesting systems. However, their structural integrity and hence their optical properties are very sensitive to their chemical environment as well as to mechanical deformation, rendering detailed studies on individual tubular J-aggregates difficult. We addressed this issue and examined a previously published route for their chemical and mechanical stabilization by in situ synthesis of a silica coating that leaves their absorbance and emission unaltered in solution. Here, we demonstrate that the silica shell with a thickness of a few nanometers is able to stabilize the tubular J-aggregates of C8S3 against changes of pH of solutions down to values where pure aggregates are oxidized, against drying under ambient conditions, and even against the vacuum conditions within an electron microscope. Dried silica–covered aggregates are brittle, as demonstrated by manipulation with a scanning force microscope on a surface. Transmission electron microscope images confirm that the thickness of the coatings is homogeneous and uniform with a thickness of less than 5 nm; scanning TEM energy dispersive X-ray spectroscopy confirms the chemical composition of the shell as SiO2; and electron energy loss spectra could be recorded across a single freely suspended aggregate. Such a silica shell may not only serve for stabilization but also could be the base for further functionalization of the aggregates by either chemical attachment of other units on top of the shell or by inclusion during the synthesis.

Shortwave Infrared Imaging with J-Aggregates Stabilized in Hollow Mesoporous Silica Nanoparticles

Tissue is translucent to shortwave infrared (SWIR) light, rendering optical imaging superior in this region. However, the widespread use of optical SWIR imaging has been limited, in part, by the lack of bright, biocompatible contrast agents that absorb and emit light above 1000 nm. J-Aggregation offers a means to transform stable, near-infrared (NIR) fluorophores into red-shifted SWIR contrast agents. Here we demonstrate that J-aggregates of NIR fluorophore IR-140 can be prepared inside hollow mesoporous silica nanoparticles (HMSNs) to result in nanomaterials that absorb and emit SWIR light. The J-aggregates inside PEGylated HMSNs are stable for multiple weeks in buffer and enable high resolution imaging in vivo with 980 nm excitation.

Silver iodide nanowires grown within tubular J-aggregates

Silver iodide nanowires have been grown within tubular J-aggregates of the cyanine dye 3,3'-bis(2-sulfopropyl)-5,5',6,6'-tetrachloro-1,1'-dioctylbenzimida-carbo-cyanine (C8S3) from aqueous AgNO₃ solutions. Crystal structure analysis by selected area electron diffraction (SAED), high resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray spectroscopy (EDXS) of single nanowires revealed that they are of silver iodide (AgI), while previously they were presumed to be of metallic silver. Iodine has not been added intentionally, but it is a remnant from the chemical synthesis of the dye and present in a dye:iodine ratio of almost 2:1, as revealed by inductively coupled plasma mass spectrometry (ICP-MS). The AgI wires grow as single crystals with lengths of several 10-100 nm and width of 6.5 ± 0.5 nm. The width and the orientation of the crystal relative to the aggregate axis are defined by the tubular structure of the templating dye aggregate. Caused by the nucleation at the tube wall the main growth is not along the usually preferred [0 0 0 1] direction but along the extension of the basal plane, which is furthermore tilted by an angle of 6° ± 2° against the main axis of the aggregate. This self-assembled system represents an organic-inorganic hybrid system with a well-defined semiconductor nanowire, AgI, that is strictly oriented with respect to the aggregated phase of conjugated molecules.

Observation of Vibronic-Coupling-Mediated Energy Transfer in Light-Harvesting Nanotubes Stabilized in a Solid-State Matrix

Ultrafast vibrational spectroscopy is employed to obtain real-time structural information on energy transport in double-walled light-harvesting nanotubes at room temperature, stabilized in a host matrix to mimic the rigid scaffolds of natural light-harvesting systems. We observe evidence of a low-frequency vibrational mode at 315 cm^-1, which transfers excitons from the outer wall of the nanotubes to a crossing point through which energy transfer to the inner wall can occur. This mode is furthermore absent in solution phase. Importantly, the coherence of this mode is not transferred to the inner wall upon energy transfer and is only present on the outer wall's excited-state energy surface, highlighting that complete energy transfer between the outer and inner walls does not take place. Isolation of the individual walls of the nanotubes provides evidence that this mode corresponds to a supramolecular motion of the nanotubes. Our results emphasize the importance of the solid-state environment in modulating vibronic coupling and directing energy transfer in molecular light-harvesting systems.

Bioinspired Silicification Reveals Structural Detail in Self-Assembled Peptide Cages

Understanding how molecules in self-assembled soft-matter nanostructures are organized is essential for improving the design of next-generation nanomaterials. Imaging these assemblies can be challenging and usually requires processing, e.g., staining or embedding, which can damage or obscure features. An alternative is to use bioinspired mineralization, mimicking how certain organisms use biomolecules to template mineral formation. Previously, we have reported the design and characterization of Self-Assembled peptide caGEs (SAGEs) formed from de novo peptide building blocks. In SAGEs, two complementary, 3-fold symmetric, peptide hubs combine to form a hexagonal lattice, which curves and closes to form SAGE nanoparticles. As hexagons alone cannot tile onto spheres, the network must also incorporate nonhexagonal shapes. While the hexagonal ultrastructure of the SAGEs has been imaged, these defects have not been observed. Here, we show that positively charged SAGEs biotemplate a thin, protective silica coating. Electron microscopy shows that these SiO2-SAGEs do not collapse, but maintain their 3D shape when dried. Atomic force microscopy reveals a network of hexagonal and irregular features on the SiO2-SAGE surface. The dimensions of these (7.2 nm ± 1.4 nm across, internal angles 119.8° ± 26.1°) are in accord with the designed SAGE network and with coarse-grained modeling of the SAGE assembly. The SiO2-SAGEs are permeable to small molecules (<2 nm), but not to larger biomolecules (>6 nm). Thus, bioinspired silicification offers a mild technique that preserves soft-matter nanoparticles for imaging, revealing structural details <10 nm in size, while also maintaining desirable properties, such as permeability to small molecules.

Fluorescent Cyanine Dye J-Aggregates in the Fluorous Phase

We present a perfluorocarbon-hydrocarbon amphiphilic cyanine dye that J-aggregates in fluorous solvent. J-Aggregation is a special type of fluorophore aggregation, affording enhanced photophysical properties. Cyanine dyes are excellent J-aggregators in water but, until now, cyanine J-aggregates have not been translated to nonaqueous media. The fluorous phase J-aggregate displays enhanced photostability and processability compared to analogous aqueous aggregates.

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.