H-Aggregates of Oligophenyleneethynylene (OPE)-BODIPY Systems in Water: Guest Size-Dependent Encapsulation Mechanism and Co-aggregate Morphology

Keeping the chromophores crossed: evidence for null exciton splitting

Fundamental understanding of the supramolecular assemblies of organic chromophores and the development of design strategies have seen endless ripples of interest owing to their exciting photophysical properties and optoelectronic applications. The independent discovery of dye aggregates by Jelley and Scheibe was the commencement of the remarkable advancement in the field of aggregate photophysics. Subsequent research warranted an exceptional model for defining the exciton interactions in aggregates, proposed by Davydov, Kasha and co-workers, independently, based on the long-range Coulombic coupling. Fascinatingly, the orthogonally cross-stacked molecular transition dipole arrangement was foretold by Kasha to possess null exciton interaction leading to spectroscopically uncoupled molecular assembly, which lacked an experimental signature for decades. There have been several attempts to identify and probe atypical molecular aggregates for decoding their optical behaviour. Herein, we discuss the recent efforts in experimentally verifying the unusual exciton interactions supported with quantum chemical computations, primarily focusing on the less explored null exciton splitting. Exciton engineering can be realized through synthetic modifications that can additionally offer control over the assorted non-covalent interactions for orchestrating precise supramolecular assembly, along with molecular editing. The task of attaining a minimal excitonic coupling through an orthogonally cross-stacked crystalline architecture envisaged to offer a monomer-like optical behaviour was first reported in 1,7-dibromoperylene-3,4,9,10-tetracarboxylic tetrabutylester (PTE-Br2). The attempt to stitch molecules covalently in an orthogonal fashion to possess null excitonic character culminated in a spiro-conjugated perylenediimide dimer exhibiting a monomer-like spectroscopic signature. The computational and experimental efforts to map the emergent properties of the cross-stacked architecture are also discussed here. Using the null aggregates formed by the interference effects between CT-mediated and Coulombic couplings in the molecular array is another strategy for achieving monomer-like spectroscopic properties in molecular assemblies. Moreover, identifying supramolecular assemblies with precise angle-dependent properties can have implications in functional material design, and this review can provide insights into the uncharted realm of null exciton splitting.

Unadulterated BODIPY nanoparticles as light driven antibacterial agents for treating bacterial infections and promoting wound healing

Antimicrobial photodynamic therapy (aPDT) is an effective strategy to eliminate bacteria without inducing bacterial resistance. As typical aPDT photosensitizers, most of boron-dipyrromethene (BODIPY) are hydrophobic, and nanometerization is imperative to render them dispersible in physiological media. Recently, carrier-free nanoparticles (NPs) are formed via the self-assembly of BODIPYs without the help of any surfactants or auxiliaries, arousing people's interest. So as to fabricate carrier-free NPs, BODIPYs usually need to be derived into dimers, trimers, or amphiphiles through complex reactions. Few unadulterated NPs were obtained from BODIPYs with precise structures. Herein, BNP1-BNP3 were synthesized by the self-assembly of BODIPY, which showed excellent anti-Staphylococcus aureus ability. Among them, BNP2 could effectively fight bacterial infections and promote wound healing in vivo.

J-aggregation strategy of organic dyes for near-infrared bioimaging and fluorescent image-guided phototherapy

With the continuous development of organic materials for optoelectronic devices and biological applications, J-aggregation has attracted a great deal of interest in both dye chemistry and supramolecular chemistry. Except for the characteristic red-shifted absorption and emission, such ordered head-to-tail stacked structures may be accompanied by special properties such as enhanced absorption, narrowed spectral bandwidth, improved photothermal and photodynamic properties, aggregation-induced emission enhancement (AIEE) phenomenon, and so forth. These excellent properties add great potential to J-aggregates for optical imaging and phototherapy in the near-infrared (NIR) region. Despite decades of development, the challenge of rationally designing the molecular structure to adjust intermolecular forces to induce J-aggregation of organic dyes remains significant. In this review, we discuss the formation of J-aggregates in terms of intermolecular interactions and summarize some recent studies on J-aggregation dyes for NIR imaging and phototherapy, to provide a clear direction and reference for designing J-aggregates of near-infrared organic dyes to better enable biological applications. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Electron spin dynamics in excited state photochemistry: recent development in the study of intersystem crossing and charge transfer in organic compounds

Electron spin dynamics are crucial to photochemical and photophysical processes. However, to a large extent, they are neglected in routine photochemistry studies. Herein, we summarized the recent developments of electron spin dynamics in organic molecular systems. The electron-spin selective intersystem crossing (ISC) as well as charge separation (CS) and charge recombination (CR) of the organic molecular system are discussed, including ISC of the compounds with twisted π-conjugation frameworks and CR-induced ISC in compact orthogonal electron donor-acceptor dyads. We found that the electron spin polarization (ESP) of the triplet state formed in these systems is highly dependent on the molecular structure and geometry. The zero-field-splitting (ZFS) D and E parameters of the triplet state of series chromophores determined with time-resolved electron paramagnetic resonance (TREPR) spectroscopy are presented. Some unanswered questions in related areas are raised, which may inspire further theoretical investigations. The examples demonstrate that the study of electron spin dynamics is not only important in fundamental photochemistry to attain in-depth understanding of the ISC and the charge transfer processes, but is also useful for designing new efficient organic molecular materials for applications including photodynamic therapy, organic light-emitting diodes, and photon upconversion.

Pathway and Length Control of Supramolecular Polymers in Aqueous Media via a Hydrogen Bonding Lock

Programming the organization of π-conjugated systems into nanostructures of defined dimensions is a requirement for the preparation of functional materials. Herein, we have achieved high-precision control over the self-assembly pathways and fiber length of an amphiphilic BODIPY dye in aqueous media by exploiting a programmable hydrogen bonding lock. The presence of a (2-hydroxyethyl)amide group in the target BODIPY enables different types of intra- vs. intermolecular hydrogen bonding, leading to a competition between kinetically controlled discoidal H-type aggregates and thermodynamically controlled 1D J-type fibers in water. The high stability of the kinetic state, which is dominated by the hydrophobic effect, is reflected in the slow transformation to the thermodynamic product (several weeks at room temperature). However, this lag time can be suppressed by the addition of seeds from the thermodynamic species, enabling us to obtain supramolecular polymers of tuneable length in water for multiple cycles.

Modulating the Optical Properties of BODIPY Dyes by Noncovalent Dimerization within a Flexible Coordination Cage

Aggregation of organic molecules can drastically affect their physicochemical properties. For instance, the optical properties of BODIPY dyes are inherently related to the degree of aggregation and the mutual orientation of BODIPY units within these aggregates. Whereas the noncovalent aggregation of various BODIPY dyes has been studied in diverse media, the ill-defined nature of these aggregates has made it difficult to elucidate the structure-property relationships. Here, we studied the encapsulation of three structurally simple BODIPY derivatives within the hydrophobic cavity of a water-soluble, flexible PdII6L4 coordination cage. The cavity size allowed for the selective encapsulation of two dye molecules, irrespective of the substitution pattern on the BODIPY core. Working with a model, a pentamethyl-substituted derivative, we found that the mutual orientation of two BODIPY units in the cage's cavity was remarkably similar to that in the crystalline state of the free dye, allowing us to isolate and characterize the smallest possible noncovalent H-type BODIPY aggregate, namely, an H-dimer. Interestingly, a CF3-substituted BODIPY, known for forming J-type aggregates, was also encapsulated as an H-dimer. Taking advantage of the dynamic nature of encapsulation, we developed a system in which reversible switching between H- and J-aggregates can be induced for multiple cycles simply by addition and subsequent destruction of the cage. We expect that the ability to rapidly and reversibly manipulate the optical properties of supramolecular inclusion complexes in aqueous media will open up avenues for developing detection systems that operate within biological environments.

How Water in Aliphatic Solvents Directs the Interference of Chemical Reactivity in a Supramolecular System

Water is typically considered to be insoluble in alkanes. Recently, however, monomerically dissolved water in alkanes has been shown to dramatically impact the structure of hydrogen-bonded supramolecular polymers. Here, we report that water in methylcyclohexane (MCH) also determines the outcome of combining a Michael reaction with a porphyrin-based supramolecular system. In dry conditions, the components of the reaction do not affect or destabilize the supramolecular polymer, whereas in ambient or wet conditions the polymers are rapidly destabilized. Although spectroscopic investigations show no effect of water on the molecular structure of the supramolecular polymer, light scattering and atomic force microscopy experiments show that water increases the flexibility of the supramolecular polymer and decreases the polymer length. Through a series of titrations, we show that a cooperative interaction, involving the coordination of the amine catalyst to the porphyrin and complexation of the substrates to the flexible polymers invokes the depolymerization of the aggregates. Water crucially stabilizes these cooperative interactions to cause complete depolymerization in humid conditions. Additionally, we show that the humidity-controlled interference in the polymer stability occurs with various substrates, indicating that water may play a ubiquitous role in supramolecular polymerizations in oils. By controlling the amount of water, the influence of a covalent chemical process on noncovalent aggregates can be mediated, which holds great potential to forge a connection between chemical reactivity and supramolecular material structure. Moreover, our findings highlight that understanding cooperative interactions in multicomponent noncovalent systems is crucial to design complex molecular systems.

Impact of Positional Isomerism on Pathway Complexity in Aqueous Media

Pathway complexity has become an important topic in recent years due to its relevance in the optimization of molecular assembly processes, which typically require precise sample preparation protocols. Alternatively, competing aggregation pathways can be controlled by molecular design, which primarily rely on geometrical changes of the building blocks. However, understanding how to control pathway complexity by molecular design remains elusive and new approaches are needed. Herein, we exploit positional isomerism as a new molecular design strategy for pathway control in aqueous self-assembly. We compare the self-assembly of two carboxyl-functionalized amphiphilic BODIPY dyes that solely differ in the relative position of functional groups. Placement of the carboxyl group at the 2-position enables efficient pairwise H-bonding interactions into a single thermodynamic species, whereas meso-substitution induces pathway complexity due to competing hydrophobic and hydrogen bonding interactions. Our results show the importance of positional engineering for pathway control in aqueous self-assembly.

Thermodynamic insights into the entropically driven self-assembly of amphiphilic dyes in water

Self-assembly of amphiphilic dyes and π-systems are more difficult to understand and to control in water compared to organic solvents due to the hydrophobic effect. Herein, we elucidate in detail the self-assembly of a series of archetype bolaamphiphiles bearing a naphthalene bisimide (NBI) π-core with appended oligoethylene glycol (OEG) dendrons of different size. By utilizing temperature-dependent UV-vis spectroscopy and isothermal titration calorimetry (ITC), we have dissected the enthalpic and entropic parameters pertaining to the molecules' self-assembly. All investigated compounds show an enthalpically disfavored aggregation process leading to aggregate growth and eventually precipitation at elevated temperature, which is attributed to the dehydration of oligoethylene glycol units and their concomitant conformational changes. Back-folded conformation of the side chains plays a major role, as revealed by molecular dynamics (MD) and two dimensional NMR (2D NMR) studies, in directing the association. The sterical effect imparted by the jacketing of monomers and dimers also changes the aggregation mechanism from isodesmic to weakly anti-cooperative.

Unprecedented green-emissive boranyl-hydrazone supramolecular assemblies and their in vitro diagnostic applications

This paper describes a novel symmetric N,N'-diethylsalicylaldehyde boranyl hydrazone (1) and its in situ-generated assemblies displaying opto-analytical capabilities for the diagnosis of nucleic acids under physiological conditions. The sensing capabilities of these unprecedented supramolecular assemblies were characterized using UV-Vis spectroscopy, fluorescence spectroscopy, 1D and 2D NMR spectroscopy, dynamic light scattering, and zeta potential measurements. Model compounds lacking boranyl units (2, 3) were prepared to correlate and evaluate the sensing mechanism. The rationally designed probe 1 displays unusual aggregation-induced emissive (AIE) properties, with an average particle size of 1096 nm exhibiting green emission upon excitation at 377 nm in pH-7.2 TRIZMA buffer. A selective switch on response toward organic PO₄^3- accompanied through specific nano-aggregations patterns and sizes, thereby causing a significant red-shift through AIE. Exploiting such switch on in green channel behavior has allowed the monitoring of DNase I activities and polymerase chain reactions.

pH Driven self-assembly of aza-BODIPY J-aggregates

A pH-driven self-assembly of a simple aza-BODIPY was discovered in PBS solution, whereby ion-specific J-aggregated nanostructures were generated at very low dye concentration (2.5–20 [Formula: see text]M). The aggregation process was investigated in different conditions (pH, temperature and time) by monitoring absorption spectral shifts and associated nanostructure morphological changes. The pH-driven self-assembly process demonstrated an instantaneous thermodynamic phenomenon associated with three characteristic structures, each with distinctive optical properties. When the sample was first formulated within a short time window, a thermodynamically less stable intermediate with an unusual morphology of triangular nanoplates and broad absorption was observed. The formation of these structures was independent of the ions in PBS solution (Na[Formula: see text], K[Formula: see text], thus indicating that the triangular structure was inherent to the anisotropic structure of aza-BODIPY scaffolds. The second structure associated with a metastable pathway generated a uniform population of spherical nanovesicles, while the third structure, generated through a more thermodynamically stable pathway consisted of fibers. The absorption spectra suggested that both spherical and fiber structures contributed to the J-aggregation band at 735 nm in the near infrared optical spectrum and their population in each formulation was concentration dependent. The results highlighted the significance of ion effects in self-assembly of aza-BODIPY and the mechanistic structural changes of the morphology. Furthermore, this fundamental discovery offers a versatile method for the self-assembly of aza-BODIPY J-aggregates as a new nanoplatform with potential photonic applications.

Supramolecular polymerization: challenges and advantages of various methods in assessing the aggregation mechanism

Oligothiophenes with branched alkyl end groups show distinct aggregation in organic solvents. The process of supramolecular polymerization is assessed by three different methods (UV-vis absorption and fluorescence emission spectroscopy and dynamic light scattering) to exclude artifacts. An apparent dependence of the degree of aggregation on the concentration of the oligomers is observed. Above the upper limit of concentration (a lower micromolar range for the present class of compounds), experimental data delivered conflicting results and the concentration should not therefore be exceeded. Scanning force microscopy and molecular dynamics simulations confirm the formation of one-dimensional aggregates with presumably helical arrangement of the achiral monomers.

Null Exciton Splitting in Chromophoric Greek Cross (+) Aggregate

Exciton interactions in molecular aggregates play a crucial role in tailoring the optical behaviour of π-conjugated materials. Though vital for optoelectronic applications, ideal Greek cross-dipole (α=90°) stacking of chromophores remains elusive. We report a novel Greek cross (+) assembly of 1,7-dibromoperylene-3,4,9,10-tetracarboxylic tetrabutylester (PTE-Br₂ ) which exhibits null exciton coupling mediated monomer-like optical characteristics in the crystalline state. In contrast, nonzero exciton coupling in X-type (α=70.2°, PTE-Br₀ ) and J-type (α=0°, θ=48.4°, PTE-Br₄ ) assemblies have perturbed optical properties. Additionally, the semi-classical Marcus theory of charge-transfer rates predicts a selective hole transport phenomenon in the orthogonally stacked PTE-Br₂ . Precise rotation angle dependent optoelectronic properties in crystalline PTE-Br₂ can have consequences in the rational design of novel π-conjugated materials for photonic and molecular electronic applications.

Visible to NIR Light Photoactivation of Hydrogen Sulfide for Biological Targeting

The synthesis and photochemical properties of H₂S-releasing BODIPY thiocarbamate photocage scaffolds activatable by visible-to-NIR (up to 700 nm) light to release carbonyl sulfide (COS), which is transformed to H₂S using either isolated or natural carbonic anhydrase, is reported. The excellent uncaging cross section and high H₂S release yields in in vitro experiments, including live-cell imaging, suggest that these photocages can serve as a platform for the bio-orthogonal phototriggered release within the tissue-transparent window.

From isodesmic to highly cooperative: reverting the supramolecular polymerization mechanism in water by fine monomer design

Two structurally-similar discotic molecules able to self-assemble in water, forming supramolecular fibers, are reported. While both self-assembled polymers are indistinguishable from a morphological point-of-view, a dramatic change in their polymerization mechanism is observed (i.e., one self-assemble via an isodesmic mechanism, while the other shows one of the highest cooperativity values).

Solvent switchable nanostructures and the function of a π-amphiphile

This manuscript reports solvent tunable functional nano-assemblies of an unsymmetrical bola-shaped π-amphiphile (NDI-PY) which consists of a hydrophobic naphthalene-diimide (NDI) chromophore connected to a non-ionic hydrophilic wedge and a pyridine group at its two opposite arms. Importantly, it contains a hydrazide group located at the hydrophobic domain between the NDI-chromophore and the hydrophilic-wedge to drive the supramolecular assembly by directional H-bonding. NDI-PY exhibits spontaneous assembly in water as well as in a highly non-polar solvent like tetra-chloroethylene (TCE) by the synergistic effect of H-bonding and π-stacking interaction. Spectroscopy studies reveal almost identical self-assembly features in water and TCE with critical aggregation concentrations in the range of 0.3 mM, which matches the values obtained from the isothermal calorimetry (ITC) dilution experiment. Differential scanning calorimetry (DSC) experiments reveal a single endothermic peak at 31 °C (ΔH = -12.3 kJ mol^-1) and 40 °C (ΔH = -5.35 kJ mol^-1) for water and TCE, respectively, indicating marginally higher thermal stability in TCE, which is consistent with the FT-IR data, suggesting stronger H-bonding in TCE. Although the molecular assembly features appear to be similar, NDI-PY produces distinctly different mesoscopic structures in water and TCE. In water, it forms vesicles (D_h = 150-180 nm) with the pyridine groups displayed at the outer surface, while in TCE it generates a transparent gel (CGC = 8.0 mM) with a nanotubular (width ∼50 nm, wall thickness ∼10 nm) morphology. Powder X-ray diffraction studies show clearly different packing structures; in water a single sharp peak at the low angle (d = 19.3 Å, a little shorter than the extended length of the molecule) suggests the formation of a monolayer membrane, while in TCE several sharp peaks appear with the d values maintaining a ratio of 1 : 1/√3 : 1/2 : 1/√7 : 1/3 : 1/√12, indicating the formation of a 2D hexagonal lattice. Photoconductivity measurements reveal moderate electronic conduction in both cases. However, it shows a remarkable enhancement of the life time of the charge-carriers for the nanotubular structure compared to the vesicular morphology. On the other hand, the vesicles in water display antimicrobial activity against Gram-positive S. aureus with a highly promising MIC_LB value of 29.4 μg mL^-1. In contrast, it does not lyse human red blood cells even at as high a concentration as 2.5 mg mL^-1 (HC₅₀ > 2.5 mg mL^-1), implying high selectivity of the NDI-PY vesicles towards bacterial cells over mammalian cells. Display of the pyridine groups at the outer surface of the membrane enables molecular recognition by complementary H-bonding with a carboxylic acid group and thereby facilitates uptake of the attached pyrene chromophores in the NDI-membrane by charge-transfer interaction between the NDI acceptor and the pyrene donor. In fact a Job's plot experiment reveals maximum uptake at a 1 : 1 ratio of the NDI-PY and the pyrene guest, indicating all the pyridine groups are accessible at the vesicular surface.

Stimuli-Responsive Directional Vesicular Assembly with Tunable Surface Functionality and Impact on Enzyme Inhibition

The article describes the self-assembly of a series of unsymmetrical bola-shaped π-amphiphiles (NDI-1, NDI-1a, NDI-2, NDI-3, and NDI-4) consisting of a hydrophobic naphthalene-diimide (NDI) chromophore attached to a nonionic hydrophilic wedge and an anionic headgroup in the two opposite arms of the central NDI. By design, only a single hydrazide group is linked either on the ionic or nonionic arm of the NDI. NDI-1 and NDI-1a are regioisomers differing only in the location of the hydrazide group, placed in the nonionic or ionic arm, respectively. NDI-2, NDI-3, and NDI-4 are similar to NDI-1 in the placement of the hydrazide group but differ in the nature of the ionic headgroups. Except for NDI-2, all of them exhibit spontaneous vesicle structures in water (pH 9.0) as established by electron microscopy, small-angle neutron scattering, dynamic light scattering, and spectroscopy studies. Supramolecularly assembled oligo-oxyethylene chains of the hydrophobic wedge exhibited a lower critical solution temperature (LCST) at ∼40 °C, similar to that of covalent polymers. Consequently, above the LCST, the bola-amphiphile was converted to a single headgroup surfactant, resulting in the collapse of the vesicular structure to nanoparticles. In all examples, the dominant H-bonding force among the hydrazide groups resulted in unidirectional orientation, leading to the formation of a nonsymmetric membrane with the H-bonded chain located at the inner wall. Therefore, the functional group displayed in these vesicles could be fully dictated by the location of the hydrazide group. Thus, for NDI-1, NDI-3, or NDI-4, the hydrazide group, located at the nonionic arm, directed the nonionic wedge to converge at the inner wall of the vesicle by displaying the anionic headgroups toward the outer surface. In contrast, NDI-1a formed a nonionic vesicle because in this case anionic headgroups were located at the inner wall of the membrane. Furthermore, among NDI-1, NDI-3, and NDI-4, the charge density of the anionic surface and accordingly the radius of curvature and particle size could be tuned precisely as a function of the extent of charge delocalization in the phenoxide or carboxylate headgroup. These distinct self-assembly modes resulted in very different abilities of these vesicles for electrostatic-interaction-driven biomolecular recognition, which was studied by testing their ability to bind with cationic protein chymotripsin and inhibit its enzymatic activity. The enzyme inhibition ability followed the order NDI-1 > NDI-3 > NDI-4 > NDI-2 ≈ NDI-1a, which could be rationalized by their distinct functional group display and surface charge density factors.

An unprecedented amplification of near-infrared emission in a Bodipy derived π-system by stress or gelation

A meso-substituted Bodipy derived π-gelator exhibits amplified near-infrared (NIR) emission upon shearing of its film from n-decane or drying of its gel from DMSO.

We report an unprecedented strategy to generate and amplify near-infrared (NIR) emission in an organic chromophore by mechanical stress or gelation pathways. A greenish-yellow emitting film of π-extended Bodipy-1, obtained from n-decane, became orange-red upon mechanical shearing, with a 15-fold enhancement in NIR emission at 738 nm. Alternatively, a DMSO gel of Bodipy-1 exhibited a 7-fold enhancement in NIR emission at 748 nm with a change in emission color from yellow to orange-red upon drying. The reason for the amplified NIR emission in both cases is established from the difference in chromophore packing, by single crystal analysis of a model compound (Bodipy-2), which also exhibited a near identical emission spectrum with red to NIR emission (742 nm). Comparison of the emission features and WAXS and FT-IR data of the sheared n-decane film and the DMSO xerogel with the single crystal data supports a head-to-tail slipped arrangement driven by the N–H···F–B bonding in the sheared or xerogel states, which facilitates strong exciton coupling and the resultant NIR emission.

Supramolecularly Engineered π-Amphiphile

This article describes self-assembly of supramolecularly engineered naphthalene-diimide (NDI)-derived amphiphiles NDI-1 and NDI-2. They have the same hydrophobic/hydrophilic balance but merely differ by a single functional group, amide or ester. They exhibit distinct self-assembly in water; NDI-1 forms hydrogel, which upon aging forms crystals, whereas NDI-2 forms micelles as revealed by in-depth structural analysis using cryo-TEM, dynamic light scattering, and small-angle X-ray scattering studies. These results suggest that the H-bonding among the amide groups fully regulates the self-assembly by overruling the packing parameters. Further, the present study elucidates sharp lower critical solution temperature exhibited by these π-amphiphiles, which has been extensively studied for many important applications of water-soluble polymers but hardly known in the literature of small-molecule surfactants. Control experiments with the same water-soluble hydrophilic wedge did not show such a property, confirming this to be a consequence of the supramolecular polymerization by extended amide-amide H-bonding and not inherent to the structure of the hydrophilic wedge containing oligo-oxyethylene chains.

Influence of Metal, Ligand and Solvent on Supramolecular Polymerizations with Transition-Metal Compounds: A Theoretical Study

The nature of intermolecular interactions governing supramolecular polymerizations is very important for controlling their cooperativity. In order to address this problem, supramolecular columns made of Pt^II and Pd^II complexes of oligo(phenylene ethynylene)-based pyridine (OPE) and tetrazolylpyridine ligands (TEP) were investigated through the dispersion-corrected PM6 method. Aromatic, CH-π, M-Cl and metallophilic interactions helped stabilize the supramolecules studied, and their geometries and associated cooperativities were in excellent agreement with experimental data. The OPE ligand and/or the presence of Pt^II led to stronger metallophilic interactions and also to cooperative supramolecular polymerizations, which clearly suggests that metallophilic interactions are a key factor for controlling cooperativity. The results indicate that sequential monomer addition is in general less spontaneous than the combination of two larger preformed stacks. The present theoretical investigations contribute to the further understanding of the relation between the thermodynamics of supramolecular polymerizations and the nature of different synthons.

Amphiphilic BODIPY derivatives: the solvophobic effect on their photophysical properties and bioimaging in living cells

Three novel amphiphilic BODIPY derivatives were prepared and their photophysical properties in THF/water mixtures with varying fractions of water were investigated. BDP-1 could self-assemble into different vesicle architectures in aqueous solution, while BDP-2 and BDP-3 with more hydrophilic abilities formed spherical and worm-like micelles. The BODIPY derivatives could be absorbed by HeLa cells and showed no apparent toxicity during the course of the test. In particular, unlike traditional amines or morpholinyl functionalized lysosome fluorescent probes, BDP-1 nanovesicles without targeted groups exhibit red emission and show effective lysosome biological imaging. Co-staining experiments with lysosome specific trackers further confirmed the disassembly of BDP-1 nanovesicles in lysosomes. This research provides a new avenue of using probes without targeting the structural unit to stain special organelles and shows potential applications in cell imaging fields.

The origin of emissive states of carbon nanoparticles derived from ensemble-averaged and single-molecular studies

At present, there is no consensus understanding on the origin of photoluminescence of carbon nanoparticles, particularly the so-called carbon dots. Providing comparative analysis of spectroscopic studies in solution and on a single-molecular level, we demonstrate that these particles behave collectively as fixed single dipoles and probably are the quantum emitter entities. Their spectral and lifetime heterogeneity in solutions is explained by variation of the local chemical environment within and around luminescence centers. Hence, the carbon dots possess a unique hybrid combination of fluorescence properties peculiar to dye molecules, their conjugates and semiconductor nanocrystals. It is proposed that their optical properties are due to generation of H-aggregate-type excitonic states with their coherence spreading over the whole nanoparticles.

Spectroscopic differentiation between monomeric and aggregated forms of BODIPY dyes: Effect of 1,1-dichloroethane

1,1-Dichloroethane (1,1-DCE) can induce spectroscopic differentiation between aggregated and monomeric forms of BODIPY dyes.

Self-assembly of alkynylplatinum(II) terpyridine amphiphiles into nanostructures via steric control and metal-metal interactions

A series of mono- and dinuclear alkynylplatinum(II) terpyridine complexes containing the hydrophilic oligo(para-phenylene ethynylene) with two 3,6,9-trioxadec-1-yloxy chains was designed and synthesized. The mononuclear alkynylplatinum(II) terpyridine complex was found to display a very strong tendency toward the formation of supramolecular structures. Interestingly, additional end-capping with another platinum(II) terpyridine moiety of various steric bulk at the terminal alkyne would lead to the formation of nanotubes or helical ribbons. These desirable nanostructures were found to be governed by the steric bulk on the platinum(II) terpyridine moieties, which modulates the directional metal-metal interactions and controls the formation of nanotubes or helical ribbons. Detailed analysis of temperature-dependent UV-visible absorption spectra of the nanostructured tubular aggregates also provided insights into the assembly mechanism and showed the role of metal-metal interactions in the cooperative supramolecular polymerization of the amphiphilic platinum(II) complexes.

Color-Tunable Cyano-Substituted Divinylene Arene Luminogens as Fluorescent π-Gelators

The synthesis of three cyano-substituted divinylene π-gelators is reported. The modulation of the color is achieved by placing the cyano groups in appropriate position of the conjugated backbone, thus modulating the donor-acceptor interaction. Variable-temperature UV-vis data have been utilized to investigate the self-assembly of the gelators 1-3 that is governed by a cooperative mechanism. A complete set of photophysical parameters (ΦF,τ, kr and knr) demonstrate the role of the molecular aggregation in enhanced emission upon self-assembly.

Strategies to create hierarchical self-assembled structures via cooperative non-covalent interactions

Cooperative phenomena are common processes involved in the hierarchical self-assembly of multiple systems in nature, such as the tobacco mosaic virus and a cell's cytoskeleton. Motivated by the high degree of order exhibited by these systems, a great deal of effort has been devoted in the past two decades to design hierarchical supramolecular polymers by combining different classes of cooperative interactions. In this review, we have classified the field of supramolecular polymers depending on the cooperative non-covalent forces driving their formation, with particular emphasis on recent examples from literature. We believe that this overview would help scientists in the field to design novel self-assembled systems with improved complexity and functionalities.

Metallogels self-assembled from linear rod-like platinum complexes: influence of the linkage

Two linear rod-like platinum complexes, which only differed in the linkage, were prepared. They both self-assemble into metallogels in nonpolar solvents; however, a very big contrast was observed. Unexpectedly, a much weaker gel was acquired upon replacing the ester linkage by an amide group. The intermolecular hydrogen bonding offered by the amide motif leads to a different stacking fashion and mechanism. The results demonstrated herein contribute to the rational design of metallogels as well as other functional supramolecular materials.