Designing Unconventional Molecular Ternary INHIBIT Logic Gate and Crafting Multifunctional Molecular Logic Systems

The paper describes an improved method for building flexible interswitchable logic gates such as rare-type molecular ternary INHIBIT and combinational logic circuits using a specially designed pyridine-end oligo-p-phenylenevinylene compound featuring alkyl substituents (-C16H33) in a THF medium. The probe molecule showed distinct opto-chemical signals upon interaction with Cu(II) and Hg(II) in THF medium. It is interesting to note that the presence of certain anions (S2-, I-, and CN-) could specifically mask the interaction of either of these metal ions or both. The most exciting thing is that we used a completely new gate design technique to construct a rare-type ternary INHIBIT logic gate using Cu(II), Hg(II), and CN- ions as three chemical inputs. With the identical set of chemical inputs, two more ternary combinational logic circuits were created out of these case-specific, independent reversible and irreversible spectroscopic studies. Finally, we were able to design adaptive molecular logic systems composed of several logic gates, including NOR, AND, IMPLICATION, INHIBIT, TRANSFER, and COMPLEMENT, that in this specific situation change the sort of logic sense by effortless optical toggling.

Aggregate-state-dependent photochromism and circularly polarized luminescence of a chiral biquinoline amphiphile

The photophysical and chiroptical properties of a chiral biquinoline amphiphile were found to be closely related to its aggregate states. Photochromism through photo-induced radical and circularly polarized luminescence were realized in its gel state and thin film state, respectively.

Ultraviolet light blocking optically clear adhesives for foldable displays via highly efficient visible-light curing

In developing an organic light-emitting diode (OLED) panel for a foldable smartphone (specifically, a color filter on encapsulation) aimed at reducing power consumption, the use of a new optically clear adhesive (OCA) that blocks UV light was crucial. However, the incorporation of a UV-blocking agent within the OCA presented a challenge, as it restricted the traditional UV-curing methods commonly used in the manufacturing process. Although a visible-light curing technique for producing UV-blocking OCA was proposed, its slow curing speed posed a barrier to commercialization. Our study introduces a highly efficient photo-initiating system (PIS) for the rapid production of UV-blocking OCAs utilizing visible light. We have carefully selected the photocatalyst (PC) to minimize electron and energy transfer to UV-blocking agents and have chosen co-initiators that allow for faster electron transfer and more rapid PC regeneration compared to previously established amine-based co-initiators. This advancement enabled a tenfold increase in the production speed of UV-blocking OCAs, while maintaining their essential protective, transparent, and flexible properties. When applied to OLED devices, this OCA demonstrated UV protection, suggesting its potential for broader application in the safeguarding of various smart devices.

Supramolecular alternating copolymers with highly efficient fluorescence resonance energy transfer

This article reports alternating supramolecular copolymerization of two naphthalene-diimide (NDI)-derived building blocks (NDI-1 and NDI-2) under thermodynamic control. Both monomers contain a central NDI chromophore, attached to a hydrocarbon-chain and a carboxylic-acid group. The NDI core in NDI-2 is symmetrically substituted with two butane-thiol groups, which makes it distinct from NDI-1. In decane, a 1 : 1 mixture of NDI-1 and NDI-2 shows spontaneous gelation and a typical fibrillar network, unlike the behavior of either of the components individually. The solvent-dependent UV/vis spectrum of the mixed sample in decane shows bathochromically shifted sharp absorption bands and a sharp emission band (holds a mirror-image relationship) with a significantly small Stokes shift compared to those in CHCl3, indicating J-aggregation. In contrast, the aggregated spectra of the individual monomers show broad structureless features, suggesting ill-defined aggregates. Cooling curves derived from the temperature-dependent UV/vis spectroscopy studies revealed early nucleation and a signature of well-defined cooperative polymerization for the mixed sample, unlike either of the individual components. Molecular dynamics simulations predicted the greatest dimer formation tendency for the NDI-1 + NDI-2 (1 : 1), followed by pure NDI-1 and NDI-2. Theoretical studies further revealed a partial positive charge in the NDI ring of NDI-1 when compared to NDI-2, promoting the alternating stacking propensity, which is also favored by the steric factor as NDI-2 is core-substituted with alkyl thiols. Such theoretical predictions fully corroborate with the experimental results showing 1 : 1 stoichiometry (from Job's plot) of the two monomers, indicating alternate stacking sequences in the H-bonded (syn-syn catemer type) supramolecular copolymer. Such alternating supramolecular copolymers showed highly efficient (>93%) fluorescence resonance energy transfer (FRET).

Self-Assembly of the Tetraphenylethylene-Capped Diserine through a Hierarchical Assembly Process

We report a new peptide-based urchin-shaped structure prepared through two-step self-assembly of tetraphenylethylene-diserine (TPE-SS). Hydrogelation generated nanobelts through the first stage of self-assembly of TPE-SS; these nanobelts further transformed on silicon wafers into urchin-like microstructures featuring nanosized spines. The presence of the TPE moiety in the hydrogelator resulted in aggregation-induced emission characteristics both in the solution and in the gel phases. TPE-SS has the lowest molecular weight of any TPE-capped hydrogelator with β-sheet-like structures under physiological pH. This new design strategy appears to be useful for generating three-dimensional self-assembled microstructures and multifunctional biomaterials. We found that TPE-SS is biocompatible with human mesenchymal stem cells and breast cancer cells, making them potential applications in tissue engineering and biomedical research.

Multistimuli-Responsive Chromism of Vinylene-Linked Bisflavin Based on the Aggregation and Redox Properties

Multistimuli-responsive chromism was observed for vinylene-linked bisflavin 1 a with an extended π-conjugated platform. The yellow emission of a dilute solution of 1 a in CHCl₃ (0.2 mM) observed at 298 K under UV excitation was changed to orange or red emission upon (1) an increase of concentration, (2) a decrease of temperature, and (3) variation of the solvent. This is in contrast to the almost non stimuli-responsive chromism of the N-methylated bisflavin analogue 1 b and monoflavin 2 a. Mechanistic investigation by ¹ H NMR analysis under various conditions revealed that the extended π-conjugation platform and imide moiety of 1 a generate controllability in the formation of lower- and higher-ordered aggregates, which induce variation of the emission color upon change. Bisflavin 1 a also exhibited redox-induced chromism, where the orange emission of 1 a was quenched by the addition of hydrazine under anaerobic conditions, and changed back to the original emission upon subsequent bubbling of O₂ gas.

Membrane-intercalating conjugated oligoelectrolytes

By acting as effective biomimetics of the lipid bilayers, membrane-intercalating conjugated oligoelectrolytes (MICOEs) can spontaneously insert themselves into both synthetic lipid bilayers and biological membranes. The modular and intentional molecular design of MICOEs enable a range of applications, such as bioproduction, biocatalysis, biosensing, and therapeutics. This tutorial review provides a structural evolution of MICOEs, which originated from the broader class of conjugated molecules, and analyses the drivers behind this evolutionary process. Various representative applications of MICOEs, accompanied by insights into their molecular design principles, will be reviewed separately. Perspectives on the current challenges and opportunities in research on MICOEs will be discussed at the end of the review to highlight their potential as unconventional and value-added materials for biological systems.

Recent Development in Sensitizers for Lanthanide-Doped Upconversion Luminescence

The attractive features of lanthanide-doped upconversion luminescence (UCL), such as high photostability, nonphotobleaching or photoblinking, and large anti-Stokes shift, have shown great potentials in life science, information technology, and energy materials. Therefore, UCL modulation is highly demanded toward expected emission wavelength, lifetime, and relative intensity in order to satisfy stringent requirements raised from a wide variety of areas. Unfortunately, the majority of efforts have been devoted to either simple codoping of multiple activators or variation of hosts, while very little attention has been paid to the critical role that sensitizers have been playing. In fact, different sensitizers possess different excitation wavelengths and different energy transfer pathways (to different activators), which will lead to different UCL features. Thus, rational design of sensitizers shall provide extra opportunities for UCL tuning, particularly from the excitation side. In this review, we specifically focus on advances in sensitizers, including the current status, working mechanisms, design principles, as well as future challenges and endeavor directions.

Polarity and strong sensitivity to external electric field in azacrown oligophenylenevinylene

Complex study of quadrupolar azacrown dye (E,E)-5,5́-Bis[2-(4-(4',7',10',13',16'-pentaoxa-1 azacyclooctadecyl)phenyl)ethenyl]-2,2́-bipyridine 1 was performed. Electronic spectra of absorption and fluorescence in different solvents exhibit strong solvatochromism. Electrooptical absorption measurements (EOAM) were performed to determine the electric dipole moments. These measurements gave large values of dipole moments in the ground μ_g and Franck-Condon excited state μ_e^FC equal to 6.8 ± 0.14C m and 39.3 ± 0.3C m, respectively. Furthermore, the results of EOAM suggest the existence two conformers in the ground state with close energies of electronic transitions. Density functional theory (DFT) calculations directly show that the shape of this molecule is not planar in the ground state and also allows the existence of two stable conformers with close energies. They appeared due to different orientations of the left and right pyridine fragments of the solute. The energies, electric dipole moments and dependences of dipole moments on the strength of applied electric field were calculated for found stable conformers of 1. DFT calculations with TD / B3LYP / 3-21G and cc-pVDZ (Time Depend) approach show that external electric field increases dramatically the dipole moments of the solute under study. The higher field intensity the larger the excited electric dipole in the range intensities from zero to ∼ 2.8·× 10 ⁹ V/m.

An Artificial Light-Harvesting System with Controllable Efficiency Enabled by an Annulene-Based Anisotropic Fluid

The development of controllable artificial light-harvesting systems based on liquid crystal (LC) materials, i.e., anisotropic fluids, remains a challenge. Herein, an annulene-based discotic LC compound 6 with a saddle-shaped cyclooctatetrathiophene core has been synthesized to construct a tunable light-harvesting platform. The LC material shows a typical aggregation-induced emission, which can act as a suitable light-harvesting donor. By loading Nile red (NiR) as an acceptor, an artificial light-harvesting system is achieved. Relying on the thermal-responsive self-assembling ability of 6 with variable molecular order, the efficiency of such 6-NiR system can be controlled by temperature. This light-harvesting system works sensitively at a high donor/acceptor ratio as 1000 : 1, and exhibits a high antenna effect (39.1) at a 100 : 1 donor/acceptor ratio. This thermochromic artificial light-harvesting LC system could find potential applications in smart devices employing soft materials.

Deciphering Internal and External π-Conjugation in C3 -Symmetric Multiple Azobenzene Connected Systems in Self-Assembly

Two tripodal C₃ -symmetric photoswitchable molecular systems T1 and T2 are reported that have extended conjugation at external and internal positions using an acryl group. The influence of the extended π-bonds in their absorption properties, thermal relaxation of the photoisomers and their propensities in forming supramolecular self-assemblies have been explored through spectroscopy, and microscopic studies. In particular, the investigations on the self-assembly have been carried out using scanning electron microscopy (SEM), transmission electron microscopy (TEM), polarized optical microscopy (POM), X-ray diffraction studies (XRD) and atomic force microscopy (AFM). Remarkably, the position of the acryl group influences the behaviour of the two target molecules in supramolecular assembly, and also in the formation of photoresponsive organic hydrogels or microcrystals.

Self-Assembly and Photochemistry of a Pyrene-Methyl Viologen Supramolecular Fiber System

This paper reports the self-assembly of a donor-acceptor system into nanoscopic structures and the photo processes taking place within these structures. The donor employed is pyrene linked to two β-cyclodextrin molecules (CD-PY-CD), and adamantane-linked methyl viologen attached to the three arms of mesitylene (Ms-(MV²⁺-AD)₃) is the acceptor. CD-PY-CD and Ms-(MV²⁺-AD)₃ when dissolved in water self-assembled into vesicles, which joined together to give long fibers. The self-assembly was studied using spectroscopic and microscopic techniques. Fluorescence of the pyrene chromophore was quenched within the self-assembled system due to efficient photoinduced electron transfer to methyl viologen. Photoinduced electron transfer within the assembly is confirmed through identification of product radical ions in flash photolysis experiments. Steady-state irradiation of the self-assembled system in an optical bench led to the formation of methyl viologen radical cation, which was stable for a few hours. Longevity of the radical cation was attributed to the fast reaction of pyrene radical cation with adjacent pyrene to give an unstable adduct, which slows down the back electron transfer process.

A stimuli-responsive pillar[5]arene-based hybrid material with enhanced tunable multicolor luminescence and ion-sensing ability

Tunable luminescent materials are becoming more and more important owing to their broad application potential in various fields. Here we construct a pillar[5]arene-based hybrid material with stimuli-responsive luminescent properties and ion-sensing abilities from a pyridine-modified conjugated pillar[5]arene and a planar chromophore oligo(phenylenevinylene) upon coordination of Cd (II) metal cores. This new material not only shows an optimized luminescence due to the minimized π-π stacking and efficient charge transfer properties benefitting from the existence of pillar[5]arene rings, but also exhibits tunable multicolor emission induced by different external stimuli including solvent, ions and acid, indicating great application potential as a fluorescent sensory material, especially for Fe3+. With this pillar[5]arene-based dual-ligand hybrid material, valid optimization and regulation on the fluorescence of the original chromophore have been achieved, which demonstrates a plausible strategy for the design of tunable solid-state luminescent materials and also a prototypical model for the effective regulation of fluorescent properties of planar π systems using synthetic macrocycle-based building blocks.

Understanding the role of conjugation length on the self-assembly behaviour of oligophenyleneethynylenes

Oligophenyleneethynylenes (OPEs) are prominent building blocks with exciting optical and supramolecular properties. However, their generally small spectroscopic changes upon aggregation make the analysis of their self-assembly challenging, especially in the absence of additional hydrogen bonds. Herein, by investigating a series of OPEs of increasing size, we have unravelled the role of the conjugation length on the self-assembly properties of OPEs.

Supramolecular and suprabiomolecular photochemistry: a perspective overview

In this perspective review article, we have attempted to bring out the important current trends of research in the areas of supramolecular and suprabiomolecular photochemistry. Since the spans of the subject areas are very vast, it is impossible to cover all the aspects within the limited space of this review article. Nevertheless, efforts have been made to assimilate the basic understanding of how supramolecular interactions can significantly change the photophysical and other related physiochemical properties of chromophoric dyes and drugs, which have enormous academic and practical implications. We have discussed with reference to relevant chemical systems where supramolecularly assisted modulations in the properties of chromophoric dyes and drugs can be used or have already been used in different areas like sensing, dye/drug stabilization, drug delivery, functional materials, and aqueous dye laser systems. In supramolecular assemblies, along with their conventional photophysical properties, the acid-base properties of prototropic dyes, as well as the excited state prototautomerization and related proton transfer behavior of proton donor/acceptor dye molecules, are also largely modulated due to supramolecular interactions, which are often reflected very explicitly through changes in their absorption and fluorescence characteristics, providing us many useful insights into these chemical systems and bringing out intriguing applications of such changes in different applied areas. Another interesting research area in supramolecular photochemistry is the excitation energy transfer from the donor to acceptor moieties in self-assembled systems which have immense importance in light harvesting applications, mimicking natural photosynthetic systems. In this review article, we have discussed varieties of these aspects, highlighting their academic and applied implications. We have tried to emphasize the progress made so far and thus to bring out future research perspectives in the subject areas concerned, which are anticipated to find many useful applications in areas like sensors, catalysis, electronic devices, pharmaceuticals, drug formulations, nanomedicine, light harvesting, and smart materials.

Energy transduction through FRET in self-assembled soft nanostructures based on surfactants/polymers: current scenario and prospects

The self-assembled systems of surfactants/polymers, which are capable of supporting energy funneling between fluorophores, have recently gained significant attraction. Surfactant and polymeric micelles form nanoscale structures spanning a radius of 2-10 nm are generally suitable for the transduction of energy among fluorophores. These systems have shown great potential in Förster resonance energy transfer (FRET) due to their unique characteristics of being aqueous based, tendency to remain self-assembled, spontaneous formation, tunable nature, and responsiveness to different external stimuli. This review presents current developments in the field of energy transfer, particularly the multi-step FRET processes in the self-assembled nanostructures of surfactants/polymers. The part one of this review presents a background and brief overview of soft systems and discusses certain aspects of the self-assemblies of surfactants/polymers and their co-solubilization property to bring fluorophores to close proximity to transduce energy. The second part of this review deals with single-step and multi-step FRET in the self-assemblies of surfactants/polymers and links FRET systems with advanced smart technologies including multicolor formation, data encryption, and artificial antenna systems. This review also discusses the diverse examples in the literature to present the emerging applications of FRET. Finally, the prospects regarding further improvement of FRET in self-assembled soft systems are outlined.

Supramolecular Ladder Assemblies as a Model for Probing Electronic Interactions between Multiple Stacked π-Conjugated Systems

A series of mono-, di-, and tri-topic receptors in which H-bonding sites, complementary to those of barbituric acid (BA), are fused is used to induce the supramolecular assembly of n×m ladders containing 1, 2, or 3 triphenylenevinylene units appended with BA. The topological constraint enforced by the architectures induces through-space interactions between the electroactive moieties that are reflected in the electronic absorption and emission spectrum. The n=2, m=2 or m=3 architectures undergo two single electron oxidation events, indicative of the formation of the corresponding mono- and di-radical cation species with comproportionation constants of 340 and 70, respectively. Comparison of the electrochemical potentials suggests that the charges are delocalized over the electroactive units in the assembly.

Ultrastrong Red Circularly Polarized Luminescence Promoted from Chiral Transfer and Intermolecular Förster Resonance Energy Transfer in Ternary Chiral Emissive Nematic Liquid Crystals

Chiral emissive liquid crystals (N*-LCs) have been proved to greatly amplify the circularly polarized luminescence (CPL) signals due to highly regular spiral arrangement of dyes in a well-organized liquid crystals system. Normally, CPL materials with a high luminescence dissymmetry factor (g_lum) and quantum yield (QY) can meet the real application requirement. Here, four chiral aggregate-induced emission (AIE) active donors (Guests A1-A4: R-C2, R-C4, R-C6, R-C8, chiral dopant, and energy donor) and achiral AIE-active acceptors (Guest B: PBCy, CPL emitter) were doped into the commercial nematic liquid crystals E7 (N-LCs, Host) to form CPL-active ternary chiral emissive N-LCs (T-N*-LCs), respectively. This kind of T-N*-LCs could emit strong red CPL with QY = 16.56% and g_lum up to 1.51 through intermolecular energy transfer and chirality induction from the supramolecular self-assembly of T-N*-LCs. This work provides the effective strategy for the development of high g_lum CPL materials.

Energy transfer designing in lanthanide-doped upconversion nanoparticles

Lanthanide (Ln3+)-doped upconversion nanoparticles (UCNPs), exhibiting excellent optical properties such as long photoluminescence lifetime, narrow emission bandwidth, and low autofluorescence background, have been applied in many fields, especially in biological analysis and medical diagnostics. Despite the exciting progress, the applications of Ln3+-doped UCNPs are hindered by the small absorption cross-section and low upconversion luminescence efficiency of Ln3+. To this regard, several effective strategies associated with energy transfer designing have been proposed to modulate the upconversion luminescence properties of Ln3+ in the past few decades. In this feature article, we focus on the most recent development of optical property designing in Ln3+-doped UCNPs on the basis of energy transfer between Ln3+-Ln3+, Ln3+-dyes, and Ln3+-quantum dots. Some future efforts towards the energy transfer designing in Ln3+-doped UCNPs are also proposed.

Electrostatically Driven Resonance Energy Transfer in an All-Quantum Dot Based Donor-Acceptor System

Demonstration of fundamental photophysical properties in environmentally friendly quantum dots (QDs) is essential to realize their practical use in various light harvesting applications. We accomplish here an efficient light induced resonance energy transfer in all-QD based donor-acceptor system in water, deprived of any commonly used organic dye component. Our nanohybrid system comprises surface engineered indium phosphide/zinc sulfide (InP/ZnS) QD as the donor, and copper indium sulfide/zinc sulfide (CIS/ZnS) QD as the acceptor. The electrostatic attraction between oppositely charged QDs is vital in achieving a strong ground state complexation in the [-] InP/ZnS:::[+] CIS/ZnS QD nanohybrid. A nonlinear Stern-Volmer plot confirms the involvement of both static and dynamic components in the PL quenching of InP/ZnS QD by CIS/ZnS QD. Moreover, a temporal evolution of resonance energy transfer is realized in the solid state as well, which can improve the potential of such "all-green QD" based nanohybrid systems for device level studies.

Self-Assembled Extended π-Systems for Sensing and Security Applications

Molecules and materials derived from self-assembled extended π-systems have strong and reversible optical properties, which can be modulated with external stimuli such as temperature, mechanical stress, ions, the polarity of the medium, and so on. In many cases, absorption and emission responses of self-assembled supramolecular π-systems are manifested several times higher when compared with the individual molecular building blocks. These properties of molecular assemblies encourage scientists to have a deeper understanding of their design to explore them for suitable optoelectronic applications. Therefore, it is important to bring in highly responsive optical features in π-systems, for which it is necessary to modify their structures by varying the conjugation length and by introducing donor-acceptor functional groups. Using noncovalent forces, π-systems can be put together to form assemblies of different shapes and sizes with varied optical band gaps through controlling intermolecular electronic interactions. In addition, using directional forces, it is possible to bring anisotropy to the self-assembled nanostructures, facilitating efficient exciton migration, resulting in the modulation of optical and electron-transport properties. In this Account, we mainly summarize our findings with optically tunable self-assemblies of extended π-systems such as p-phenylenevinylenes (PVs), p-phenyleneethynylenes (PEs), and diketopyrrolopyrroles (DPPs) as different stimuli-responsive platforms to develop sensors and security materials. We start with how PV self-assemblies and their coassemblies with appropriate electron-deficient systems can be used for the sensing of analytes in contact mode or in the vapor phase. For example, whereas the PV having electron-deficient terminal groups has high sensitivity toward trinitrotoluene (TNT) in contact mode, the supercoiled fibers formed by the coassembly of self-sorted stacks of C₃-symmetrical PV and C₃-symmetrical electron-deficient perylene bisimide are capable of sensing vapors of nitrobenzene and o-toluidine. The power of different functional groups in combination with PVs has been further illustrated by attaching CO₂-sensitive tertiary amine moieties to a cyano-substituted PV, which allowed the bimodal detection of CO₂ using fluorescence and Raman spectroscopy. Interestingly, the functionalization of PVs with terminal amide groups and chiral alkoxy side chains provided a mechanochromic system that allows self-erasable imaging. Whereas PVs exhibit quenching of fluorescence in most cases during self-assembly, PE derivatives exhibit aggregation-induced emission. This property of PEs has been exploited for the development of stimuli-responsive security materials, especially for currency and documents. For instance, the blue fluorescence of a PE attached to hydrophilic oxyethylene side chains coated on a filter paper upon contact with water changes to cyan emission due to the change in the molecular packing. Interestingly, the molecular packing of a Bodipy-attached PE-based gelator allowed a stress-induced change in the emission behavior, resulting in strong near-infrared (NIR) emission upon the application of mechanical stress or gelation. Finally, the use of DPP-based π-systems for the development of NIR transparent optical filters that block UV-vis light and their security- and forensic-related applications are described. These selected examples of the π-system self-assemblies provide an idea of the current status and future opportunities for scientists interested in this field of self-assembly and soft materials research.

Living Supramolecular Polymerization of an Aza-BODIPY Dye Controlled by a Hydrogen-Bond-Accepting Triazole Unit Introduced by Click Chemistry

An aza-BODIPY dye 1 bearing two hydrophobic fan-shaped tridodecyloxybenzamide pendants through 1,2,3-triazole linkages was synthesized by a click reaction and characterized. ¹ H NMR studies indicated that dye 1 exhibited variable conformations through intramolecular H-bonding interaction, which is beneficial for the polymorphism of aggregation. The thermodynamic, structural, and kinetic aspect of the supramolecular polymerization of dye 1 was investigated by UV/Vis absorption spectroscopy, IR spectroscopy, AFM, TEM, and SEM. Biphasic aggregation pathways of dye 1, leads to the formation of off-pathway, metastable Agg. I and thermodynamically stable Agg. II with distinct H-aggregation spectra and nanoscale morphology. The living manner of the supramolecular polymerization of dye 1 was demonstrated in seeded polymerization experiments with temperature-modulated successive cooling-heating cycles.

Self-Assembly of Diacetylene-Bridged Phenylenevinylene Oligomers in Water and Organic Solvents

Rodlike π-conjugated molecules in which two OPV fragments are connected through a diacetylene bond self-assemble in aqueous and organic media. Optical spectroscopy and AFM measurements indicated that, in water, strong hydrophobic interactions between π-cores promote aggregation into robust, uniform micellar structures. In contrast, in apolar solvents, a fibrilar morphology is obtained by coiling of columnar stacks. These stacks are formed in a nucleation-elongation process with degrees of cooperativity of 0.006, that is influenced by the low rotation barriers around the σ-bonds in the diacetylene linker.

Solvent-controlled assembly of pillar[5]arene-based supramolecular networks via π–π interactions for white light modulation

A supramolecular network based on pyrene-containing pillar[5]arene and a red emissive Eu(iii) complex was constructed, whose assembly and emission can be controlled by solvent polarity, eventually achieving white light emission.

Enhanced Energy Transfer in a Donor-Acceptor Photosensitizer Triggers Efficient Photodynamic Therapy

Photosensitizers (PSs) play a vital role in photodynamic therapy (PDT) for combating bacterial resistance and treating tumor. In this study, we report new donor-acceptor porphyrin PSs with a cationic conjugated oligomer (OPV) as a donor unit and porphyrin (TPP) as an acceptor unit by covalent linkage and achieved a fluorescence resonance energy transfer efficiency of 99% owing to their strong spectral overlap and short distance. The ¹O₂ yield of porphyrin derivatives is 121% (rose bengal as the standard reference) by virtue of OPVs' excellent light-harvesting ability and high fluorescence resonance energy transfer efficiency, greatly exceeding those of oligomer and porphyrin derivatives reported in the literature. Additionally, the cationic donors significantly improved the water solubility, decreased the aggregation of porphyrin, and promoted the adherence of the PSs to cell membranes through electrostatic interactions. As a result, the D-A porphyrin PSs exhibit dramatic PDT treatment efficiency. The half-inhibitory concentration is as low as 33 and 88 nM for methicillin-resistant Staphylococcus aureus and Escherichia coli, respectively. Therefore, this study provides a new strategy to construct PSs with high ¹O₂ yield and an excellent treatment effect at a low dose of PSs, which is promising for application in PDT used to treat cancer and microbial infections.

Influence of chirality on fluorescence and resonance energy transfer

Electronically excited molecules frequently exhibit two distinctive decay mechanisms that rapidly generate optical emission: one is direct fluorescence and the other is energy transfer to a neighboring component. In the latter, the process leading to the ensuing "indirect" fluorescence is known as FRET, or fluorescence resonance energy transfer. For chiral molecules, both fluorescence and FRET exhibit discriminatory behavior with respect to optical and material handedness. While chiral effects such as circular dichroism are well known, as too is chiral discrimination for FRET in isolation, this article presents a study on a stepwise mechanism that involves both. Chirally sensitive processes follow excitation through the absorption of circularly polarized light and are manifest in either direct or indirect fluorescence. Following recent studies setting down the symmetry principles, this analysis provides a rigorous, quantum outlook that complements and expands on these works. Circumventing expressions that contain complicated tensorial components, our results are amenable for determining representative numerical values for the relative importance of the various coupling processes. We discover that circular dichroism exerts a major influence on both fluorescence and FRET, and resolving the engagement of chirality in each component reveals the distinct roles of absorption and emission by, and between, donor and acceptor pairs. It emerges that chiral discrimination in the FRET stage is not, as might have been expected, the main arbiter in the stepwise mechanism. In the concluding discussion on various concepts, attention is focused on the validity of helicity transfer in FRET.

Coverage-Controlled Polymorphism of H-Bonded Networks on Au(111)

We report on the self-assembly of a conformational flexible organic compound on Au(111) using scanning tunneling microscopy and low-energy electron diffraction measurements. We observed different conformers of the compound upon adsorption on the reconstructed Au(111) surface. Increasing the molecular coverage enhanced the lateral pressure, that is, parallel to the surface, favoring a coverage-controlled transition from a supramolecular network displaying only one molecular organization, into a polymorphic array with two coexisting arrangements. Our results give insights into the role of substrate-induced conformational changes on the formation of polymorphic supramolecular networks.

Bimodal detection of carbon dioxide using fluorescent molecular aggregates

Fluorescent aggregates of a cyano-substituted phenylenevinylene derivative (R-1) have been used as a bimodal probe for the easy and fast detection of CO₂.

Fluorescence Resonance Energy Transfer (FRET): A Powerful Tool for Probing Amphiphilic Polymer Aggregates and Supramolecular Polymers

This Review Article highlights the utility of the fluorescence resonance energy transfer (FRET) to probe the dynamics and related issues in amphiphilic polymeric aggregates and supramolecular polymers. Amphiphilic polymers are more attractive compared to their small molecule analogues because they exhibit significantly lower critical aggregation concentration, relatively larger particle size (suitable for the enhanced permeation and retention effect), and a much slower dynamics of exchange between the unimer and the aggregate. Representative examples of exchange dynamics in amphiphilic polymer aggregates and their noncovalent encapsulation stability as a function of the structure of the macromolecule, cross-linking, environmental parameters, and biological conditions, as probed by FRET studies, have been included in this article. Further, related observations on the utility of FRET in studying the exchange dynamics in supramolecular polymers, particularly in aqueous medium, have been discussed at length, revealing a strong impact of chirality, side chain polarity, and other parameters. Overall, this Review Article brings out the strength of this technique to probe dynamics of aggregates and assembled systems, mostly in water medium, which has a paramount importance in designing future biomaterials.

H- and J-aggregates formed from a nontraditional π-gelator depending on the solvent polarity for the detection of amine vapors

A tert-butyl carbazole-modified difluoroboron β-diketonate complex (TCbzB) has been synthesized. Although no traditional gelation group was involved in TCbzB, it could form organogels in the mixed solvents of o-dichlorobenzene/cyclohexane (v/v = 1/5 or 1/2), toluene/cyclohexane (v/v = 1/2) and chlorobenzene/cyclohexane (v/v = 1/2). Interestingly, an orange organogel was obtained in o-dichlorobenzene/cyclohexane (v/v = 1/2) with relatively high polarity and red organogels were gained in the other three mixed solvents with relatively low polarity. TCbzB self-assembled into H-aggregates and J-aggregates in orange and red organogels, respectively, and the corresponding xerogels emitted yellow and red light, respectively, under UV illumination. The red emission of the xerogel-based film could be quenched significantly by gaseous n-propylamine and aniline because of the decomplexation of the difluoroboron β-diketonate complex by n-propylamine and the weak interactions between aniline and boron difluoride units.

Metal-Free All-Carbon Nanohybrid for Ultrasensitive Photoelectrochemical Immunosensing of alpha-Fetoprotein

C₆₀ can accept up to six electrons reversibly and show exceptional light absorption over the entire UV-vis spectrum, making it a potential photoactive probe for photoelectrochemical (PEC) bioassay. However, few successful works have been reported to apply fullerenes in PEC biosensing, partially because of the low electronic conductivity and poor interfacial interactions with targeted biomolecules. Herein, we report the addressing of these two obstacles by coupling high conductive graphite flake (Gr), graphene oxide (GO) with sufficient oxygen-containing functional groups, and an alkylated C₆₀ (AC₆₀) into a metal-free all-carbon nanohybrid (AC₆₀-Gr-GO) via harnessing delicate noncovalent interactions among them through a facile mechanical grinding. It was revealed that the as-obtained AC₆₀-Gr-GO nanohybrid not only showed conspicuous enhancement of photocurrent up to 35 times but also offered rich anchors for bioconjugation. With detection of alpha-fetoprotein as an example, the AC₆₀-Gr-GO based PEC immunosensor demonstrated a broad linear detection range (1 pg·mL^-1 to 100 ng·mL^-1) and a detection limit as low as 0.54 pg·mL^-1, superior/competitive to PEC immunosensors for AFP in previous reports. By a proper reinforcement in conductivity and biointerface engineering, this work may provide a new way to use fullerenes as photoactive materials in more general PEC biosensing.

Cooperative and FRET-Assisted Brightness Enhancement in Oligo(phenylene ethynylene): Quantum Dot Organic-Inorganic Nanohybrids

Herein, we combine the ideas of concerted emission from fluorophore ensembles and its further amplification through FRET in an organic-inorganic hybrid approach. Spherical and highly fluorescent organic nanoparticles (FONPs, Φ_f =0.38), prepared by the self-assembly of oligo(phenylene ethynylene) (OPE) molecules, were selected as a potential donor material. This organic core was then decorated with a shell of fluorescent CdSe/ZnS core-shell quantum dots (QDs; <d>≅5.5 nm, Φ_f =0.27) with the aid of a bifunctional ligand, mercaptopropionic acid. Its high extinction coefficient (ϵ≈4.1×10⁵  m^-1  cm^-1 ) and good spectral match with the emission of the FONPs (J(λ)≈4.08×10¹⁶  m^-1  cm^-1  nm⁴ ) made them a better acceptor candidate to constitute an efficient FRET pair (Φ_FRET =0.8). As a result, the QD fluorescence intensity was enhanced by more than twofold. The fundamental calculations carried out indicated an improvement in all the FRET parameters as the number of QDs around the FONPs was increased. This, together with the localization of multiple QDs in a nanometric dimension (volume≈1.8×10⁶  nm³ ), gave highly bright reddish luminescent hybrid particles as visualized under a fluorescence microscope.

Transforming a C 3-Symmetrical Liquid Crystal to a π-Gelator by Alkoxy Chain Variation

Rational understanding of the structural features involving different noncovalent interactions is necessary to design a liquid crystal (LC) or an organogelator. Herein, we report the effect of the number and positions of alkoxy chains on the self-assembly induced physical properties of a few π-conjugated molecules. For this purpose, we designed and synthesized three C ₃-symmetrical molecules based on oligo(p-phenylenevinylene), C ₃ OPV1-3. The self-assembly properties of these molecules are studied in the solid and solution states. All of the three molecules follow the isodesmic self-assembly pathway. Upon cooling from isotropic melt, C ₃ OPV1 having nine alkoxy chains (-OC₁₂H₂₅) formed a columnar phase with two-dimensional rectangular lattice and retained the LC phase even at room temperature. Interestingly, when one of the -OC₁₂H₂₅ groups from each of the end benzene rings is knocked out, the resultant molecule, C ₃ OPV2 lost the LC property, however, transformed as a gelator in toluene and n-decane. Surprisingly, when the -OC₁₂H₂₅ group from the middle position is removed, the resultant molecule C ₃ OPV3 failed to form either the LC or the gel phases.