Enantioselective Light Harvesting with Perylenediimide Guests on Self-Assembled Chiral Naphthalenediimide Nanofibers

Heparin binding induced supramolecular chirality into the self-assembly of perylenediimide bolaamphiphile

Chirality is one of the hallmarks of biomolecules. Herein, we utilize heparin, a chiral biomolecule and potent drug, to induce chiral organization into the assembly of an achiral molecule. Polyanionic heparin binds with a dicationic perylenediimide derivative to induce supramolecular helical organization in aqueous medium as well as in a highly competitive cell culture medium.

Discriminatory fluorescence and FRET in the chiral-perovskite/RhB system

Förster resonance energy transfer (FRET) holds a significant position in various natural and artificial systems, especially within donor-acceptor systems encompassing chiral components. Despite extensive investigations, a clear understanding of the effects of chirality and FRET on discriminatory fluorescence remains elusive. Here, chiral perovskite nanowires (CPNWs) and achiral rhodamine B (RhB) are employed to examine the FRET and discriminatory fluorescence behavior in a donor-acceptor system involving a chiral nanostructure. A notable FRET from the CPNWs to RhB is observed, along with circular dichroism (CD) and circularly polarized luminescence (CPL) activities in RhB. Although the FRET interaction remains consistent over time, a notable inversion in the polarity preference of the CD and CPL of RhB is observed. This reveals that the discriminatory fluorescence of the acceptor arises from the electromagnetic influence of the chiral donor. These findings elucidate that "chirality", as a property related to spatial orientation, cannot accompany the transfer of energy (which is a scalar) from chiral nanostructures to achiral molecules, which helps advance the understanding of the discriminatory fluorescence in the donor-acceptor system with a chiral nanostructure.

Circularly Polarized Phosphorescence of Benzils Achieved by Chiral Supramolecular Polymerization

In current approaches for circularly polarized phosphorescent materials, the crystallization of chiral phosphors suffers from poor processability, while integrating them into an amorphous polymer matrix results in unsatisfactory chiroptical signals due to the absence of chirality communication. Here, we have developed an innovative strategy through chiral supramolecular polymerization of benzil phosphors facilitated by intermolecular hydrogen bonds. The inherent film-forming capabilities of non-covalent supramolecular polymers obviate the need for an external polymer matrix. The pronounced helical asymmetry of benzil phosphors resulting from chiral supramolecular polymerization leads to enhanced circularly polarized phosphorescence compared to their non-hydrogen-bonded counterparts. The circularly polarized phosphorescent signals can be further modulated by varying the location of stereogenic centers or introducing halogen bonding to benzils. Incorporation of platinum(II) phosphor into the benzil supramolecular polymers induces both chirality and triplet-to-triplet energy transfer, leading to a change in circularly polarized phosphorescent color from yellow to red. In summary, chiral supramolecular polymerization of phosphors represents a novel and effective approach to circularly polarized phosphorescent materials.

Macroscopic handedness inversion of terbium coordination polymers achieved by doping homochiral ligand analogues

Inspired by natural biological systems, chiral or handedness inversion by altering external and internal conditions to influence intermolecular interactions is an attractive topic for regulating chiral self-assembled materials. For coordination polymers, the regulation of their helical handedness remains little reported compared to polymers and supramolecules. In this work, we choose the chiral ligands R-pempH2 (pempH2 = (1-phenylethylamino)methylphosphonic acid) and R-XpempH2 (X = F, Cl, Br) as the second ligand, which can introduce C-H⋯π and C-H⋯X interactions, doped into the reaction system of the Tb(R-cyampH)3·3H2O (cyampH2 = (1-cyclohexylethylamino)methylphosphonic acid) coordination polymer, which itself can form a right-handed superhelix by van der Waals forces, and a series of superhelices R-1H-x, R-2F-x, R-3Cl-x, and R-4Br-x with different doping ratios x were obtained, whose handedness is related to the second ligand and its doping ratio, indicating the decisive role of interchain interactions of different strengths in the helical handedness. This study could provide a new pathway for the design and self-assembly of chiral materials with controllable handedness and help the further understanding of the mechanism of self-assembly of coordination polymers forming macroscopic helical systems.

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.

Chiroptical Amplification of Induced Circularly Polarized Luminescence in Nucleotide-Templated Supramolecular Polymer

Efficient circularly polarized luminescence (CPL) from purely organic molecules holds great promise for applications in displays, sensing, and bioimaging. However, achieving high dissymmetry values (glum ) from organic chromophores remains a significant challenge. Herein, we present a bioinspired approach using adenosine triphosphate (ATP)-triggered supramolecular polymerization of a naphthalene diimide-derived monomer (ANSG) to induce CPL with a remarkable glum value of 1.1×10-2 . The ANSG molecules undergo a templated, chiral self-assembly through a cooperative growth mechanism in the presence of ATP, resulting in scrolled nanotubes with aggregation-induced enhanced emission (AIEE) and induced CPL. Furthermore, we demonstrate the concept of chiroptical amplification of induced CPL by efficiently amplifying asymmetry using a mixture of chiral ATP and achiral pyrophosphate. This innovative approach opens numerous opportunities in the emerging field of circularly polarized luminescence.

Stepwise Solution-Interfacial Nanoarchitectonics for Assembled Film with Full-Color and White-Light Circularly Polarized Luminescence

The fabrication of chiral thin films with tunable circularly polarized luminescence (CPL) colors is important in developing chiroptical materials but remains challenging due to the lack of assembly-initiated chiral film formation methodology. Here, by adopting a combined solution aggregation and interfacial assembly strategy, we report the fabrication of chiral film materials with full-color and white-light CPL. A biquinoline glutamic acid ester (abbreviated as BQGE) shows a typical aggregation-induced emission property with blue CPL after solution aggregation. Subsequent interfacial assembly of these solution aggregates on a solid substrate leads to the formation of a CPL active film consisting of nanobelt structures. Since the BQGE molecule has a coordination site, the CPL emission of an individual BQGE film can be extended from blue to green emission upon coordination with a zinc ion, accompanied by morphology transition from nanobelts to nanofibers. Further extension to red-color CPL is successfully achieved by coassembly with an achiral acceptor dye. Interestingly, the proper combination of coordination ratio and acceptor loading ratio provides bright white-light CPL emission from the BQGE/Zn²⁺/PDA triad composite film. This work provides a new approach to fabricating chiroptical film materials with controlled microscopic morphology and tunable CPL properties.

Oligothiophene-Ring-Strapped Perylene Bisimides: Functionalizable Coaxial Donor-Acceptor Macrocycles

Aesthetic designs from nature enable new knowledge to be gained and, at the same time, inspire scientific models. In this context, multicomponent macrocycles embody the advantage of precisely positioning the structural units to achieve efficient communication between them. However, the construction of a functionalizable macrocycle for ultrafast charge separation and stabilization has not been attempted. Herein, we report the synthesis, crystal structure, and transient absorption of a new functionalizable macrocycle consisting of an oligothiophene-ring-strapped perylene bisimide. Transient absorption results point to a sequential improvement in charge separation and stabilization from the macrocycle to the corresponding linear dimer and 2D polymer due to the unique design. Our macrocycle design with a supportive spatial arrangement of the donor and acceptor units will inspire the development of more complex synthetic systems with exciting electron-transfer and charge-separation features.

Construction of Artificial Light-Harvesting Systems Based on Aggregation-Induced Emission Type Supramolecular Self-Assembly Metallogels

A method for preparing new artificial light-harvesting systems (ALHSs) based on supramolecular metallogels was proposed. Various metal ions were introduced into a solution of a bi-benzimidazole compound (P) in ethylene glycol, and P exhibited high selectivity toward Al3+, as indicated by the noticeable red shift (49 nm) observed in the fluorescence spectra of P after the addition of Al3+. Interestingly, the gelator, P, could self-assemble into a stable supramolecular gel (P-gel) that exhibits strong aggregation-induced emission in ethylene glycol. Thus, two ALHSs were successfully prepared in a gel environment. The P-Al3+ assembly acts as the donor in the ALHSs, while BODIPY 505/515 (BDP) and rhodamine 6G (Rh6G), which are loaded onto the P-Al3+ assembly, act as acceptors. In these two diverse systems, the occurrence of an energy transfer process is confirmed from the P-Al3+ assembly to BDP and Rh6G. The findings of this study will enable the design and fabrication of ALHSs.

Chiral Naphthalenediimides with High-Efficiency Fluorescence and Circularly Polarized Luminescence in the Solid State for the Application in Organic Optoelectronics

Naphthalenediimides (NDIs) have been extensively studied due to their tunable luminescent properties. However, generally, the monomers or aggregates of non-core substituted NDIs exhibit low fluorescence quantum yields (Φ_FL <10 %) in the solid state, which limit their applications as light-emitting materials and render their chiral species unsuitable for circularly polarized luminescence (CPL). Herein, a series of non-core substituted chiral NDIs that exhibit high luminous efficiencies (Φ_FL up to 56.8 % for racemate and 36.5 % for enantiomer) and a strong CPL behavior in the solid state is reported. These significant improvements are attributed to the unique molecular conformation of the chiral NDIs and the formation of distinctive discrete dimers. The structures of the NDIs were significantly simpler and more accessible than those of other NDIs. The findings evidence that non-core substituted NDIs can exhibit strong fluorescence in the solid state and provide a new pathway to improve photophysical properties of NDIs.

Artificial light-harvesting systems based on supramolecular self-assembly multi-component metallogels

This paper proposes a strategy for fabricating new artificial light-harvesting systems (ALHSs) based on supramolecular multi-component metallogels. Al³⁺ was introduced into a solution of an acylhydrazone compound (L) in DMSO or DMF to form the L-Al³⁺ assembly. After adding Al³⁺ to the L solution, a noticeable blue shift appeared in the fluorescence spectra of L. Moreover, L could form a gel (L-B-gel) with 1,3:2,4-dibenzylidene sorbitol (B) in a DMSO-H₂O binary solution. Finally, we obtained a multi-component metallogel (L-Al³⁺-B-gel) and successfully fabricated two ALHSs (L-Al³⁺/rhodamine 6G (Rh6G) and L-Al³⁺/rhodamine B (RhB)). In these systems, the L-Al³⁺ supramolecular assembly acts as the donor, while Rh6G and RhB act as acceptors. Additionally, we confirmed an energy-transfer process from the L-Al³⁺ component to Rh6G and RhB separately. The proposed fabrication strategy will facilitate the development of ALHSs.

Reversible Chiral Optical Switching Based on Co-Assembled Spiropyran Gels

In recent years, it has been very interesting to dynamically adjust the emission of circularly polarized luminescence (CPL) materials through external stimulation due to their applications and the fundamental interest in them. In this work, luminescence-tunable and light-responsive supramolecular co-assembly CPL-active materials are fabricated by mixing an achiral functional spiropyran (SP-COOH) molecule with a chiral gelator. The spiropyran achieves a reversible change between a white closed ring state spiropyran and a purple zwitterionic merocyanine state in supramolecular co-assembly gels under alternate visible (vis) and ultraviolet (UV) light irradiation. The gel shows strong CPL signals due to the chirality transfer in co-assembly systems. These signals could change reversibly under alternate exposure to UV and vis light. Therefore, utilizing the multistimulus-responsive CPL signals in different states, a CPL switch of the supramolecular system signal according to the combinatorial control of UV-vis light irradiation is constructed.

Stereomutation and chiroptical bias in the kinetically controlled supramolecular polymerization of cyano-luminogens

The synthesis of two pairs of enantiomeric cyano-luminogens 1 and 2, in which the central chromophore is a p-phenylene or a 2,5-dithienylbenzene moiety, respectively, is described and their supramolecular polymerization under kinetic and thermodynamic control investigated. Compounds 1 and 2 form supramolecular polymers by quadruple H-bonding arrays between the amide groups and the π-stacking of the central aromatic moieties. In addition, the peripheral benzamide units are able to form intramolecularly H-bonded pseudocycles that behave as metastable monomer M* thus affording kinetically and thermodynamically controlled aggregated species AggI and AggII. The chiroptical and emissive features of compounds 1 and 2 strongly depend on the aggregation state and the nature of the central aromatic unit. Compounds 1 exhibit a bisignated dichroic response of different intensity but with similar sign for both AggI1 and AggII1 species, which suggests the formation of helical aggregates. In fact, these helical supramolecular polymers can be visualized by AFM imaging. Furthermore, both AggI and AggII species formed by the self-assembly of compounds 1 show CPL (circularly polarized light) activity of opposite sign depending on the aggregation state. Thienyl-derivatives 2 display dissimilar chiroptical, morphological and emissive characteristics for the corresponding kinetically and thermodynamically controlled aggregated species AggI and AggII in comparison to those registered for compounds 1. Thus, a stereomutation phenomenon is observed in the AggI2 → AggII2 conversion. In addition, AggI2 is arranged into nanoparticles that evolve to helical aggregates to afford AggII2. The dissimilar chiroptical and morphological features of AggI2 and AggII2 are also appreciated in the emissive properties. Thus, whilst AggI2 experiences a clear AIE (aggregation induced emission) process and CPL activity, the thermodynamically controlled AggII2 undergoes an ACQ (aggregation caused quenching) process in which the CPL activity is cancelled.

Fluorescence Resonance Energy Transfer Measurements in Polymer Science: A Review

Fluorescence resonance energy transfer (FRET) is a non-invasive characterization method for studying molecular structures and dynamics, providing high spatial resolution at nanometer scale. Over the past decades, FRET-based measurements are developed and widely implemented in synthetic polymer systems for understanding and detecting a variety of nanoscale phenomena, enabling significant advances in polymer science. In this review, the basic principles of fluorescence and FRET are briefly discussed. Several representative research areas are highlighted, where FRET spectroscopy and imaging can be employed to reveal polymer morphology and kinetics. These examples include understanding polymer micelle formation and stability, detecting guest molecule release from polymer host, characterizing supramolecular assembly, imaging composite interfaces, and determining polymer chain conformations and their diffusion kinetics. Finally, a perspective on the opportunities of FRET-based measurements is provided for further allowing their greater contributions in this exciting area.

Chirality-Controlled Supramolecular Donor-Acceptor Copolymerization with Distinct Energy Transfer Efficiency

Chirality delivers substantial value to the field of supramolecular polymers, not only serving as a probe to monitor the dynamic assembly process but providing access to chiroptical materials. The current study demonstrates that, for supramolecular donor-acceptor copolymers, their comonomer organization modes can be greatly influenced by stereocommunication at the molecular level. The enantiopure N-[(1R or 1S)-phenylethyl]benzamides are incorporated into two structurally similar comonomers, locating between the π-aromatic diethynylacene core and the alkyl chain peripheries. Parallel arrangement of the stereogenic methyl units brings steric hindrance between the homochiral comonomers, which is relieved for the heterochiral comonomers due to the adoption of staggered arrangement. It consequently steers randomly mixed organization for the homochiral supramolecular copolymers within the nanofibers. In comparison, the heterochiral counterparts form nanoparticles in an alternate donor-acceptor organization manner. The variation of comonomer arrangement modes gives rise to distinct energy transfer efficiency at the supramolecular level. Overall, the elaborate manipulation of stereogenic centers in the comonomer structures exerts significant impacts on the characteristics of supramolecular copolymers, which could be useful for chiral sensing, recognition, and optoelectronic applications.

Dynamic Control of a Multistate Chiral Supramolecular Polymer in Water

Natural systems transfer chiral information across multiple length scales through dynamic supramolecular interaction to accomplish various functions. Inspired by nature, many exquisite artificial supramolecular systems have been developed, in which controlling the supramolecular chirality holds the key to completing specific tasks. However, to achieve precise and non-invasive control and modulation of chirality in these systems remains challenging. As a non-invasive stimulus, light can be used to remotely control the chirality with high spatiotemporal precision. In contrast to common molecular switches, a synthetic molecular motor can act as a multistate chiroptical switch with unidirectional rotation, offering major potential to regulate more complex functions. Here, we present a light-driven molecular motor-based supramolecular polymer, in which the intrinsic chirality is transferred to the nanofibers, and the rotation of molecular motors governs the chirality and morphology of the supramolecular polymer. The resulting supramolecular polymer also exhibits light-controlled multistate aggregation-induced emission. These findings present a photochemically tunable multistate dynamic supramolecular system in water and pave the way for developing molecular motor-driven chiroptical materials.

Double helical π-aggregate nanoarchitectonics for amplified circularly polarized luminescence

The canonical double helical π-stacked array of base pairs within DNA interior has inspired the interest in supramolecular double helical architectures with advanced electronic, magnetic and optical functions. Here, we report a selective-recognized and chirality-matched co-assembly strategy for the fabrication of fluorescent π-amino acids into double helical π-aggregates, which show exceptional strong circularly polarized luminescence (CPL). The single crystal structure of the optimal combination of co-assemblies shows that the double-stranded helical organization of these π-amino acids is cooperatively assisted by both CH-π and hydrogen-bond arrays with chirality match. The well-defined spatial arrangement of the π-chromophores could effectively suppress the non-radiative decay pathways and facilitate chiral exciton couplings, leading to superior CPL with a strong figure of merit (glum = 0.14 and QY = 0.76). Our findings might open a new door for developing DNA-inspired chiroptical materials with prominent properties by enantioselective co-assembly initiated double helical π-aggregation.

Regulating the Excited State Chirality to Fabricate High-Performance-Solid-State Circularly Polarized Luminescence Materials

Developing solid-state materials and greatly improving the luminescence dissymmetry factors (g_lum) are the key issues for the future oriented practical application in the field of circularly polarized luminescence (CPL). However, most of the solid-state CPL-active materials suffer from aggregation caused emission quenching and relatively small g_lum values, which intensively restrict the development and application. In this work, high-performance CPL-active solid-state materials were achieved by regulating the excited state chirality of a series of bi-pyrene based chiral emitters. Due to the reversible mechanochromic luminescence under external stimuli, their excited state chirality can also be switched. It was found that the pristine amorphous powder possessed weak but obvious chiroptical properties because of the inherently chiral structures. Mechanical grinding could switch the fluorescence color and eliminate the CPL activity. Subsequently, by carrying out solvent fumigation, instant crystallization with well-defined microcrystal formation occurred, which could activate the CPL emission. Due to the chiral supramolecular arrangement of chromophores in the crystalline state, the resulting excimer emission in microcrystals showed chirality amplification not only in the excited state but also in the ground state. These findings not only provide a new method to fabricate high-performance CPL-active solid-state materials, but also clarify the chirality origin of pyrene-excimer-based chiral luminophores in various states which showed the importance of CPL as a probe of excited state chirality.

In situ instant crystallization significantly boosts the CPL performance in which both large circular polarization and high luminescence efficiency are achieved due to the chiral supramolecular arrangement of chromophores in the crystalline state.

Self-assembled lanthanide-based helixes: synthetic control of the helical handedness by chirality of the ligand

The control of the self-assembly of lanthanide helical chain and their helical handedness have been investigated for the first time. Δ- and Λ-form lanthanide chain complexes were obtained by introducing thiazolidine ligands that were synthesised from L- and D-cysteine, respectively, and shared the same formula: [Ln₂(L)₃(H₂O)₅]_∞·3H₂O (Ln: Sm and Eu) (L: 2-(2-hydroxy-3,5-dinitrophenyl)thiazolidine-4-carboxylic acid). The crystallographic, circular dichroism, and luminescence properties of these novel lanthanide chain complexes were studied.

Transpositional Circularly Polarized Luminescence from Transient Charge-Transfer Coassembly

Charge-transfer (CT) complexation between electron-rich and deficient aromatics has been widely applied in functional optical and photovoltaic materials. The selective complexation and spontaneous disassociation behavior of a dynamic charge-transfer coassembly possess potential in designing smart and dynamic luminescent materials, which however have not been addressed so far. In this work, the transient charge-transfer driven coassembly between π-conjugated amino acids and tetracyanobenzene, showing dynamic luminescent transition and circularly polarized luminescence (CPL) evolution property, is illustrated. Transient coassembly behaviors are independent to the diverse binding sites covering fluorene, naphthalene, and anthracene, attributed to the intramolecular CH…π interaction. Incorporation of fluorescent dyes enables a transient light harvesting process with hyperchromic CPL properties. Spontaneous green-to-red CPL transition hydrogels are also fabricated by embedding a competitive CT donor. Using a polymeric matrix treated by organic solvents, charge-transfer coassembly is immobilized with diverse circularly polarized luminescence. Such sensitive complexation shows applications in moisture-responsive luminescent materials and multiple luminescent color evolutions are realized.

Steering Triplet-Triplet Annihilation Upconversion through Enantioselective Self-Assembly in a Supramolecular Gel

Research on chiral selection and recognition not only is of fundamental importance in resolving the origin of biological homochirality, but also is instructive in the fabrication of controlled molecular organization in supramolecular systems to modulate their chirality-related functional properties. Here we report an enantioselective assembly process between a chiral energy donor and two enantiomeric energy acceptors, which further results in chirality-controlled energy transfer and enantioselective triplet-triplet annihilation upconversion (TTA-UC). It is found that the chiral energy donor Pd(II) octaethylporphyrin derivative PdOEP-LG12 (R_D) can selectively coassemble with the chiral energy acceptor LGAn (R_A) with the same chiral scaffold but tends to form segregation with the energy acceptor DGAn (S_A) with the opposite chiral scaffold in a thermodynamic equilibrium state. Thus, the coassembly of R_A/R_D shows more effective triplet-triplet energy transfer (TTET) and stronger upconverted luminescence and upconverted circularly polarized luminescence in comparison to the segregation of S_A/R_D. The establishment of such an enantioselective TTA-UC system highlights the applications of chirality-regulated triplet fusion in optoelectronic materials.

Self-Assembly and Circularly Polarized Luminescence from Achiral Pyrene-Adamantane Conjugates by Selective Inclusion with Cyclodextrins

The interaction between guest chromophores or lumiphores with host chiral cavity and their induced chirality is an important topic in supramolecular chemistry. Kodaka and Harata proposed a rule to explain the induced circular dichroism of the guest chromophores by host cyclodextrins. However, it remains unknown how a circularly polarized luminescence (CPL) signal will change when the lumiphores interacted with cyclodextrins in different modes. Here, we designed an achiral pyrene-adamantane conjugated guest molecule, N-(pyren-1-yl)adamantane-1-carboxamide (ACNP), and investigated its interactions with α/β/γ-cyclodextrins (CDs) and its induced CPL. Depending on the size match of the pyrene, adamantine with different cyclodextrins, distinct performance was observed. While α-CD could not induce a CPL signal of ACNP, β-CD could induce CPL in two modes, through adamantyl or direct pyrenyl induction, which could produce a CPL signal with opposite signs. γ-CD could always induce a negative CPL signal. Therefore, a rule of induced CPL of lumiphores by cyclodextrins can be proposed.

Fluorescein-bridged Perylene Bisimide Dimer for Use as Liquid Crystal: Studies on Mesomorphic and Fluorescence Properties

A novel fluorescein-bridged perylene bisimide (PBI) dimer for liquid crystal (LC) with geometrically symmetric structure was developed. The mesomorphic results indicated that the energetically stable and unstable conformers of fluorescein fragments could lead to the transformation of mesophases from a hexagonal columnar mesophase to an uncertain phase at 136.9 °C in heating, whilst a stable hexagonal columnar mesophase maintained between 175.6 °C and 58.6 °C in cooling. The selectively excited fluorescence characters in THF solution demonstrated that the fluorescence resonance energy transfer (FRET) effect between fluorescein fragments and PBI unites could provide a means to effectively impose strong fluorescence of the dimeric PBIs modified with suitable chromophore at the N-imide position, which alternatively serves as a platform for the further study of multi-functional PBI-based LCs.

Stereoselective Primary and Secondary Nucleation Events in Multicomponent Seeded Supramolecular Polymerization

Bioinspired, kinetically controlled seeded growth has been recently shown to provide length, dispersity, and sequence control on the primary structure of dynamic supramolecular polymers. However, command over the molecular organization at all hierarchical levels for the modulation of higher order structures of supramolecular polymers remains a formidable task. In this context, a surface-catalyzed secondary nucleation process, which plays an important role in the autocatalytic generation of amyloid fibrils and also during the chiral crystallization of small monomers, offers exciting possibilities for topology control in synthetic macromolecular systems by introducing secondary growth pathways compared to the usual primary nucleation-elongation process. However, mechanistic insights into the molecular determinants and driving forces for the secondary nucleation event in synthetic systems are not yet realized. Herein, we attempt to fill this dearth by showing an unprecedented molecular chirality control on the primary and secondary nucleation events in seed-induced supramolecular polymerization. Comprehensive kinetic experiments using in situ spectroscopic probing of the temporal changes of the monomer organization during the growth process provide a unique study to characterize the primary and secondary nucleation events in a supramolecular polymerization process. Kinetic analyses along with various microscopic studies further reveal the remarkable effect of stereoselective nucleation and seeding events on the (micro)structural aspects of the resulting multicomponent supramolecular polymers.

A new strategy for constructing artificial light-harvesting systems: supramolecular self-assembly gels with AIE properties

An artificial light-harvesting system (ALHS) has been designed and constructed based on supramolecular organogels made of a simple hydrazide-functionalized benzimidazole derivative (HB), as well as the fluorescent dye rhodamine B (RhB). RhB acted as a good acceptor to realize the energy-transfer process with good efficiency based on a HB/RhB assembly, which showed considerable fluorescence resonance energy transfer (FRET) efficiency of 53% for the energy transfer process. Remarkably, the obtained system showed superior color conversion abilities, converting blue light into orange light. By properly tuning the donor to acceptor ratio, bright orange light emission was achieved with a high fluorescence quantum yield of 35.5%. This system exhibited promise for applications relating to visible-light photo-transformation.

Switchable Circularly Polarized Luminescence in Supramolecular Gels through Photomodulated FRET

While the tremendous deal of efforts has been dedicated to the design and fabrication of materials with circularly polarized luminescence (CPL), the development of the chiroptical switch between different CPL signals is one of the important routes toward its application. Here, we prepared a supramolecular gel from the coassemblies containing a chiral gelator (9-fluoren-methoxycarbonyl-functionalized glutamate derivatives, FLG), a fluorescent molecule [(rhodamine B, RhB) or (2',7'-dichlorofluorescein sodium salt, DCF)], and a photochromic molecule [1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)-3,3,4,4,5,5-hexafluoro-1-cyclopentene, DAE], thus constructing photomodulated switchable CPL soft materials. It was found that FLG could form supramolecular gel in ethanol and self-assemble into left-handed twisted nanostructures. During the formation of a co-gel with RhB (or DCF) and DAE, the chirality of FLG could be effectively transferred to both the fluorescent and photochromic components, which induced them with chiroptical properties including CPL and circular dichroism (CD). DAE undergoes a reversible transition between the achromatous open state and the dark purple closed state in the co-gel under alternating irradiation with UV and visible light. During such a process, an intermolecular Förster resonance energy transfer (FRET) behavior from fluorescent RhB to ring-closed DAE caused the emission quenching of RhB, which led to CPL silence of RhB in the co-gel. Subsequent irradiation with visible light caused the restoration of the emission and CPL activity with the restored open state. These changes could be repeated many times upon alternate UV and visible irradiation. Therefore, a reversible CPL switch was fabricated in supramolecular gels through the photomodulated FRET process.

Ancillary ligand modulated stereoselective self-assembly of triple-stranded Eu(iii) helicate featuring circularly polarized luminescence

Creating optically pure metal assemblies is a hot research topic in the realms of chiral supramolecules. Here, three new triple-stranded europium(iii) helicates Eu₂L₃(L′)₂ [L = 4,4′-bis(4,4,4-trifluoro-1,3-dioxobutyl)diphenyl sulphide; L′ = 1,10-phenanthroline (Phen) or R/S-2,2′-bis(diphenylphosphinyl)-1,1′-binaphthyl (R/S-BINAPO)] were synthesized in order to investigate the effects of ancillary ligands on controlling the stereoselective self-assembly of lanthanide helicates. X-ray single crystal structure analysis showed that Eu₂L₃(Phen)₂ crystalized in an achiral space group P1̄ with the equivalent amount of P and M helicates in one single cell. The isolated Eu₂L₃(S-BINAPO)₂ and Eu₂L₃(R-BINAPO)₂ were verified to be enantiopure by ¹H, ¹⁹F, ³¹P NMR and DOSY NMR analyses. Additionally, the mirror-image CD spectra also demonstrated the successful syntheses of the enantiomers and the presence of an effective chirality transformation from BINAPO to achiral L. Furthermore, the perfect mirror-image circularly polarized luminescence (CPL) spectra of Eu₂L₃(S-BINAPO)₂ and Eu₂L₃(R-BINAPO)₂ indicated the existence of the excited state chirality of the Eu³⁺ center associated with |g_lum| values reaching 0.112. In addition, the photophysical properties of three helicates were also discussed.

Chiral ancillary ligands (R/S-BINAPO) modulated the stereoselective self-assembly of lanthanide helicates, which presented strong CPL with |g_lum| values up to 0.112 and high luminescence quantum yield up to 34%.

Aggregation-Induced Circularly Polarized Luminescence from Boron Complexes with a Carbazolyl Schiff Base

A variety of carbazolyl-appended Schiff bases were readily synthesized from 1-formylcarbazoles and aniline derivatives. Boron complexation of the resulting ligands allowed for facile preparation of new carbazole-based BODIPY analogues showing solid-state fluorescence. Furthermore, some dyes were converted into chiral compounds through the Et₂ AlCl-mediated incorporation of a binaphthyl unit. The chiral dyes showed aggregation-induced fluorescence and circularly polarized luminescence (CPL) with the Φ_F and g_lum of up to 0.22 and -3.5×10^-3 , respectively, in the solid state. The solid-state fluorescence and CPL were well characterized by the crystal packing analyses and DFT calculations.

Of Twists and Curves: Electronics, Photophysics, and Upcoming Applications of Non-Planar Conjugated Organic Molecules

Non-planar conjugated organic molecules (NPCOMs) contain π-conjugation across their length and also exhibit asymmetry in their conformation. In other words, certain molecular fragments in NPCOMs are either twisted or curved out of planarity. This conformational asymmetry in NPCOMs leads to non-uniform charge-distribution across the molecule, with important photophysical and electronic consequences such as altered thermodynamic stability, chemical reactivity, as well as materials properties. Majorly, NPCOMs can be classified as having either Fused or Rotatable architectures. NPCOMs have been the focus of significant scientific attention in the recent past due to their exciting photophysical behavior that includes intramolecular charge-transfer (ICT), thermally activated delayed fluorescence (TADF) and long-lived charge-separated states. In addition, they also have many useful materials characteristics such as biradical character, semi-conductivity, dynamic conformations, and mechanochromism. As a result, rational design of NPCOMs and mapping their structure-property correlations has become imperative. Researchers have executed conformational changes in NPCOMs through a variety of external stimuli such as pH, temperature, anions-cations, solvent, electric potential, and mechanical force in order to tailor their photophysical, optoelectronic and magnetic properties. Converging to these points, this review highlights the lucrative electronic features, photophysical traits and upcoming applications of NPCOMs by a selective survey of the recent scientific literature.

Electric-Field-Regulated Energy Transfer in Chiral Liquid Crystals for Enhancing Upconverted Circularly Polarized Luminescence through Steering the Photonic Bandgap

Circularly polarized luminescent materials with high dissymmetry factor (g_lum ) have been attracting increasing attention due to their distinctive photonic properties. In this work, by incorporating upconversion nanoparticles (UCNPs) and CsPbBr₃ perovskite nanocrystals (PKNCs) into a chiral nematic liquid crystal (N*LC), enhanced upconverted circularly polarized luminescence (UC-CPL) based on a radiative energy transfer (RET) process from UCNPs to CsPbBr₃ PKNCs is successfully implemented. By locating the emission peak of CsPbBr₃ PKNCs at the center of the photonic bandgap of N*LC, the maximum g_lum value of UC-CPL can be amplified to an extremely large value of 1.1. Meanwhile, upconverted emission of UCNPs can be significantly enhanced due to the band edge enhancement effect of the N*LC, subsequently enhancing the emission of the CsPbBr₃ PKNCs through the RET process. In addition, an applied electric field can switch the upconverted emission of the UCNPs, as well as the RET process, enabling an electric-field-controlled UC-CPL switch.

Self-assembly of isomeric naphthalene appended glucono derivatives: nanofibers and nanotwists with circularly polarized luminescence emission

Two isomeric naphthalene appended glucono derivatives substituted at the 1 or 2-naphthyl positions (Nap-1 and Nap-2) were designed and their self-assembly behaviors and optical properties were investigated. Nap-1 and Nap-2 were found to self-assemble into nanofibers and nanotwists, respectively. While the molecular chirality of the glucono moiety could not be effectively transferred to the naphthalene moiety in the Nap-1 system, this was achieved in the Nap-2 assembly. Thus, the Nap-2 assembly showed obvious circular dichroism (CD) and circularly polarized luminescence (CPL) signals. From the XRD patterns and IR spectra of the supramolecular assemblies, it was found that Nap-2 packed in a more orderly fashion than Nap-1, leading to a hierarchical assembly forming nanotwist structures. Moreover, a light-harvesting system based on Nap-2 supramolecular gels and dyes was established, in which an efficient energy transfer was demonstrated from Nap-2 to an acceptor Eosin Y. It was further found that both chirality and energy transfer enhanced the dissymmetry factor of Eosin Y CPL emission.

Preorganized helical chirality controlled homochiral self-assembly and circularly polarized luminescence of a quadruple-stranded Eu2L4 helicate

β-Diketones are one of the most widely used ligands for sensitizing the luminescence of lanthanide complexes due to their excellent sensitization abilities. However, the difficulties in introducing chiral groups to take part in the electronic transitions of conjugated systems limit their application in lanthanide circularly polarized luminescence (CPL) materials. In view of the inherent chirality of the helical structure, herein, a pair of homochiral quadruple-stranded helicates, Eu2L4, is assembled based on chiral bis-β-diketonate ligands, wherein the two point chirality centers in the spacer preorganize the helical conformation of the ligand (3S,4S)/(3R,4R)-3,4-bis(4,4'-bis(4,4,4-trifluoro-1,3-dioxobutyl)phenoxyl)-1-benzylpyrrolidine, LSS/LRR. X-ray crystallographic analyses reveal that the R,R configurations of the chiral carbons in the spacer induce the M helical sense of the ligand, while the S,S configurations induce the P helical sense. Through the comprehensive spectral characterization in combination with semiempirical geometry optimization using the Sparkle/RM1 model, it is confirmed that the preorganized ligands successfully control the homochirality of the helicates. Moreover, the mirror-image CD and CPL spectra and NMR measurements confirm the formation of enantiomeric pairs and their diastereopurities in solution. Detailed photophysical and chiroptical characterization studies reveal that the helicates not only exhibit intense circularly polarized luminescence (CPL) with |glum| values reaching 0.10, but also show a high luminescence quantum yield of 34%. This study effectively combines the helical chirality of the helicates with the excellent sensitization ability of the β-diketones, providing an effective strategy for the syntheses of chiral lanthanide CPL materials.

Azahelicene-Fused BODIPY Analogues Showing Circularly Polarized Luminescence

Helical carbazole-based BODIPY analogues were readily synthesized via aza[7]helicenes. The structures of azahelicene-incorporated BF₂ dyes were elucidated by x-ray diffraction analysis. DFT calculations revealed that the π-conjugated system expanded from the helicene moiety to the BODIPY framework. The azahelicene-fused boron complexes showed the Cotton effects and the circularly polarized luminescence (CPL) in the visible region. Furthermore, an axially chiral binaphthyl group was attached to the helically chiral dyes, which enhanced the chiroptical properties.

Dimension-Tunable Circularly Polarized Luminescent Nanoassemblies with Emerging Selective Chirality and Energy Transfer

The selective interplay between dimensional morphology transition and signal transfer is an important feature for both nanomaterials and biosystems. While most of those reported examples considered either dimensional transition or signal transfer, the integrated interplay or selectivity for these two aspects in single self-assembled system has been rarely studied. Here, we report that a positively charged chiral π-building block could self-assemble into multidimensional nanostructures, which showed tunable circularly polarized luminescence (CPL). Impressively, when these CPL-active multidimensional structures interacted with two achiral dyes (positively charged ThT and negatively charged CNA), 3D nanocubes and 0D nanospheres showed neither chirality transfer nor energy transfer, while 2D nanoplates could successfully trigger a selective chirality or energy transfer depending on the charge type of acceptor dyes, which then emitted an enhanced CPL signal. This work demonstrated rational design of charged π-building block for the construction of dimension controllable and selective signal transfer self-assembly system, which might deepen the understanding the interplay of dimensional structures and signal transfer functions in natural and nano systems.

Synthesis and Chiroptical Properties of Chiral Carbazole-Based BODIPYs

A series of carbazole-based boron dipyrromethenes (BODIPYs) 2 a-g bearing binaphthyl units have been synthesized by the Et₂ AlCl-mediated reaction of the corresponding BODIPY difluorides 1 a-g with 1,1'-binaphthalene-2,2'-diol. Substituents such as halogen, nitrile, and amino groups were tolerated under the reaction conditions, and the reaction of the phenylethynyl-substituted 1 h gave (R,R)-3 h bearing two binaphthyl units. The chiroptical properties of these dyes with different substituents were investigated by UV/Vis, CD, fluorescence, and circularly polarized luminescence (CPL) spectroscopy. The CD spectra showed Cotton effects in the absorption region of the BODIPY moieties. In addition, they showed CPL both in solution and in the solid state. Interestingly, several dyes recorded higher g_lum values in the solid state, probably due to intermolecular interactions. Because (R,R)-3 h recorded relatively low g_lum values, the diastereomer (R,S)-3 h was prepared. The (R,S) diastereomer showed intense CPL, which suggests a synergetic effect of the two binaphthyl groups. Finally, chiral carbazole-based BODIPY dimers have been synthesized for the first time and their chiroptical properties were investigated. They showed redshifted fluorescence and CPL, which reached the near-IR (NIR) region in the solid state.

Conformational Dynamics of Monomer- versus Dimer-like Features in a Naphthalenediimide-Based Conjugated Cyclophane

The design and synthesis of an enantiomeric pair of 1,8-diethynylanthracene-bridged naphthalenediimide (NDI)-based cyclophanes (Cyclo-NDIs) are reported. Each enantiomer of Cyclo-NDI exhibits a circularly polarized luminescence signal with a relatively large luminescence dissymmetry factor (g_lum =±8×10^-3 ). We have further investigated the modulation of through-space electronic communication between co-facially oriented NDIs in a discrete Cyclo-NDI with changes in the temperature. Tuning of the electronic communication results from the conformational transformation of monomer- versus dimer-like features of Cyclo-NDI, as confirmed by UV/Vis, fluorescence, circular dichroic, and NMR spectroscopic analysis. The temperature-dependent optical response in the Cyclo-NDI through the conformational transformation could be utilized as a highly sensitive and reversible optical thermometer in a wide temperature range (100 to -80 °C).

Multi-color tunable circularly polarized luminescence in one single AIE system

Circularly polarized luminescence (CPL) materials with a large luminescence dissymmetry factor (g_lum) and multi-color properties are very attractive. While multi-color tunable CPL can be realized by different organic dyes, the challenge of realizing both a higher g_lum and multiple colors using a single component remains. Here, we design an aggregation-induced emission (AIE) fluorophore, which is a pyridine functionalized cyanostilbene attached to a chiral unit, and realize multi-color tunable CPL with a high g_lum. The compound can self-assemble into a nanohelix and form both gel and xerogel films, exhibiting blue CPL with large g_lum values of −3.0 × 10⁻² and −1.7 × 10⁻², respectively. With the assistance of pyridine protonation, the xerogel films exhibit red-shifted CPL signals from 480 nm to 530 nm, covering from blue via green and yellow to orange. Additionally, the g_lum remains constant during the process. This work paves a simple and convenient way to construct multi-color tunable CPL materials using a single molecule.

A multi-color tunable circularly polarized luminescence (CPL) xerogel film with a large luminescence dissymmetry factor (g_lum) is achieved using a single compound upon protonation.