Axially N-Embedded Quasi-Carbon Nanohoops with Multioxidation States

The incorporation of heteroatoms into carbon nanohoops can significantly overcome aromatic stabilization energy and enrich their physicochemical properties depending on the positions and numbers of the doped atoms.Utilizing a V-shaped dipyreneo[c,e]dihydrophenazine as the building block,herein we report a novel kind of axially N-embedded quasi-carbon nanohoops by integratingπ-extended dihydropyrazine and para-phenylene subunits.Singlecrystal X-ray diffraction analyses revealed that their geometrical structures varied from droplet-shaped geometry for DPP-M and suppressed elliptical cross-section configuration for DPP-D to triangularly prismatic configuration for DPP-T.Spectroscopic measurements confirmed rich electronic properties,especially multioxidation behaviors due to the embedding of graphitic-N atoms,which are not observed in carbonaceous nanohoops and other analogs.Further investigations,including electron spin resonance spectroscopy,theoretical calculations,and single-crystal structure analyses,on the oxidized species of both DPP-D and DPP-T demonstrated their tunable open-shell ground states for the dications.This work provides a new synthetic strategy to axially N-embedded quasi-carbon nanohoops and gives insights into the design of structure-precise segments of graphitic-N-doped single-walled carbon nanotubes.

Controlling molecular assembly on time scale:Time-dependent multicolor fluorescence for information encryption

Dynamic assembly on time scale is common in biological systems but rare for artificial materials,especially for smart luminescent materials.Programming molecular assembly in a spatio-temporal manner and resulting in white-light-including multicolor fluorescence with time-dynamic features remains challenging.Herein,controlling molecular assembly on time scale is achieved by integrating a pH-responsive motif to a transient alkaline solution which is fabricated by activators(NaOH)and deactivators(esters),leading to automatic assembly on time scale and time-dependent multicolor fluorescence changing from blue to white and yellow.The kinetics of the assembly process is dependent on the ester hydrolysis process,which can be controlled by varying ester concentrations,temperature,initial pH,stirring rate and ester structures.This dynamic fluorescent system can be further developed for intelligent fluorescent materials such as fluorescent ink,three-dimension(3D)codes and even four-dimension(4D)codes,exhibiting a promising potential for information encryption.

Enhancing the deep-red/near-infrared fluorescence of higher rylene diimides via the chalcogen-annulation strategy

Deep-red/near-infrared fluorescence is highly suitable for bioimaging owing to its ability to deeply penetrate tissues,organs,and live animals.However,developing organic fluorophores with high deep-red/near-infrared fluorescence quantum yield(Φ_(FL))and fluorescent brightness remain a significant challenge owing to the energy gap law.Herein,we developed a straightforward and effective chalcogen-annulation strategy by introducing O,S and Se into the bay region of TDI and QDI fluorophores,realizing the increase ofΦFLand fluorescent brightness up to 10 times.To our best knowledge,this study potentially stands as the pioneering instance showcasing the anti-heavy-atom effect of chalcogens,and the absoluteΦFL(93%)and fluorescent brightness(128,200 cm^(-1)mol^(-1)L)of Se-TDI is among top deep-red/near-infrared organic fluorophores currently available.The femtosecond transient absorption(fs-TA)measurements show the absence of obvious changes of the excited state lifetime after the introduction of chalcogens in TDI and QDI fluorophores,indicating that intersystem crossing(ISC)can be neglected in TDI and QDI fluorophores.Theoretical calculations further reveal the chalcogen-annulation strategy increase the radiative rates and reduce the reorganization energy of several accepting modes at the ground state in TDI fluorophores,leading to the suppression of internal conversion(IC)processes.Our chalcogen-annulation strategy,which effectively increases the Φ_(FL)and restricts the IC processes,while remaining unaffected by the heavy-atom effect,offers novel insights and theoretical support for the design and synthesis of deep-red/near-infrared organic fluorophores with high Φ_(FL)and fluorescent brightness.

A Single-Fluorophore Multicolor Molecular Sensor That Visually Identifies Organic Anions Including Phosphates

Developing fluorescent sensors for small-molecule phosphates offers opportunities in optically detecting biorelevant reactions and events.However,it remains elusive how to identify phosphates from other anions,such as carboxylates and sulfates,because current synthetic phosphate receptors lack selectivity.Here we report the construction of a multicolor fluorescent sensor that can identify phosphates from other analogous anions.The key design principle is to take advantage of the highly sensitive conformation-dependent emissive wavelength of diphenyl-9,14-dihydrodibenzo[a,c]phenazine fluorophores to sense the minor structural differences between phosphates and other anions,for example,sulfates and carboxylates.The effect of structural factors such as spacer length and urea versus thiourea has been investigated by comparing the optical properties and binding affinities with the phosphate receptors.This strategy provides a simple and robust fluorescent sensing solution to optically analyze small-molecule phosphates with antiinterference performance.

Out-of-equilibrium supramolecular self-assembling systems driven by chemical fuel

A rich variety of smart materials developed via supramolecular assembly strategies have been introduced in the past decades.However,most materials reside in the thermodynamic equilibrium state,opposed to those nonequilibrium structures with sophisticated functions that are observed in living systems.To develop advanced synthetic systems,chemists have begun to focus on how to use strategies similar to those used in biological systems for fabricating artificial out-of-equilibrium systems.Heretofore,a rich variety of artificial out-of-equilibrium systems have been developed.In this review,we have summarized the recent progress of artificial out-of-equilibrium systems and categorized them in terms of the chemical fuel used,including adenosine triphosphate(ATP),acid/base,carbodiimide reagents,and many others.For these self-assembling systems,their design strategies,potential applications,as well as advantageous features have been discussed.At the end of this review,the remaining challenges and an outlook of the chemical-fuel-driven out-of-equilibrium systems were also discussed.It is believed that this review has provided some insights and could be useful for those who are interested in the out-of-equilibrium supramolecular assembling systems and their subsequent constructing strategies for various transient materials.

Highly Ordered Supramolecular Assembled Networks Tailored by Bioinspired H-Bonding Confinement for Recyclable Ion-Transport Materials

Controlling dynamic molecular self-assembly to finely tune macroscopic properties offers chemical solutions to rational material design.Here we report that combining disulfide-mediated ring-opening polymerization withβ-sheet-like H-bonding self-assembly can drive a direct small-molecular assembly into a layered ionic network with precise architectural tunability and controllable functions as ion-transport membranes.This strategy enables a one-step evaporationinduced self-assembly from discrete small molecules to layered ionic networks with high crystallinity.The interlayer distances can be readily engineered with nanometer accuracy by varying the length of the oligopeptide side chain.The synergy of the layered structure and hydrophilic terminal groups facilitates the formation and ordering of interlayer water channels,endowing the resulting membranes with high efficiency in transporting ions.Moreover,the inherent dynamic nature of poly(disulfide)s allows chemical recycling to monomers under mild conditions.We foresee that the robust strategy of combining dynamic disulfide chemistry and noncovalent assembly can afford many opportunities in designing smart materials with unique functions and applications.

Cucurbit[8]uril-mediated multi-color fluorescence system for time-dependent information encryption

Programming microscopic assembly mode to control macroscopic property is an attractive research objective.In particular,controlling molecular assembly to control fluorescence is of considerable interest for developing smart fluorescent materials.Herein,a color-tunable supramolecular emissive system was developed based on cucurbit[8]uril mediated host-guest assembly.Chemical designing for the molecular structures with minimized change resulted in different assembly modes and hence generating distinctive fluorescence,including green,yellow and orange with the addition of cucurbit[n]uril.Taking advantage of this feature,the advanced information encryption material(4D code)with multiple encryption levels and time-dependent encryption feature was developed.Such a code was dynamic on time scale,generating a series of 3D codes with time.The encrypted information only can be recognized by integrating time-coursed codes.This work provides a new insight for designing intelligent fluorescent materials for information encryption with high level of security.

Tailor-Made Dynamic Fluorophores:Precise Structures Controlling the Photophysical Properties

Organic fluorophores with dynamic conformations in the excited state have played a significant role in applications of organic functional dyes.Among them,dihydrophenazine-based dynamic fluorophores involving a photoinduced structural planarization process in the excited state exhibited large Stokes shifts and conformation-dependent multicolor emissions.With the developments of synthetic strategies,precise modifications on dihydrophenazinebased scaffolds have successfully afforded a variety of precise molecular structures of varying sizes and compositions,which have delicately modulated their photophysical properties.Herein,this Perspective summarizes the precise modulations of dihydrophenazine-based dynamic fluorophores,including the development of the synthetic methodologies,and tailor-made molecular models to reveal the luminescence−structure relationships.

Recent advances in new-type molecular switches

Molecular switches that can undergo reversible switching between two or more different states in response to external stimuli have been used in the fabrication of various optoelectronic devices and smart materials for many decades, and also found many applications in sensing, molecular self-assembly and photo-controlled biological systems. Recently, mechanically interlocked molecules, such as rotaxanes and catenanes, and molecular rotary motors based on overcrowded alkenes have emerged as two new kinds of molecular switches. Some novel applications of above-mentioned molecular switches have been discovered. In this mini review, we mainly highlight noticeable achievements over the past decade in this field, and summarize the applications of new types of molecular switches, for instance, controlling the chiral space to regulate catalytic reaction as organocatalysts, controlling molecular motions, synthesizing a peptide in a sequence-specific manner and modulating the wettability of the self-assembled monolayers.

Visualizing Aβdeposits in live young AD model mice with a simple red/near-infrared-fluorescent AIEgen

Precise and early detection ofβ-amyloid(Aβ)deposits in situ and in real time is pivotal to the diagnosis and early intervention of Alzheimer’s disease(AD).Optical imaging stands out to be a promising technique for such a task;however,it still remains a big challenge,due to the lack of high-performance imaging contrast agent.Restricted by poor blood-brain barrier(BBB)penetrability,short-wavelength excitation and emission,as well as the aggregation-caused quenching effect,the widely used goldstandard probes cannot be used for early in-vivo imaging of Aβdeposits.Herein,we integrate the Aβdeposits-favored geometry,amphiphilic and zwitterionic molecular structure,extended D-π-A electronic structure,and 3 D conformation into one molecule,facilely establishing a simple and economic imaging contrast agent that enjoys high specificity and affinity to Aβdeposits,good BBB penetrability,bright red/near-infrared fluorescence,low interference from autofluorescence,aggregation-induced emission(AIE)feature,high signal-to-noise ratio(SNR),and high contrast.In-vitro,ex-vivo,and in-vivo experiments with different strains of mice indicate that AIE-CNPy-AD holds the universality to Aβdeposits identification.Noteworthily,AIE-CNPy-AD is even able to precisely trace the small and sparsely-distributed Aβdeposits in AD model mice as young as 4-month-old APP/PS1 mice,the youngest having Aβdeposits.Moreover,the present probe could clearly reveal the increase and enlargement of Aβdeposits as the mice grow.Therefore,AIE-CNPy-AD might be an ideal alternative for early AD diagnosis and highly reliable monitoring of AD progression.

Optically probing molecular shuttling motion of[2]rotaxane by a conformation-adaptive fluorophore

A bistable[2]rotaxane with a conformation-adaptive macrocycle bearing a 9,14-diphenyl-9,14-dihydrodibenzo[a,c]phenazine(DPAC)unit was synthesized,which could be utilized to optical probe the molecular shuttling motion of the functionalized rotaxane system.The UV-vis,^(1) H NMR and PL spectroscopic data clearly demonstrated that the DPAC ring was interlocked onto the thread and the fluorescence intensity of the DPAC unit in the macrocycle was effectively regulated by the location change of the macrocycle along the thread under acid/base stimulation,which was attributed to the modulation of the intramolecular photo-induced electron transfer between the DPAC unit and the methyltriazole(MTA)unit.This bistable rotaxane system containing a conformation-adaptive fluorophore unit in the macrocycle moiety opens an alternative way to design functional bistable mechanically interlocked molecules.

Vibratile Dihydrophenazines with Controllable Luminescence Enabled by Precise Regulation of π-Conjugated Wings

A series of vibratile π-extended dihydrophenazines(BPs)and a tetrahydrodiphenazine(TP)were synthesized via direct C-N coupling reactions.Structural alterations of the fused acene wings lead to diverse intermolecular packing arrangements as well as tunable photophysical properties.These compounds exhibit intriguing features,including large Stokes shift,multiple emissions,and environmental effects.Notably,a dramatic hypsochromic shift in emission is observed when the acene wing is linearly extended from benzene to naphthalene and anthracene.This unusual π-conjugation length-dependent emission is explained by the close correlation between the calculated fluorescence-emitting energy and the π-conjugation length of the acene subunit.In addition,the TP bearing two flexible units exhibits dynamic photophysical properties resembling those of BPs.Our results reveal a balanced control over π-conjugation and luminescence in vibratile π-systems,thereby providing new insight into the molecular design of organic near-infrared fluorophores with large Stokes shifts and dynamic emissions.

Constructing supramolecular polymers from phototrigger containing monomer

A new type of photo-induced supramolecular polymer was fabricated by host-guest interaction from a phototrigger containing building block. A dibenzo-24-crown-8 （DB24C8） macrocycle and dibenzylammonium （DBA） site containing linear monomer was designed and synthesized. The coumarin, as a photocleavable protector, was introduced to the terminal of the monomer. When exposed to the UV light, the coumarin unit would be cleavaged and the monomer without terminal coumarin can self-assemble into supramolecular polymers via the host-guest interaction between DB24C8 moieties and DBA units. Increasing the concentration of the monomer, the supramolecular polymers will convert to supramolecular organogel by cross-linking with each other.

Visible Light-Induced Collapse of Molecular Microcrystals into Droplets by E-to-Z Photoisomerization and Melting Phase Transition

Harnessing photoresponsive behavior in organic crystals,such as shape and morphology deformation,on multiple scales is intriguing with respect to precise spatiotemporal operation,because dynamic deformations are promising in fabricating future intelligent devices.Here,we synthesized a new photoresponsive molecular crystal composed of dimethyl(E)-2-(3-(naphthalen-1-yl)allylidene)malonate((E)-DNAM)that undergoes E-to-Z photoisomerization accompanied by photoinduced crystal-to-liquid melting phase transition when exposed to visible light.Instead of expanding in bulk polycrystals,single-crystal(E)-DNAM rectangular microplates in an aqueous solution rapidly collapsed into liquid droplets,showing a remarkable drastic reduction in surface area of more than 97%after light illumination.We deduce that the unique microscopic morphology of microplates with high aspect ratios of length-tothickness reaching up to 1000 is mainly responsible for the photoinduced melting leading to drastic collapse.In addition,the cohesive forces of liquid photoproduct facilitate the overall deformations and transformation.We have shown a facile way to achieve the remarkable collapse of molecular crystals into droplets by photochemical reaction and phase transition.