Dynamic Timing Control over Multicolor Molecular Emission by Temporal Chemical Locking

Advancing Dynamic Polymer Mechanochemistry through Synergetic Conformational Gearing

Harnessing mechanical force to modulate material properties and enhance biomechanical functions is essential for advancing smart materials and bioengineering. Polymer mechanochemistry provides an emerging toolkit for exploring unconventional chemical transformations and modulating molecular structures through mechanical force. One of the key challenges is developing innovative force-sensing mechanisms for precise and in situ force detection. This study introduces mDPAC, a dynamic and sensitive mechanophore, demonstrating its mechanochromic properties through synergetic conformational gearing. Its unique mechanoresponsive mechanism is based on the simultaneous conformational synergy between its phenazine and phenyl moieties, facilitated by a worm-gear-like structure. We confirm mDPAC's complex mechanochemical response and elucidate its mechanotransduction mechanism through our experimental data and comprehensive simulations. The compatibility of mDPAC with hydrogels is particularly notable, highlighting its potential for applications in aqueous biological environments as a dynamic force sensor. Moreover, mDPAC's multicolored mechanochromic responses facilitate direct force sensing and visual detection, paving the way for precise and real-time mechanical force sensing in bulk materials.

Monofluorophore-based Two-Photon Ratiometric Fluorescent Probe for the Quantitative Imaging of Fatty Acid Amide Hydrolase in Live Neurons and Mouse Brain Tissues

Fatty acid amide hydrolase (FAAH) plays a crucial role in the metabolism of the endocannabinoid system by hydrolyzing a series of bioactive amides, whose abnormal levels are associated with neuronal disorders including Alzheimer's disease (AD). However, due to the lack of suitable quantitative sensing tools, real-time and accurate monitoring of the activity of FAAH in living systems remains unresolved. Herein, a novel enzyme-activated near-infrared two-photon ratiometric fluorescent probe (CANP) based on a naphthylvinylpyridine monofluorophore is successfully developed, in which the electron-withdrawing amide moiety is prone to be hydrolyzed to an electron-donating amine group under the catalysis of FAAH, leading to the activation of the intramolecular charge transfer process and the emergence of a new 80 nm red-shifted emission, thereby achieving a ratiometric luminescence response. Benefiting from the high selectivity, high sensitivity, and ratiometric response to FAAH, the probe CANP is successfully used to quantitatively monitor and image the FAAH levels in living neurons, by which an amyloid β (Aβ)-induced upregulation of endogenous FAAH activity is observed. Similar increases in FAAH activity are found in various brain regions of AD model mice, indicating a potential fatty acid amide metabolite-involved pathway for the pathological deterioration of AD. Moreover, our quantitative FAAH inhibition experiments further demonstrate the great value of CANP as an efficient visual probe for in situ and precise assessment of FAAH inhibitors in complex living systems, assisting the discovery of FAAH-related therapeutic agents.

Multiple photofluorochromic luminogens via catalyst-free alkene oxidative cleavage photoreaction for dynamic 4D codes encryption

Controllable photofluorochromic systems with high contrast and multicolor in both solutions and solid states are ideal candidates for the development of dynamic artificial intelligence. However, it is still challenging to realize multiple photochromism within one single molecule, not to mention good controllability. Herein, we report an aggregation-induced emission luminogen TPE-2MO2NT that undergoes oxidation cleavage upon light irradiation and is accompanied by tunable multicolor emission from orange to blue with time-dependence. The photocleavage mechanism revealed that the self-generation of reactive oxidants driving the catalyst-free oxidative cleavage process. A comprehensive analysis of TPE-2MO2NT and other comparative molecules demonstrates that the TPE-2MO2NT molecular scaffold can be easily modified and extended. Further, the multicolor microenvironmental controllability of TPE-2MO2NT photoreaction within polymer matrices enables the fabrication of dynamic fluorescence images and 4D information codes, providing strategies for advanced controllable information encryption.

Multimode Stimuli-Responsive Room-Temperature Phosphorescence Achieved by Doping Butterfly-like Fluorogens into Crystalline Small-Molecular Hosts

Materials with stimuli-responsive purely organic room-temperature phosphorescence (RTP) exempt from exquisite molecular design and complex preparation are highly desirable but still relatively rare. Moreover, most of them work in a single switching mode. Herein, we employ a versatile host-guest-doped strategy to facilely construct efficient RTP systems with multimode stimuli-responsiveness without ingenious molecular design. By conveniently doping butterfly-like guests, namely, N,N'-diphenyl-dihydrodibenzo[a,c]phenazines (DPACs), featured with vibration-induced emission into the small-molecular hosts via various methods, RTP systems with finely tunable photophysical properties are readily obtained. Through systematic mechanistic studies and with the aid of a series of control experiments, we unveil the critical role of the host crystallinity in achieving efficient RTP. By virtue of the inherent environmental sensitivity of both RTP and fluorescence of the DPACs, our systems exhibit multiple-stimuli-responsiveness with the luminescence not only switching between the fluorescence and phosphorescence but also continuously changing in the fluorescence color. Advanced dynamic anticounterfeiting and multilevel information encryption is thereby realized.

Tuning vibration-induced emission through macrocyclization and catenation

In order to investigate the effect of macrocyclization and catenation on the regulation of vibration-induced emission (VIE), the typical VIE luminogen 9,14-diphenyl-9,14-dihydrodibenzo[a, c]phenazine (DPAC) was introduced into the skeleton of a macrocycle and corresponding [2]catenane to evaluate their dynamic relaxation processes. As investigated in detail by femtosecond transient absorption (TA) spectra, the resultant VIE systems revealed precisely tunable emissions upon changing the solvent viscosity, highlighting the key effect of the formation of [2]catenane. Notably, the introduction of an additional pillar[5]arene macrocycle featuring unique planar chirality endows the resultant chiral VIE-active [2]catenane with attractive circularly polarized luminescence in different states. This work not only develops a new strategy for the design of new luminescent systems with tunable vibration induced emission, but also provides a promising platform for the construction of smart chiral luminescent materials for practical applications.

Dual-Mode Hydrogels with Structural and Fluorescent Colors toward Multistage Secure Information Encryption

Constructing an anti-counterfeiting material with non-interference dual optical modes is an effective way to improve information security. However, it remains challenging to achieve multistage secure information encryption due to the limited stimulus responsiveness and color tunability of the current dual-mode materials. Herein, a dual-mode hydrogel with both independently tunable structural and fluorescent colors toward multistage information encryption, is reported. In this hydrogel system, the rigid lamellar structure of poly(dodecylglyceryl itaconate) (pDGI) formed by shear flow-induced self-assembly provides the restricted domains wherein monomers undergo polymerization to form a hydrogel network, producing structural color. The introduction of fluorescent monomer 6-acrylamidopicolinate (6APA) as a complexation site provides the possibility of fluorescent color formation. The hydrogel's angle-dependent structural color can be controlled by adjusting the crosslinking density and water content. Additionally, the fluorescence color can be modulated by adjusting the ratio of lanthanide ions. Information of dual-mode can be displayed separately in different channels and synergistically overlayed to read the ultimate message. Thus, a multistage information encryption system based on this hydrogel is devised through the programed decryption process. This strategy holds tremendous potential as a platform for encrypting and safeguarding valuable and authentic information in the field of anti-counterfeiting.

Chemically fueled dynamic switching between assembly-encoded emissions

Self-assembly provides access to non-covalently synthesized supramolecular materials with distinct properties from a single building block. However, dynamic switching between functional states still remains challenging, but holds enormous potential in material chemistry to design smart materials. Herein, we demonstrate a chemical fuel-mediated strategy to dynamically switch between two distinctly emissive aggregates, originating from the self-assembly of a naphthalimide-appended peptide building block. A molecularly dissolved building block shows very weak blue emission, whereas, in the assembled state (Agg-1), it shows cyan emission through π stacking-mediated excimer emission. The addition of a chemical fuel, ethyl-3-(3-(dimethylamino)propyl)carbodiimide (EDC), converts the terminal aspartic acid present in the building block to an intra-molecularly cyclized anhydride in situ forming a second aggregated state, Agg-2, by changing the molecular packing, thereby transforming the emission to strong blue. Interestingly, the anhydride gets hydrolyzed gradually to reform Agg-1 and the initial cyan emission is restored. The kinetic stability of the strong blue emissive aggregate, Agg-2, can be regulated by the added concentration of the chemical fuel. Moreover, we expand the scope of this system within an agarose gel matrix, which allows us to gain spatiotemporal control over the properties, thereby producing a self-erasable writing system where the chemical fuel acts as the ink.

Dual Stimuli-Responsive [2]Rotaxanes with Tunable Vibration-Induced Emission and Switchable Circularly Polarized Luminescence

Aiming at the construction of novel stimuli-responsive fluorescent system with precisely tunable emissions, the typical 9,14-diphenyl-9,14-dihydrodibenzo[a, c]phenazine (DPAC) luminogen with attractive vibration-induced emission (VIE) behavior has been introduced into [2]rotaxane as a stopper. Taking advantage of their unique dual stimuli-responsiveness towards solvent and anion, the resultant [2]rotaxanes reveal both tunable VIE and switchable circularly polarized luminescence (CPL). Attributed to the formation of mechanical bonds, DPAC-functionalized [2]rotaxanes display interesting VIE behaviors including white-light emission upon the addition of viscous solvent, as evaluated in detail by femtosecond transient absorption (TA) spectra. In addition, ascribed to the regulation of chirality information transmission through anion-induced motions of chiral wheel, the resolved chiral [2]rotaxanes reveal unique switchable CPL upon the addition of anion, leading to significant increase in the dissymmetry factors (glum ) values with excellent reversibility. Interestingly, upon doping the chiral [2]rotaxanes in stretchable polymer, the blend films reveal remarkable emission change from white light to light blue with significant 6.5-fold increase in glum values up to -0.035 under external tensile stresses. This work provides not only a new design strategy for developing molecular systems with fluorescent tunability but also a novel platform for the construction of smart chiral luminescent materials for practical use.

Modulation of Heterotypic and Homotypic Interactions to Visualize the Evolution of Organic Aggregates in a Fluorescence Turn-on Manner

The abnormal evolution of membrane-less organelles into amyloid fibrils is a causative factor in many neurodegenerative diseases. Fundamental research on evolving organic aggregates is thus instructive for understanding the root causes of these diseases. In-situ monitoring of evolving molecular aggregates with built-in fluorescence properties is a reliable approach to reflect their subtle structural variation. To increase the sensitivity of real-time monitoring, we presented organic aggregates assembled by TPAN-2MeO, which is a triphenyl acrylonitrile derivative. TPAN-2MeO showed a morphological evolution with distinct turn-on emission. Upon rapid nanoaggregation, it formed non-emissive spherical aggregates in the kinetically metastable state. Experimental and simulation results revealed that the weak homotypic interactions between the TPAN-2MeO molecules liberated their molecular motion for efficient non-radiative decay, and the strong heterotypic interactions between TPAN-2MeO and water stabilized the molecular geometry favorable for the non-fluorescent state. After ultrasonication, the decreased heterotypic interactions and increased homotypic interactions acted synergistically to allow access to the emissive thermodynamic equilibrium state with a decent photoluminescence quantum yield (PLQY). The spherical aggregates were eventually transformed into micrometer-sized blocklike particles. Under mechanical stirring, the co-assembly of TPAN-2MeO and Pluronic F-127 formed uniform fluorescent platelets, inducing a significant enhancement in PLQY. These results decipher the stimuli-triggered structural variation of organic aggregates with concurrent sensitive fluorescence response and pave the way for a deep understanding of the evolutionary events of biogenic aggregates.

Self-assembly of conformation-adaptive dihydrophenazine-based coordination cages

In this study, we designed and synthesized three conformation-adaptive Pd2L4- and Pd3L6-type coordination cages based on three dihydrophenazine-based ligands with different lengths. Interestingly, the shorter ligands L1 and L2 self-assembled into Pd2L4-type coordination cages while the longer ligand L3 formed Pd3L6-type one, mainly driven by the anion template effect. All coordination cages were confirmed through single-crystal X-ray diffraction, and their structural conformations underwent great changes compared with those of their corresponding ligands. Moreover, the conformational changes also significantly affected their photophysical and electrochemical properties which were distinct from their parent ligands.

Modulating the Luminescence, Photosensitizing Properties, and Mitochondria-Targeting Ability of D-π-A-Structured Dihydrodibenzo[a,c]phenazines

Herein, pyridinium and 4-vinylpyridinium groups are introduced into the VIE-active N,N'-disubstituted-dihydrodibenzo[a,c]phenazines (DPAC) framework to afford a series of D-π-A-structured dihydrodibenzo[a,c]phenazines in consideration of the aggregation-benefited performance of the DPAC module and the potential mitochondria-targeting capability of the resultant pyridinium-decorated DPACs (DPAC-PyPF6 and DPAC-D-PyPF6). To modulate the properties and elucidate the structure-property relationship, the corresponding pyridinyl/4-vinylpyridinyl-substituted DPACs, i.e., DPAC-Py and DPAC-D-Py, are designed and studied as controls. It is found that the strong intramolecular charge transfer (ICT) effect enables the effective separation of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of DPAC-PyPF6 and DPAC-D-PyPF6, which is conducive to the generation of ROS. By adjusting the electron-accepting group and the π-bridge, the excitation, absorption, luminescence, photosensitizing properties as well as the mitochondria-targeting ability can be finely tuned. Both DPAC-PyPF6 and DPAC-D-PyPF6 display large Stokes shifts (70-222 nm), solvent-dependent absorptions and emissions, aggregation-induced emission (AIE), red fluorescence in the aggregated state (λem = 600-650 nm), aggregation-promoted photosensitizing ability with the relative singlet-oxygen quantum yields higher than 1.10, and a mitochondria-targeting ability with the Pearson coefficients larger than 0.85. DPAC-D-PyPF6 shows absorption maximum at a longer wavelength, slightly redder fluorescence and better photosensitivity as compared to DPAC-PyPF6, which consequently leads to the higher photocytotoxicity under the irradiation of white light as a result of the larger π-conjugation.

Reversible Inversion of Circularly Polarized Luminescence in a Coassembly Supramolecular Structure with Achiral Sulforhodamine B Dyes

The dynamic control of circularly polarized luminescence (CPL) has far-reaching significance in optoelectronics, information storage, and data encryption. Herein, we reported the reversible inversion of CPL in a coassembly supramolecular system consisting of chiral molecules L4, which contain two positively charged viologen units, and achiral ionic surfactant sodium dodecyl sulfate (SDS) by introducing achiral sulforhodamine B (SRB) dye molecules. The chirality of CPL in the coassemblies can be efficiently regulated and inverted by simply adjusting the amount of SRB. A series of experimental characterization, including optical spectroscopy, electron microscope, ¹H NMR, and X-ray scattering measurements, suggested that SRB could coassemble with L4/SDS to establish a new stable L4/SDS/SRB supramolecular structure through electrostatic interactions. Moreover, the negative-sign CPL could revert to the positive-sign CPL if titanium dioxide (TiO₂) nanoparticles were used to decompose SRB molecules. The evolution of the CPL inversion process could be cycled at least 5 times without a significant decline in CPL signals when SRB was refueled to the system. Our results provide a facile approach to dynamically regulating the handedness of CPL in a multiple-component supramolecular system via achiral species.

Metallophilic Interaction-Mediated Hierarchical Assembly and Temporal-Controlled Dynamic Chirality Inversion of Metal-Organic Supramolecular Polymers

The study of dynamic supramolecular chirality inversion (SMCI) not only helps to deepen the understanding of chiral transfer and amplification in both living organizations and artificially chemical self-assembly systems but also is useful for the development of smart chiral nanomaterials. However, it is still challenging to achieve the dynamic SMCI of the self-aggregation of metal-organic supramolecular polymers with great potential in asymmetric synthesis, chiroptical switches, and circular polarized luminescence. Here, we successfully developed a hierarchical coassembly system based on the mPAzPCC and various metal ions with effective chirality transfer and temporal-controlled SMCI. Due to the dynamic self-assembly and hierarchical chirality transfer of the Ag⁺/mPAzPCC complex driven by metallophilic interaction and coordination, morphological transition with nanoribbons, helical nanoribbons, and chiral nanotubules was successively obtained. Interestingly, the SMCI of chiral nanoaggregates was precisely regulated by solvents and metal ions in the Cu²⁺/mPAzPCC and Mn²⁺/mPAzPCC system. Besides, temporal-controlled dynamic SMCI switching from helix to bundled helix was clearly revealed in the aggregation of Cu²⁺/mPAzPCC, Mn²⁺/mPAzPCC, and Bi³⁺/mPAzPCC systems. This work provides a metallophilic interaction-mediated helical assembly pathway to dynamically modulate the chirality of metal-organic complex-based assemblies and deepen the understanding of the hierarchically dynamic self-assembly process, which would be of great potential in metal ion-mediated supramolecular asymmetric catalysis and bioinspired chiral sensing.

Doping of charge-transfer molecules in cocrystals for the design of materials with novel piezo-activated luminescence

A novel piezo-activated luminescent material with wide range modulation of the luminescence wavelength and a giant intensity enhancement upon compression was prepared using a strategy of molecular doping. The doping of THT molecules into TCNB-perylene cocrystals results in the formation of a weak but pressure-enhanced emission center in the material at ambient pressure. Upon compression, the emissive band from the undoped component TCNB-perylene undergoes a normal red shift and emission quenching, while the weak emission center shows an anomalous blue shift from 615 nm to 574 nm and a giant luminescence enhancement up to 16 GPa. Further theoretical calculations show that doping by THT could modify intermolecular interactions, promote molecular deformation, and importantly, inject electrons into the host TCNB-perylene upon compression, which contributes to the novel piezochromic luminescence behavior. Based on this finding, we further propose a universal approach to design and regulate the piezo-activated luminescence of materials by using other similar dopants.

A Dynamic Supramolecular H-bonding Network with Orthogonally Tunable Clusteroluminescence

Enabling dynamically tunable emissive systems offers opportunities for constructing smart materials. Clusteroluminescence, as unconventional luminescence, has attracted increasing attention in both fundamental and applied sciences. Herein, we report a supramolecular poly(disulfides) network with tunable clusteroluminescence. The reticular H-bonds synergize the rigidity and mobility of dynamic networks, and endow the resulting materials with mechanical adaptivity and robustness, simultaneously enabling efficient clusteroluminescence and phosphorescence at 77 K. Orthogonally tunable luminescence are achieved in two manners, i.e., slow backbone disulfide exchange and fast side-chain metal coordination. Further exploration of the reprocessability and chemical closed-loop recycling of intrinsic dynamic networks for sustainable materials is feasible. We foresee that the synergistic strategy of dynamic chemistry offers a novel pathway and potential opportunities for smart emissive materials.

Controlled Supramolecular Self-Assembly Pathways by Intramolecular Rotation of D-A Molecular System toward the Signal Differentiation Detection of Toxic Vapors

Revealing the structural evolution mechanisms of supramolecular self-assembly can facilitate the exploitation of new self-assembly pathways and various functional materials. Here, this work reports a unique intramolecular rotation-induced structural evolution of supramolecular assemblies from a metastable state to a thermodynamically stable state using a twisting D-A molecule. These self-assemblies are applied to the signal differentiation detection of toxic dimethylsulfide (DMS) vapors. The F₁₆₁ BT monomer of the inactive state is trapped in off-pathway metastable nanospheres, which can disassemble and induce the transformation of the F₁₆₁ BT monomer into an active state by crossing the energy barrier. Subsequently, the active monomer goes through the processes of nucleation and elongation, forming thermodynamically stable on-pathway microribbons. Adding seeds can accelerate the molecular conformational transformation, generating microribbons with controlled lengths. Opposite fluorescent responses are obtained when exposing the two aggregates to the DMS vapors, allowing the sensitive detection of DMS with enhanced selectivity, which offers tremendous potential in practical applications.

Dynamic Timing Control of Molecular Photoluminescent Systems

Dynamic control of molecular photoluminescence offers chemical solutions to designing functional emissive materials. Although stimuli-switchable molecular luminescent systems are well established, how to encode these dynamic emissive systems with a "timing" feature, that is, time-dependent luminescent properties, remains challenging. This Concept aims to summarize the design principles of dynamic timing molecular photoluminescent systems by discussing the state-of-the-art of this topic and the shaping of fabrication strategies at both the molecular and supramolecular levels. An outlook and perspectives are given to outline the future opportunities and challenges in the rational design and potential applications of these smart emissive systems.

Multicolor emission based on a N, N'-Disubstituted dihydrodibenzo [a, c] phenazine crown ether macrocycle

Dynamic fluorophore 9,14-diphenyl-9,14-dihydrodibenzo[a,c]phenazine (DPAC) affords a new platform to produce diverse emission outputs. In this paper, a novel DPAC-containing crown ether macrocycle D-6 is synthesized and characterized. Host-guest interactions of D-6 with different ammonium guests produced a variety of fluorescence with hypsochromic shifts up to 130 nm, which are found to be affected by choice of solvent or guest and host/guest stoichiometry. Formation of supramolecular complexes were confirmed by UV-vis titration, ¹H NMR and HRMS spectroscopy.

A Ribonucleotide ↔ Phosphoramidate Reaction Network Optimized by Computer-Aided Design

A growing number of out-of-equilibrium systems have been created and investigated in chemical laboratories over the past decade. One way to achieve this is to create a reaction cycle, in which the forward reaction is driven by a chemical fuel and the backward reaction follows a different pathway. Such dissipative reaction networks are still relatively rare, however, and most non-enzymatic examples are based on the carbodiimide-driven generation of carboxylic acid anhydrides. In this work, we describe a dissipative reaction network that comprises the chemically fueled formation of phosphoramidates from natural ribonucleotides (e.g., GMP or AMP) and phosphoramidate hydrolysis as a mild backward reaction. Because the individual reactions are subject to a multitude of interconnected parameters, the software-assisted tool “Design of Experiments” (DoE) was a great asset for optimizing and understanding the network. One notable insight was the stark effect of the nucleophilic catalyst 1-ethylimidazole (EtIm) on the hydrolysis rate, which is reminiscent of the action of the histidine group in phosphoramidase enzymes (e.g., HINT1). We were also able to use the reaction cycle to generate transient self-assemblies, which were characterized by dynamic light scattering (DLS), confocal microscopy (CLSM), and cryogenic transmission electron microscopy (cryo-TEM). Because these compartments are based on prebiotically plausible building blocks, our findings may have relevance for origin-of-life scenarios.

Conformationally Confined Emissive Cationic Macrocycle with Photocontrolled Organelle-Specific Translocation

The optimization of molecular conformation and aggregation modes is of great significance in creation of new luminescent materials for biochemical research and medical diagnostics. Herein, a highly emissive macrocycle (1) is reported, which is constructed by the cyclization reaction of triphenylamine with benzyl bromide and exhibits very distinctive photophysical performance both in aqueous solution and the solid state. Structural analysis reveals that the 1 can form self-interpenetrated complex and emit bright yellow fluorescence in the crystal lattice. The distorted yet symmetrical structure can endow 1 with unique two-photon absorption property upon excitation by near-infrared light. Also, 1 can be utilized as an efficient photosensitizer to produce singlet oxygen (¹ O₂ ) both in inanimate milieu and under cellular environment. More intriguingly, due to the strong association of 1 with negatively charged biomacromolecules, organelle-specific migration is achieved from lysosome to nucleus during the ¹ O₂ -induced cell apoptosis process. To be envisaged, this conformationally confined cationic macrocycle with photocontrolled lysosome-to-nucleus translocation may provide a feasible approach for in situ identifying different biospecies and monitoring physiological events at subcellular level.

Triphenylamine, Carbazole or Tetraphenylethylene-Functionalized Benzothiadiazole Derivatives: Aggregation-Induced Emission (AIE), Solvatochromic and Different Mechanoresponsive Fluorescence Characteristics

The development of mechanochromic fluorophors with high-brightness, solid-state fluorescence is very significant and challenging. Herein, highly solid-state emissive triphenylamine, carbazole and tetraphenylethylene-functionalized benzothiadiazole derivatives were developed. These compounds showed remarkable aggregation-induced emission and solvatochromic fluorescence characteristics. Furthermore, these fluorogenic compounds also displayed different mechanically triggering fluorescence responses.

A dynamic assembly-induced emissive system for advanced information encryption with time-dependent security

The development of advanced materials for information encryption with time-dependent features is essential to meet the increasing demand on encryption security. Herein, smart materials with orthogonal and temporal encryption properties are successfully developed based on a dynamic assembly-induced multicolour supramolecular system. Multicolour fluorescence, including blue, orange and even white light emissions, is achieved by controlling the supramolecular assembly of pyrene derivatives by tailoring the solvent composition. By taking advantage of the tuneable fluorescence, dynamically controlled information encryption materials with orthogonal encryption functions, e.g., 3D codes, are successfully developed. Moreover, time-dependent information encryption materials, such as temporal multi-information displays and 4D codes, are also developed by enabling the fluorescence-controllable supramolecular system in the solid phase, showing multiple pieces of information on a time scale, and the correct information can be identified only at a specified time. This work provides an inspiring point for the design of information encryption materials with higher security requirements.

Photoconductance from the Bent-to-Planar Photocycle between Ground and Excited States in Single-Molecule Junctions

Single-molecule conductance measurements for 9,14-diphenyl-9,14-dihydrodibenzo[a,c]phenazine (DPAC) may offer unique insight into the bent-to-planar photocycle between the ground and excited states. Herein, we employ DPAC derivative DPAC-SMe as the molecular prototype to fabricate single-molecule junctions using the scanning tunneling microscope break junction technique and explore photoconductance dependence on the excited-state structural/electronic changes. We find up to ∼200% conductance enhancement of DPAC-SMe under continuous 340 nm light irradiation than that without irradiation, while photoconductance disappears in the case where structural evolution of the DPAC-SMe is halted through macrocyclization. The in situ conductance modulation as pulsed 340 nm light irradiation is monitored in the DPAC-SMe-based junctions alone, suggesting that the photoconductance of DPAC-SMe stems from photoinduced intramolecular planarization. Theoretical calculations reveal that the photoinduced structural evolution brings about a significant redistribution of the electron cloud density, which leads to the appearance of Fano resonance, resulting in enhanced conductance through the DPAC-SMe-fabricated junctions. This work provides evidence of bent-to-planar photocycle-induced conductance differences at the single-molecule level, offering a tailored approach for tuning the charge transport characteristics of organic photoelectronic devices.