Digital Information Processing in Molecular Systems

Beyond Photochromism: Alternative Stimuli to Trigger Diarylethenes Switching

Diarylethenes (DAEs) are typical photochemically reversible type (P-type) photochromic materials with excellent thermal stability and high fatigue resistance and are widely exploited as photo-switches for various applications in molecular devices, data storage, photoresponsive materials, and bioimaging, etc. In recent years, there is an increasing number of reports using heat, acid, electrochemistry, etc. to drive the isomerization reaction of DAEs. The response to two or more different stimuli enables multi-functionality within a single DAE molecule, which would facilitate complex logic-gate operations, multimode data storage, and increased information density. Herein, the recent advances in DAE systems utilizing stimuli "beyond photo" to trigger the isomerization processes from three perspectives: acidochromism, thermochromism, and electrochromism are reviewed. Emphasis is placed on the molecule design strategies and the underlying mechanisms for cyclization and cycloreversion processes addressed by the alternative stimulus. Then the noticeable applications made in multi-stimuli responsive DAE systems are summarized. Additionally, the challenges and opportunities of DAE switches driven by stimuli "beyond photo" in the future are also discussed.

Kombucha-Proteinoid Crystal Bioelectric Circuits

We propose "kombucha-proteinoid crystal bioelectric circuits" as a sustainable bio-computing platform. These circuits are hybrid biological-inorganic devices that utilize crystal growth dynamics as the physical substrate to convert information. Microfluidic prototypes couple custom-synthesized thermal proteinoids within kombucha cellulose matrices and metastable calcium carbonate solutions. This bio-mineral configuration examines if precision modulation of crystal growth rates could instantiate reconfigurable logic gates for unconventional computing applications. Programming organic acid secretions allows for the adjustment of biotic-mineral polarity, thereby establishing microbial-synthetic pairings that consistently regulate the crystal growth rate of calcite deposition. By coordinating intrinsic physicochemical phenomena, accrued mineral densities literally crystallize additive/multiplicative operations via Boolean AND/OR logics. An additional way to generate structured logics similar of neural assemblies is by chaining modular crystallizer units. Proteinoid-guided carbonate crystallization may prove to be a viable material platform for unconventional computing-green, self-organizing, scalable architectures grown directly from solution-pending definitive affirmation of proof-of-concept.

Styrylbenzoquinoline dyads as a new type of fluorescing photochromes operating via [2 + 2] photocycloaddition mechanism: Optimization of the structure

We synthesized and studied a novel bichromophoric dyad in which bridging methylene groups link two styrylbenzo[f]quinoline (SBQ) photochromes to a salicylic acid residue. The dyad was designed for use as a fluorescent P-type photochrome acting via a [2 + 2] photocycloaddition (PCA) reaction. Compared to previously studied dyads, a change in the attachment handle and shortening of the bridging groups resulted in simultaneous rise of the quantum yields of both fluorescence and PCA. Under light irradiation, two competitive reversible reactions occurred in the dyad. The first is photoisomerization between the trans- and cis- isomers of the SBQ moieties. The second is PCA. The latter process was predominant and resulted in the formation of the cyclobutane ring bearing two benzo[f]quinoline (BQ) groups. In the ground S0 state, NMR data and DFT calculations indicated the formation of folded dyad conformers whose structure is pre-organized for PCA due to π-stacking interactions of two SBQ moieties. In the excited dyad, steady-state and time-resolved nanosecond fluorescence spectroscopy revealed the formation of an excimer, which was assumed to be a precursor of cyclobutane. Due to the fluorescence properties of SBQ and BQ, both dyad and cyclobutane fluoresce and can serve as a color-correlated multicolor fluorescence photoswitch. A simple approach is proposed for predicting the relationship between the spectral properties of the dyad and cyclobutane, which are the open and closed isomers of a new type of photochromes. The approach uses the dependence of the position of the maximum of the absorption band of an aromatic compound on the size of the π-system, as well as the fact that the sizes of the π-systems of the dyad and cyclobutane are related by a simple relation.

Spin crossover iron complexes with spin transition near room temperature based on nitrogen ligands containing aromatic rings: from molecular design to functional devices

During last decades, significant advances have been made in iron-based spin crossover (SCO) complexes, with a particular emphasis on achieving reversible and reproducible thermal hysteresis at room temperature (RT). This pursuit represents a pivotal goal within the field of molecular magnetism, aiming to create molecular devices capable of operating in ambient conditions. Here, we summarize the recent progress of iron complexes with spin transition near RT based on nitrogen ligands containing aromatic rings from molecular design to functional devices. Specifically, we discuss the various factors, including supramolecular interactions, crystal packing, guest molecules and pressure effects, that could influence its cooperativity and the spin transition temperature. Furthermore, the most recent advances in their implementation as mechanical actuators, switching/memories, sensors, and other devices, have been introduced as well. Finally, we give a perspective on current challenges and future directions in SCO community.

Advancing Molecular-Scale Logic Devices through Multistage Switching in a Luminescent Bimetallic Ru(II)-Terpyridine Complex

Stimuli-responsive multistep switching phenomena of a luminescent bimetallic Ru(II) complex are employed herein to fabricate multiple configurable logic devices. The complex exhibits "off-on" and "on-off" emission switching upon alternative treatment with visible and UV light. Additionally, remarkable augmentation of the rate as well as quantum yield of photoisomerization was achieved via the use of a chemical oxidant (Ce4+) as well as a reductant (metallic sodium). Upon exploiting the emission spectral response of the complex, several advanced Boolean logic functions, including IMPLICATION as well as 2-input 2-output and 3-input 2-output complex combinational logic gates, are successfully implemented. Additionally, by utilizing the vast efficacy of Python, a novel "logic_circuit" model is devised that is capable of making accurate decisions under the influence of various input combinations. This model transcends traditional Boolean logic gates, offering flexibility and intuition to design logical functions tailored to specific chemical contexts. By integrating principles of logic circuits with chemical processes, this innovative approach enables structure determination of the chemical states based on input conditions, thereby unlocking avenues for exploring intricate interactions and reactions beyond conventional Boolean logic paradigms.

Enhancing Control Over Nitric Oxide Photorelease via a Molecular Keypad Lock

Based on Boolean logic, molecular keypad locks secure molecular information, typically with an optical output. Here we investigate a rare example of a molecular keypad lock with a chemical output. To this end, the light-activated release of biologically important nitric oxide from a ruthenium complex is studied, using proton concentration and photon flux as inputs. In a pH-dependent equilibrium, a nitritoruthenium(II) complex is turned into a nitrosylruthenium(II) complex, which releases nitric oxide under irradiation with visible light. The precise prediction of the output nitric oxide concentration as function of the pH and photon flux is achieved with an artificial intelligence approach, namely the adaptive neuro-fuzzy inference system. In this manner an exceptionally high level of control over the output concentration is obtained. Moreover, the provided concept to lock a chemical output as well as the output prediction may be applied to other (photo)release schemes.

Tracing a new path in the field of AI and robotics: mimicking human intelligence through chemistry. Part I: molecular and supramolecular chemistry

Chemical Artificial Intelligence (CAI) is a brand-new research line that exploits molecular, supramolecular, and systems chemistry in wetware (i.e., in fluid solutions) to imitate some performances of human intelligence and promote unconventional robotics based on molecular assemblies, which act in the microscopic world, otherwise tough to be accessed by humans. It is undoubtedly worth spreading the news that AI researchers can rely on the help of chemists and biotechnologists to reach the ambitious goals of building intelligent systems from scratch. This article reports the first attempt at building a Chemical Artificial Intelligence knowledge map and describes the basic intelligent functions that can be implemented through molecular and supramolecular chemistry. Chemical Artificial Intelligence provides new tools and concepts to mimic human intelligence because it shares, with biological intelligence, the same principles and materials. It enables peculiar dynamics, possibly not accessible in software and hardware domains. Moreover, the development of Chemical Artificial Intelligence will contribute to a deeper understanding of the strict link between intelligence and life, which are two of the most remarkable emergent properties shown by the Complex Systems we call biological organisms.

DNA nanopores as artificial membrane channels for bioprotonics

Biological membrane channels mediate information exchange between cells and facilitate molecular recognition. While tuning the shape and function of membrane channels for precision molecular sensing via de-novo routes is complex, an even more significant challenge is interfacing membrane channels with electronic devices for signal readout, which results in low efficiency of information transfer - one of the major barriers to the continued development of high-performance bioelectronic devices. To this end, we integrate membrane spanning DNA nanopores with bioprotonic contacts to create programmable, modular, and efficient artificial ion-channel interfaces. Here we show that cholesterol modified DNA nanopores spontaneously and with remarkable affinity span the lipid bilayer formed over the planar bio-protonic electrode surface and mediate proton transport across the bilayer. Using the ability to easily modify DNA nanostructures, we illustrate that this bioprotonic device can be programmed for electronic recognition of biomolecular signals such as presence of Streptavidin and the cardiac biomarker B-type natriuretic peptide, without modifying the biomolecules. We anticipate this robust interface will allow facile electronic measurement and quantification of biomolecules in a multiplexed manner.

Photo-Induced Fluorochromism of a Star-Shaped Photochromic Dye with 2,4-Dimethylthiazole Attaching to Triangle Terthiophene

A photochrmic triangle terthiophene dye with 2,4-dimethylthiazole attached was synthesized and shows regular photochromic properties when irradiated with UV/Vis light alternately. It was found that the attaching of 2,4-dimethylthiazole has a significant effect on both the photochromism and fluorescence of triangle terthiophene. During the photocyclizatioin prcess, not only the color but also the fluorescence of the dye in THF can be toggled between ring-open and ring-closed forms of the dye. Additionally, the absolute quantum yields (AQY) of ring-open and ring-closed forms of the dye (0.32/0.58) were greatly larger than the literature report. Along with the 254 nm light irradiation, the fluorescence color changed from deep blue (428 nm) to sky blue (486 nm) in THF. A fluorochromism cycle could be established based on the UV/visible light irradiation cycle, which provides a strategy for the design of new type fluorescent diarylethene derivatives for biological application.

Multistate Switching of Some Ruthenium Alkynyl and Vinyl Spiropyran Complexes

To study the switching properties of photochromes, we undertook the synthesis and characterization of several ruthenium organometallic complexes of the type [Ru(Cp*)(dppe)(C≡C-SP)] or [Ru(CO)(dppe)(PPh3)Cl(CH═CH-SP)], where SP = spiropyran. The spectroscopic and electrochemical properties of the complexes were determined by careful cyclic voltammetric and spectroelectrochemical experiments. Whereas the mononuclear alkynyl ruthenium complexes undergo one-electron oxidations localized over the metal alkynyl moiety, the oxidation of the mononuclear vinyl ruthenium complexes is centered on the indoline moiety of the spiropyran. Through these studies, we demonstrate access to several stable redox states, in addition to switching states attained via acidochromism and/or photoisomerization.

Investigating the Properties of Double Triangle Terthiophene Configured Dumbbell-Like Photochromic Dye with Ethyne and 1,3-Butadiene Bridge

Dumbbell-like photochromic dyes were constructed by incorporation of double triangle terthiophene with ethyne or 1,3-butadiene bridge. Regular photochromic behavior was investigated with alternated UV (365 nm) and Visible light (˃ 400 nm) irradiation. However, the different bridge group leads to distinct difference in their photochromic wavelength. For the ethyne bridged triangle terthiophene (DT1), the photochromic wavelength was observed around 500-700 nm (peak value: 605 nm) and the solution turned to red with 365 nm light irradiation. However, the photochromic wavelength was blue shift to 418-550 nm and the solution was turned to light yellow for 1,3-butadiene bridged dye (DT2). Both of the colored solution can be bleached via visible light irradiation. Additionally, the two dyes in THF were emissive with absolute quantum yield (QY) of 0.36/0.40. Along with the photo-induced photocyclization process, the emissive solution can be effectively quenched at photo-stationary sate (Φ = 0.05/0.04). And emission "on-off" cycle could be established based on the UV/visible light irradiation cycle.

Human brain-inspired chemical artificial intelligence tools for the analysis and prediction of the anion-sensing characteristics of an imidazole-based luminescent Os(II)-bipyridine complex

Neural network and decision tree-based soft computing techniques are implemented in this work for the thorough analysis of the multichannel anion-sensing characteristics of an Os(II)-bipyridine complex derived from imidazole-4,5-bis(benzimidazole) ligand. With the aid of three imidazole NH protons in its outer coordination sphere, a substantial change in the spectral response as well as Os^II/Os^III potential is made possible upon treating with anions of varying basicity. Initial hydrogen bonding between NH protons and anions and thereafter complete proton transfer from the complex backbone probably take place in the process. The deprotonation of the complex by specific anions and restoration to its original form by acid is also reversible. The responsiveness of the new compound is complex enough to imitate multiple sophisticated binary and ternary Boolean logic (BL) functions (NOT logic, combinational logic, traffic signal, set-reset flip-flop logic, and ternary NOR logic) by employing its spectral and redox outputs upon the action of suitable anions and acid in a proper sequence. Executing sensing investigations on altering the amount of the anions within a widespread range is often time-consuming and tedious. To overcome the lacuna, we implemented multiple soft computing techniques, viz., fuzzy logic (FL), artificial neural networks (ANNs), adaptive neuro-fuzzy inference system (ANFIS), and decision tree (DT) regression, for the thorough analysis and prediction of the experimentally observed results. The outcomes obtained from different techniques were compared among themselves as well as with the experimental data and utilized for the proper modeling of the anion-sensing behaviors of the complex.

Adaptive 2D and Pseudo-2D Systems: Molecular, Polymeric, and Colloidal Building Blocks for Tailored Complexity

Two-dimensional and pseudo-2D systems come in various forms. Membranes separating protocells from the environment were necessary for life to occur. Later, compartmentalization allowed for the development of more complex cellular structures. Nowadays, 2D materials (e.g., graphene, molybdenum disulfide) are revolutionizing the smart materials industry. Surface engineering allows for novel functionalities, as only a limited number of bulk materials have the desired surface properties. This is realized via physical treatment (e.g., plasma treatment, rubbing), chemical modifications, thin film deposition (using both chemical and physical methods), doping and formulation of composites, or coating. However, artificial systems are usually static. Nature creates dynamic and responsive structures, which facilitates the formation of complex systems. The challenge of nanotechnology, physical chemistry, and materials science is to develop artificial adaptive systems. Dynamic 2D and pseudo-2D designs are needed for future developments of life-like materials and networked chemical systems in which the sequences of the stimuli would control the consecutive stages of the given process. This is crucial to achieving versatility, improved performance, energy efficiency, and sustainability. Here, we review the advancements in studies on adaptive, responsive, dynamic, and out-of-equilibrium 2D and pseudo-2D systems composed of molecules, polymers, and nano/microparticles.

Ratio Fluorescent Detecting of Tryptophan and Its Metabolite 5-Hydroxyindole-3-acetic Acid Relevant with Depression via Tb(III) Modified HOFs Hybrids: Further Designing Recyclable Molecular Logic Gate Connected by Back Propagation Neural Network

Exploring intelligent fluorescent materials with high reliability and precision to diagnose diseases is significant but remains a great challenge. Herein, based on coordination post-synthetic modification, a Tb³⁺ functionalized ME-PA (Tb@1) is prepared, which can emit brilliant green fluorescence through ligand-to-mental charge transfer-assisted energy transfer (LMCT-ET) process from ME-PA to Tb³⁺ ions. Tb@1 can simultaneously distinguish Tryptophan (Try) and its metabolite 5-hydroxyindole-3-acetic acid (5-HIAA), two effective indicators for depression, in ratio and colorimetric mode. And this sensor behaves the advantages of high efficiency and sensitivity, as well as excellent reusability and anti-interference. The PET process from ME to Try and 5-HIAA, and the competitive absorption between analytes and Tb@1 may be relevant to sensing mechanism. In realistic serum or urine environment, the detection limits of Tb@1 for Try and 5-HIAA are 0.0183 and 0.0149 mg L^-1 respectively. Moreover, in conjunction with back propagation neural network (BPNN), two dual-output molecular logic gates that can be calculated circularly are further designed, which realizes intelligent control of the electronic component to identify the existence of two biomarkers and judge their concentrations from fluorescence images. This work offers a novel approach to modulate logic circuits based on ML-assisted HOF fluorescent sensor, with promising application for a precise and pictorial depression diagnosis.

Neural network and decision tree-based machine learning tools to analyse the anion-responsive behaviours of emissive Ru(ii)–terpyridine complexes

Artificial neural network, adaptive neuro-fuzzy inference and decision tree regression are implemented to analyse the anion-responsive behaviours of emissive Ru(ii)–terpyridine complexes.

Investigation of Triangle Terthiophene and Hydroxyphenylbenzothiazole Configured Fluorescent Dye with a Triple Bond Bridge

A photochromic dye was constructed by incorporation of a carbon-carbon triple bond spaced triangle terthiophene skeleton and hydroxyphenylbenzothiazole. Regular photochromic behavior was investigated with alternated UV (254 nm) and visible light (≥ 400 nm) irradiation. The color of dye in solution can be cycled between pink and colorless. Additionally, the dye solution strongly fluoresces in THF with the absolute quantum yield (QY) being 0.56. When irradiation with 254 nm light, the emissive solution can be effectively quenched to photo-stationary sate (Φ = 0.05). An emission "on-off" cycle could be established based on the UV/visible light irradiation cycle. The photochromic dye also exhibits good photo- and thermal-stability at room temperature. The emission decay profile indicates typical single component character with the fluorescence lifetime being 6.68 ns. The emission color was determined by the CIE 1931 coordinates of x = 0.14, y = 0.25 in the blue region.

Three-Input Logic AND Gate Drives Sequential Three-Step Catalysis by Parallel Activation of H+ and Ag+ as a Catalyst Duo

Boolean operations with multiple catalysts as output are yet unknown using molecular logic. The issue is solved using a two-component ensemble, composed of a receptor and rotaxane, which acts as a three-input AND gate with a dual catalytic output. Actuation of the ensemble gate by the stoichiometric addition of metal ions (Ag⁺ and Cd²⁺) and 2,2,2-trifluoroacetic acid generated in the (1,1,1) truth table state a catalyst duo that synergistically enabled a three-step reaction, furnishing a dihydroisoquinoline as the output of a three-input logic AND gate operation.

Analysis and prediction of anion- and temperature responsive behaviours of luminescent Ru(II)-terpyridine complexes by using Boolean, fuzzy logic, artificial neural network and adapted neuro fuzzy inference models

Anion- and temperature responsive behaviors of three luminescent Ru(II)-terpyridine complexes are utilized here to demonstrate multiple Boolean (BL) and fuzzy logic (FL) operations. Taking advantage of the imidazole NH protons, anion-promoted alteration of the photophysical characteristics of the complexes was thoroughly investigated via absorption, and emission spectral and lifetime measurements. In their free state, the complexes display luminescence representing the "on-state", whereas quenching of luminescence is observed with anions demonstrating the "off-state". Likewise, lowering of temperature induces a substantial increase of luminescence and lifetime demonstrating the "on-state", while the increase of temperature induces a significant decrease of emission intensity and lifetime indicating the "off-state" and the process is reversible in both cases. The complexes thus can act as anion- and temperature-responsive molecular switches. The spectral signatures of the complexes under the influence of anions and temperature were employed to mimic multiple BL and FL functions. Performing very detailed sensing studies by varying the analyte concentration within a wide domain is very tedious, time-consuming and expensive. In order to overcome the lacuna, we implemented machine learning and soft computing tools such as artificial neural networks (ANNs), fuzzy-logic and adaptive neuro-fuzzy inference system (ANFIS) to predict the experimental anion sensing data of the complexes.

Catalyst-Based Biomolecular Logic Gates

Regulatory processes in biology can be re-conceptualized in terms of logic gates, analogous to those in computer science. Frequently, biological systems need to respond to multiple, sometimes conflicting, inputs to provide the correct output. The language of logic gates can then be used to model complex signal transduction and metabolic processes. Advances in synthetic biology in turn can be used to construct new logic gates, which find a variety of biotechnology applications including in the production of high value chemicals, biosensing, and drug delivery. In this review, we focus on advances in the construction of logic gates that take advantage of biological catalysts, including both protein-based and nucleic acid-based enzymes. These catalyst-based biomolecular logic gates can read a variety of molecular inputs and provide chemical, optical, and electrical outputs, allowing them to interface with other types of biomolecular logic gates or even extend to inorganic systems. Continued advances in molecular modeling and engineering will facilitate the construction of new logic gates, further expanding the utility of biomolecular computing.

Neuro-Fuzzification Architecture for Modeling of Electrochemical Ion-Sensing Data of Imidazole-Dicarboxylate-Based Ru(II)-Bipyridine Complex

Anion- and pH-sensing behaviors of an imidazole-dicarboxylate-based Ru(II)-bipyridine complex possessing a number of dissociable protons in its secondary coordination sphere are employed here for the creation of multiple Boolean and fuzzy logic systems. The absorption, emission, and electrochemical behaviors of the metalloreceptor were significantly modulated upon the influence of basic anions (such as F^-, AcO^-, and H₂PO₄^-) as well as by altering the pH of the solution. Interestingly, the deprotonation of the metalloreceptor by selected anions or by alkaline pH, followed by its restoration to its original form by acid or acidic pH is reversible and could be repeated many times. The metalloreceptor is capable to demonstrate several advanced Boolean functions, namely, three-input OR gate, set-reset flip-flop logic, and traffic signal, by employing its electrochemical responses through proper use of different inputs. Administering exhaustive sensing experiments by changing the analyte concentration within a wide range is usually tedious as well as exorbitantly costly. To get rid of these difficulties, we employed here several soft computing approaches such as artificial neural networks (ANN), fuzzy logic systems (FLS), or adaptive neuro-fuzzy inference system (ANFIS) to foresee the experimental sensing data and to appropriately model the protonation-deprotonation behaviors of the metalloreceptor. Reasonably good correlation between the experimental and model output data is also reflected in their tested root-mean-square error values (0.115961 and 0.118894 for the ANFIS model).

Aggregation induced emission based fluorenes as dual-channel fluorescent probes for rapid detection of cyanide: applications of smartphones and logic gates

Rational modification of molecular structure by incorporating electron donating groups can play a potential role for designing aggregation induced emission (AIE) active fluorescent probes. Based on this principle, fluorescent probes (1a–c) were synthesized, and they displayed excellent aggregation induced emission (AIE) behavior in a H₂O/DMF (4 : 1, v/v) mixture due to restrictions in intramolecular charge transfer (ICT). As a comparison, probe 1d was synthesized by installing an electron withdrawing (–NO₂) group that surprisingly quenched the aggregation behaviour. Additionally, AIE active probes 1a–c displayed a highly sensitive dual channel (fluorometric and colorimetric) response towards rapid detection of CN⁻, which is an active toxic material. Probes 1a–c showed selectively enhanced fluorescence emission behavior towards CN⁻ with detection limits of 1.34 ppb, 1.38 ppb, and 1.54 ppb, respectively. The sensing mechanism involves Michael type adduct formation due to the nucleophilic addition reaction of cyanide with probes and was confirmed through ¹H NMR titration experiments. In contrast, probe 1d containing an electron withdrawing moiety showed insensitivity towards CN⁻. Therefore, this study provides the efficient strategy to induce AIE character in fluorescent probes and expands the mechanistic approach toward the sensing of toxic CN⁻.

Rational modification of molecular structure by incorporating electron donating groups can play a potential role for designing aggregation induced emission (AIE) active fluorescent probes.

Small-scale soft grippers with environmentally responsive logic gates

Small-scale soft grippers are adaptive and deformable, and can be utilized for confined environments (e.g., the human body). Small-scale soft grippers require logic-based computation to achieve intelligent control and perform logical analysis of the surrounding information. However, it is a great challenge to integrate electronic chips and power supplies (i.e., batteries) on their small systems. Here, the approach provides a route to add computational capabilities via environmentally responsive logic gates in small-scale soft grippers, without electronics, external control, or tethering. Various origami-inspired grippers performing YES, NOT, XOR, AND, OR, NOR and NAND gates, respectively, were developed by stimuli-responsive hydrogels as building blocks. Although the hydrogels respond to different kinds of stimuli, their outputs are the same: a change in hydrogel size, leading to the bending of the arms of the grippers. Hence, the logic gates can be integrated easily within a gripper (e.g., connecting an AND gate to another AND gate). Moreover, the gripper fabricated by dual-responsive hydrogels can intelligently and autonomously switch from an AND gate to an OR gate upon varied environmental stimuli. In addition, a magnetic gripper with an AND gate was fabricated that can analyse different stimuli, and capture and release the targeted object via the environmentally responsive logic gates. This strategy provides a new route to incorporate on-board perception, control and computation via environmentally responsive logic gates in small-scale soft robots and machines.

A rhodamine based dual chemosensor for Al3+ and Hg2+: Application in the construction of advanced logic gates

A rhodamine-based compound (RBO), which has been constructed from the reaction between N-(rhodamine-6G)lactam-ethylenediamine and 2,1,3-benzoxadiazole-4-carbaldehyde, is reported here as a selective chemosensor for both Al³⁺ and Hg²⁺ ions in 10 mM HEPES buffer in water:ethanol (1:9, pH = 7.4). Absorption intensity of RBO increases considerably at 528 nm with these cations. It shows fluorescence enhancement at 550 nm by 1140- and 524-fold in the presence of Al³⁺ and Hg²⁺, respectively. LOD has been determined as 6.54 and 16.0 nM for Al³⁺ and Hg²⁺, respectively. Quantum yield and lifetime of RBO enhances with these metal ions. Fluorescence intensity of Al-probe complex or Hg-probe complex is quenched in the presence of fluoride or sulfide ion, respectively, opening a path for the construction logic gates. DFT analysis has been used to understand the spectral transitions. We have constructed a systematic development from single to five inputs complex circuit, and for the first time a time dependent five input complex logic circuit is reported herein.

Dual-Site Fluorescent Sensor as a Multiple Logic System for Studying the Dichotomous Function of Sulfur Dioxide under Oxidative Stress Induced by Peroxynitrite

Intracellular reactive oxygen species and reactive sulfur play a vital role in regulating redox homeostasis and maintaining cell functions. Sulfur dioxide (SO₂) has emerged as an important gas signal molecule recently, which is not only a potential reducing agent but also a potential inductor of oxidative stress in organisms. Due to high reactivity, peroxynitrite (ONOO^-) could act on many biomolecules, such as proteins, lipids, and nucleic acids, and cause irreversible damage, eventually leading to cell apoptosis or necrosis. In order to further illuminate the dichotomous role of SO₂ under oxidative stress induced by ONOO^-, we designed the first dual-site fluorescent sensor (NIR-GYf) for separate or continuous detection of SO₂ and ONOO^-. NIR-GYf was successfully used for cell imaging of endogenous SO₂ and ONOO^-. In addition, western blotting analysis was used to verify the oxidation and antioxidation of SO₂ and its dichotomous biological influence. Finally, NIR-GYf was integrated with multiple Boolean logic operations to construct an advanced analysis device, thereby realizing the direct analysis of SO₂ and ONOO^- levels.

β-Cyclodextrin Supramolecular Recognition of bis-Cationic Dithienylethenes

The supramolecular interactions in water between β-cyclodextrin and the open and closed photochromic forms of two bis-cationic dithienylethenes, characterized by different electronic properties, were investigated aiming at underlying the key aspects of the recognition process. The dithienylethene equipped with the cyclopentenyl unit showed a difference in binding free energies to the β-cyclodextrin between the open and closed photochromic forms of about 1 kJ/mol. Conversely, the dithienylethene equipped with the perfluorinated cyclopentenyl unit not only was a better guest but showed a three times higher difference in the binding of free energies between the open and closed isomers.

A DNA-Based Two-Component Excitonic Switch Utilizing High-Performance Diarylethenes

Nucleosidic diarylethenes (DAEs) are an emerging class of photochromes but have rarely been used in materials science. Here, we have developed doubly methylated DAEs derived from 2'-deoxyuridine with high thermal stability and fatigue resistance. These new photoswitches not only outperform their predecessors but also rival classical non-nucleosidic DAEs. To demonstrate the utility of these new DAEs, we have designed an all-optical excitonic switch consisting of two oligonucleotides: one strand containing a fluorogenic double-methylated 2'-deoxyuridine as a fluorescence donor and the other a tricyclic cytidine (tC) as acceptor, which together form a highly efficient conditional Förster-Resonance-Energy-Transfer (FRET) pair. The system was operated in liquid and solid phases and showed both strong distance- and orientation-dependent photochromic FRET. The superior ON/OFF contrast was maintained over up to 100 switching cycles, with no detectable fatigue.

Emissive and reactive excimers in a covalently-linked supramolecular multi-chromophoric system with a balanced rigid-flexible structure

A novel multi-chromophoric system, triad, in which two styrylbenzoquinoline (SBQ) photochromes are connected by a balanced rigid-flexible linker comprising 2,3-naphthylene framework (a residue of 3-oxy-2-naphthoic acid) and tetramethylene groups, was designed and synthesized to study an excimer formation in the excited state. The ¹H NMR data testified that triad exists in solution as folded conformers with asymmetric parallel-displaced SBQ units. Under light irradiation, in the triad, competitive photoisomerization and [2 + 2] photocycloaddition reactions were observed, both reactions being reversible. The photocycloaddition resulted in a tetrasubstituted cyclobutane. The red-shifted fluorescence spectrum and the appearance of a long-lived component in the triad fluorescence decay indicated formation of an 'emissive' excimer. The photocycloaddition is assumed to occur in a 'reactive' excimer, in which the ethylene groups of the SBQ photochromes are located at a distance sufficient for the formation of the σ-bonds between them. Quantum-chemical density functional theory (DFT) calculations at M06-2X/6-31G* level predicted the existence of the triad conformers with π-stacking interaction of SBQ photochromes, the structure of which is pre-organized for the excimer formation and photocycloaddition. For the first time, both emissive and reactive excimers were experimentally observed in the multi-chromophoric system with two diarylethylene photochromes undergoing [2 + 2] photocycloaddition.

Anion and Temperature Responsive Molecular Switches Based on Trimetallic Complexes of Ru(II) and Os(II) That Demonstrate Advanced Boolean and Fuzzy Logic Functions

Anion- and temperature-induced alteration of the photoredox behaviors of our recently reported trimetallic complexes was carried out to fabricate potential molecular switches. The triads [(phen)₂Ru(d-HIm-t)M(t-HIm-d)Ru(phen)₂]⁶⁺ (phen = 1,10-phenanthroline, d-HIm-t = heterotopic bipyridine-terpyridne type bridging ligand, and M = Ru^II and Os^II) possess two acidic imidazole NH protons that upon interaction with anions give rise to considerable changes in their photophysical and electrochemical behaviors. Red-shifts of the absorption and emission maximum and a decrease in the M³⁺/M²⁺ potential occur when the triads are treated with basic anions. In fact, the triads can function as triple-channel sensors for F^-, AcO^-, CN^-, OH^-, and H₂PO₄^- in acetonitrile and as selective probes for CN^- and SCN^- in water. The equilibrium constants for the receptor-anion interaction are on the order of 10⁶ M^-1, while the limit of detection was on the order of 10^-9 M. Temperature plays a key role in the luminescence properties of the triads by adjusting the energy barrier between the emitting triplet metal-to-ligand charge transfer and non-emitting triplet metal-centered levels. A decrease in temperature leads to increases in the emission intensity and lifetime of the triads displaying the "on state", whereas an increase in temperature leads to a decrease in their emission characteristics and thus indicates the "off state" and that the process is fully reversible. In essence, the triads could function as potential switches on the basis of the reversible change in their spectral and redox behaviors under the influence of anion, acid, and temperature. The most important outcome of this study is mimicking several advanced Boolean and fuzzy logic functions by utilizing the spectral response of the triads upon the action of said external stimuli.

A gama-turn mimetic for selective sensing of Cu(II) and combinatorial multiple logic gate

We have designed and synthesized a gama-turn mimetic using fenamic acid and α-aminoisobutyricacid (Aib), the conformation and optoelectronic properties of which can be changed by appropriate external stimuli. From single-crystal...

Molecular engineering of fluorescent bichromophore 1,3,5-triaryl-Δ2-pyrazoline and 4-amino-1,8-naphthalimide molecular logic gates

Emissive bichromophoric solvatochromatic molecules are introduced as a new platform for the development of fluorescent molecular logic gates.

Synthesis of an advanced metal-guided photochromic system for molecular keypad lock: detailed experimental findings and theoretical understanding

The dye-containing Schiff base metal complex is a new member of the photochromic family with advantages, such as long-wavelength absorption, high molar absorption coefficient, quick-photoresponse, and excellent fatigue resistance.

Exciton Delocalization and Scaffold Stability in Bridged Nucleotide-Substituted, DNA Duplex-Templated Cyanine Aggregates

Molecular excitons play a foundational role in chromophore aggregates found in light-harvesting systems and offer potential applications in engineered excitonic systems. Controlled aggregation of chromophores to promote exciton delocalization has been achieved by covalently tethering chromophores to deoxyribonucleic acid (DNA) scaffolds. Although many studies have documented changes in the optical properties of chromophores upon aggregation using DNA scaffolds, more limited work has investigated how structural modifications of DNA via bridged nucleotides and chromophore covalent attachment impact scaffold stability as well as the configuration and optical behavior of attached aggregates. Here we investigated the impact of two types of bridged nucleotides, LNA and BNA, as a structural modification of duplex DNA-templated cyanine (Cy5) aggregates. The bridged nucleotides were incorporated in the domain of one to four Cy5 chromophores attached between adjacent bases of a DNA duplex. We found that bridged nucleotides increase the stability of DNA scaffolds carrying Cy5 aggregates in comparison with natural nucleotides in analogous constructs. Exciton coupling strength and delocalization in Cy5 aggregates were evaluated via steady-state absorption, circular dichroism, and theoretical modeling. Replacing natural nucleotides with bridged nucleotides resulted in a noticeable increase in the coupling strength (≥10 meV) between chromophores and increased H-like stacking behavior (i.e., more face-to-face stacking). Our results suggest that bridged nucleotides may be useful for increasing scaffold stability and coupling between DNA templated chromophores.

Thermal and photoinduced spin-crossover of mononuclear FeII complexes based on bppCHO ligand

Two new iron(II) complexes [Fe(bppCHO)₂](ClO₄)₂ (1·ClO4) and [Fe(bppCHO)₂](BF₄)₂·H₂O (1·BF4) were synthesized by using 2,6-di(1H-pyrazol-1-yl)isonicotinaldehyde (bppCHO) as the ligand. The structures and spin states of the complexes were characterized by single-crystal X-ray diffraction and magnetic susceptibility measurements. Complex 1·ClO4 exhibits light-induced excited spin state trapping (LIESST) up to 53 K and two-step spin-crossover (SCO) over room temperature, in which the first step shows a thermal hysteresis of 26 K, whereas 1·BF4 exhibits a gradual SCO behavior. A magnetostructural study reveals that the difference in the SCO property is related to the supramolecular interactions and crystal packing effect.

Molecular Approach to Engineer Two-Dimensional Devices for CMOS and beyond-CMOS Applications

Two-dimensional materials (2DMs) have attracted tremendous research interest over the last two decades. Their unique optical, electronic, thermal, and mechanical properties make 2DMs key building blocks for the fabrication of novel complementary metal-oxide-semiconductor (CMOS) and beyond-CMOS devices. Major advances in device functionality and performance have been made by the covalent or noncovalent functionalization of 2DMs with molecules: while the molecular coating of metal electrodes and dielectrics allows for more efficient charge injection and transport through the 2DMs, the combination of dynamic molecular systems, capable to respond to external stimuli, with 2DMs makes it possible to generate hybrid systems possessing new properties by realizing stimuli-responsive functional devices and thereby enabling functional diversification in More-than-Moore technologies. In this review, we first introduce emerging 2DMs, various classes of (macro)molecules, and molecular switches and discuss their relevant properties. We then turn to 2DM/molecule hybrid systems and the various physical and chemical strategies used to synthesize them. Next, we discuss the use of molecules and assemblies thereof to boost the performance of 2D transistors for CMOS applications and to impart diverse functionalities in beyond-CMOS devices. Finally, we present the challenges, opportunities, and long-term perspectives in this technologically promising field.

Design and engineering of a dual-mode absorption/emission molecular switch for all-optical encryption

Photochemical reactions that produce a detectable change in the spectroscopic properties of organic chromophores can be exploited to harness the principles of Boolean algebra and design molecule-based logic circuits. Moreover, the logic processing capabilities of these photoactive molecules can be directed to protect, encode, and conceal information at the molecular level. We have designed a photochemical strategy to read, write and encrypt data in the form of optical signals. We have synthesized a supramolecular system based on the known dye resazurin, and investigated a series of photochemical transformations that can be used to regulate its absorption and emission properties upon illumination with ultraviolet or visible light. We have then examined the logic behaviour of the photochemistry involved, and illustrated its potential application in data encryption.

Fluorescent Molecular Logic Gates Driven by Temperature and by Protons in Solution and on Solid

Temperature-driven fluorescent NOT logic is demonstrated by exploiting predissociation in a 1,3,5-trisubstituted Δ² -pyrazoline on its own and when grafted onto silica microparticles. Related Δ² -pyrazolines become proton-driven YES and NOT logic gates on the basis of fluorescent photoinduced electron transfer (PET) switches. Additional PASS 1 and YES+PASS 1 logic gates on silica are also demonstrated within the same family. Beside these small-molecule systems, a polymeric molecular thermometer based on a benzofurazan-derivatized N-isopropylacrylamide copolymer is attached to silica to produce temperature-driven fluorescent YES logic.