Light-stimulated molecular and supramolecular systems for information processing and beyond

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.

"On-the-Fly" Nonadiabatic Dynamics Simulation on the Ultrafast Photoisomerization of a Molecular Photoswitch Iminothioindoxyl: An RMS-CASPT2 Investigation

Iminothioindoxyl (ITI) is a new class of photoswitch that exhibits many excellent properties including well-separated absorption bands in the visible region for both conformers, ultrafast Z to E photoisomerization as well as the millisecond reisomerization at room temperature for the E isomer, and switchable ability in both solids and various solvents. However, the underlying ultrafast photoisomerization mechanism at the atomic level remains unclear. In this work, we have employed a combination of high-level RMS-CASPT2-based static electronic structure calculations and nonadiabatic dynamics simulations to investigate the ultrafast photoisomerization dynamics of ITI. Based on the minimum-energy structures, minimum-energy conical intersections, linear interpolation internal coordinate paths, and nonadiabatic dynamics simulations, the overall photoisomerization scenario of ITI upon excitation is established. Upon excitation around 416 nm, the molecule will be excited to the S2 state considering its close energy to the experimentally measured absorption maximum and larger oscillator strength, from which ultrafast decay of S2 to S1 state can take place efficiently with a time constant of 62 fs. However, the photoisomerization is not likely to complete in the S2 state since the dihedral associated with the Z to E isomerization changes little during the relaxation. Upon relaxing to the S1 state, the molecule will decay to the S0 state ultrafast with a time constant of 232 fs. In contrast, the decay of the S1 state is important for the isomerization considering that the dihedral related to the isomerization of the hopping structures is close to 90°. Therefore, the S1/S0 intersection region should be important for the isomerization of ITI. Arriving at the S0 state, the molecule can either go back to the original Z reactant or isomerize to the E products. At the end of the 500 fs simulation time, the E configuration accounts for nearly 37% of the final structures. Moreover, the photoisomerization mechanism is different from the isomerization mechanism in the ground state; i.e., instead of the inversion mechanism in the ground state, the photoisomerization prefers the rotation mechanism. Our results not only agree well with previous experimental studies but also provide some novel insights that could be helpful for future improvements in the performance of the ITI photoswitches.

Light-triggered transformation of stilbene supramolecular polymers: thermodynamic versus kinetic control

Light irradiation of stilbene supramolecular polymers produces [2+2] cycloadducts in the kinetically trapped state, which convert to the thermodynamically favorable state upon thermal annealing due to the shift of hydrogen bonds from intra- to inter-complexation modes.

Robust Red-Absorbing Donor-Acceptor Stenhouse Adduct Photoswitches

Donor-Acceptor Stenhouse Adduct (DASA), a class of push-pull negative photochrome, has received large interest lately owing to its versatile synthesis, modularity and excellent photoswitching in solutions. From a technological perspective, it is imperative for this class of photoswitches to work robustly in solid state, e. g. thin films. We feature a molecular framework for the optimized design of DASAs by introducing a new thioindoline donor (D3) and assessing its performance against known 2nd generation indoline-based donors. The systematic structure-function investigations suggest that to achieve robust reversible photoswitching, a ground state with low charge separation is desired. DASAs with stronger electron donors and a larger charge separation in the ground state result in a low population of the photothermalstationary state (PTSS) and reduced photostability. The DASA with thioindoline donor (D3A3) seems to be a special case among the donor series as it causes a red shift (ca. 15 nm), however with less polarization of the ground state and marginally better photostability as compared to the unsubstituted 2-methyl indoline (D1A3). We also emphasize the consideration of the key additional factors that can modulate the red-light photoswitching properties of DASA chromophores in polymer thin films, which might not be dominant in homogenous solution state.

Photoswitching the fluorescence of nanoparticles for advanced optical applications

The dynamic optical response properties and the distinct features of nanomaterials make photoswitchable fluorescent nanoparticles (PF NPs) attractive candidates for advanced optical applications. Over the past few decades, the design of PF NPs by coupling photochromic and fluorescent motifs at the nanoscale has been actively pursued, and substantial efforts have been made to exploit their potential applications. In this perspective, we critically summarize various design principles for fabricating these PF NPs. Then, we discuss their distinct optical properties from different aspects by highlighting the capability of NPs in fabricating new, robust photoswitch systems. Afterwards, we introduce the pivotal role of PF NPs in advanced optical applications, including sensing, anti-counterfeiting and imaging. Finally, current challenges and future development of PF NPs are briefly discussed.

Control of Photoisomerization Kinetics via Multistage Switching in Bimetallic Ru(II)-Terpyridine Complexes

In this study, we carried out detailed experimental and theoretical investigation on photophysical, electrochemical, and photoisomerization behaviors of a new array of luminescent binuclear Ru(II) complexes derived from a phenylene-vinylene-substituted terpyridyl ligand possessing RT lifetimes within 60.3-410.5 ns. The complexes experienced trans-to-cis isomerization in MeCN on irradiation with visible light, accompanied by significant changes in their absorption and emission spectral profiles. The reverse cis-to-trans process is also possible with the use of ultraviolet (UV) light. On conversion from trans to cis isomers, the emission intensity increases substantially, while for the reverse process, luminescence quenching occurs. Thus, "off-on" and "on-off" emission switching is facilitated upon treatment with visible and UV light alternatively. By the use of chemical oxidants (ceric ammonium nitrate and potassium permanganate) and reductants (metallic sodium) as well as light of appropriate wavelengths, multistate switching phenomena involving reversible oxidation-reduction and trans-cis isomerization have been achieved. Interestingly, the rate of this multistate photoswitching process becomes much faster compared to only two-state trans-cis isomerization of these complexes. Density functional theory (DFT) and time-dependent-DFT (TD-DFT) calculations are also performed to obtain a clear picture of the electronic environment of the complexes and also for the appropriate assignment of absorption and emission spectral bands.

Synthesis of photo- and ionochromic N-acylated 2-(aminomethylene)benzo[b]thiophene-3(2Н)-ones with a terminal phenanthroline group

A series of novel photo- and ionochromic N-acylated 2-(aminomethylene)benzo[b]thiophene-3(2Н)-ones with a terminal phenanthroline receptor substituent was synthesized. Upon irradiation in acetonitrile or DMSO with light of 436 nm, they underwent Z-E isomerization of the C=C bond, followed by very fast N→O migration of the acyl group and the formation of nonemissive O-acylated isomers. These isomers were isolated preparatively and fully characterized by IR, 1H, and 13C NMR spectroscopy as well as HRMS and XRD methods. The reverse thermal reaction was catalyzed by protonic acids. N-Acylated compounds exclusively with Fe2+ formed nonfluorescent complexes with a contrast naked-eye effect: a color change of the solutions from yellow to dark orange. Subsequent selective interaction with AcO- led to the restoration of the initial absorption and emission properties. Thus, the obtained compounds represent dual-mode "on-off-on" switches of optical and fluorescent properties under sequential exposure to light and H+ or sequential addition of Fe2+ and AcO- ions.

A framework for multiexcitonic logic

Exciton science sits at the intersection of chemical, optical and spin-based implementations of information processing, but using excitons to conduct logical operations remains relatively unexplored. Excitons encoding information could be read optically (photoexcitation-photoemission) or electrically (charge recombination-separation), travel through materials via exciton energy transfer, and interact with one another in stimuli-responsive molecular excitonic devices. Excitonic logic offers the potential to mediate electrical, optical and chemical information. Additionally, high-spin triplet and quintet (multi)excitons offer access to well defined spin states of relevance to magnetic field effects, classical spintronics and spin-based quantum information science. In this Roadmap, we propose a framework for developing excitonic computing based on singlet fission (SF) and triplet-triplet annihilation (TTA). Various molecular components capable of modulating SF/TTA for logical operations are suggested, including molecular photo-switching and multi-colour photoexcitation. We then outline a pathway for constructing excitonic logic devices, considering aspects of circuit assembly, logical operation synchronization, and exciton transport and amplification. Promising future directions and challenges are identified, and the potential for realizing excitonic computing in the near future is discussed.

Orthogonal Initiation of Molecular Motion Devices by Two Chemical Fuels

Herein, we demonstrate the selective dissipative and orthogonal actuation of two distinct molecular devices controlled by alternate fuel use. When the multicomponent ensemble of [2]rotaxane 1 and turnstile [Cu(2)(3)]+ was charged with AgBF4 as chemical fuel (Fuel 1) together with NEt3/PhCH2Br (cofuels), the transiently formed [Ag(1)]+ showed a stochastic shuttling of the silver macrocycle between two degenerate triazole stations on the thread (k298 = 1.2 × 105 s-1), whereas [Cu(2)(3)]+ was unperturbed. Instead, treatment of the mixture with PPh3 as an alternative fuel (Fuel 2) in the presence of oxidant 4 (cofuel) generated the complex [Cu(3)(PPh3)2]+ and transient thermal motion in rotor 2 (k298 = 4.9 × 104 s-1), whereas rotaxane 1 stayed dormant. Thus, two distinct chemical fuels selectively and orthogonally activated two distinct transient motion devices from a multicomponent mixture. In total, four interference-free dissipative cycles were demonstrated by using alternating fuel additions.

Conducting 1D nanostructures from light-stimulated copper-metalated porphyrin-dibenzothiophene

Control over the dimensionality of stimulated organic semiconductors has aroused significant interest in organic electronics; however, the design of such materials still remains to be decided. Herein, we have developed three dibenzothiophene-appended freebase, zinc-metalated and copper-metalated porphyrin derivatives (PFb-DBT, PZn-DBT and PCu-DBT) in which PCu-DBT leads to an anion-binding complex in chloroform upon the application of light, resulting in self-assembled 1D nanostructures with high electrical conductivity. Nevertheless, light-stimulated freebase and zinc-metalated P-DBT undergo protonation and demetalation. Electron microscopic images displayed the anion-binding-assisted 1D nanostructure using weak non-covalent interactions, which promotes enhancement in electrical conductivity among other things, as confirmed by electrochemical impedance spectra. Thus, the generation of well-defined nanostructures with improved electronic characteristics from stimuli-responsive organic dyes suggests the importance of developing various smart materials for efficient field effect transistors and sensors.

Quantifying the Relaxation Dynamics of Higher Electronic Excited States in Perylene

Gating logical operations through high-lying electronic excited states presents opportunities for developing ultrafast, subnanometer computational devices. A lack of molecular systems with sufficiently long-lived higher excited states has hindered practical realization of such devices, but recent studies have reported intriguing photophysics from high-lying excited states of perylene. In this work, we use femtosecond spectroscopy supported by quantum chemical calculations to identify and quantify the relaxation dynamics of monomeric perylene's higher electronic excited states. The 21B2u state is accessed through single-photon absorption at 250 nm, while the optically dark 21Ag state is excited via the 11B3u state. Population of either state results in subpicosecond relaxation to the 11B3u state, and we quantify 21Ag and 21B2u state lifetimes of 340 and 530 fs, respectively. These lifetimes are significantly longer than the singlet fission time constant from the perylene 21B2u state, suggesting that the higher electronic states of perylene may be useful for gating logical operations.

A Tutorial Review on the Fluorescent Probes as a Molecular Logic Circuit-Digital Comparator

The rapid progress in the field of fluorescent probes and fluorescent sensing material extended this research area toward more complex molecular logic gates capable of carrying out a variety of sensing functions simultaneously. These molecules are able to calculate a composite result in which the analysis is not performed by a man but by the molecular device itself. Since the first report by de Silva of AND molecular logic gate, all possible logic gates have been achieved at the molecular level, and currently, utilization of more complicated molecular logic circuits is a major task in this field. Comparison between two digits is the simplest logic operation, which could be realized with the simplest logic circuit. That is why the right understanding of the applied principles during the implementation of molecular digital comparators could play a critical role in obtaining logic circuits that are more complicated. Herein, all possible ways for the construction of comparators on the molecular level were discussed, and recent achievements connected with these devices were presented.

Proton-Coupled Photochromic Hemithioindigo: Toward Photoactivated Chemical Sensing and Imaging

We report photoswitchable fluorescent hemithioindigos (HTIs) where the metastable E isomers were stabilized by the proton-bridged intramolecular hydrogen bond. Titration experiments and computational analysis indicated that the E isomers were much more basic than the Z isomers, which enabled photoactivated colorimetric and fluorescent pH response in solvents and polypropylene films. The HTIs exhibited reversibly switchable fluorescence with the Z isomers being the most fluorescent. Moreover, the HTIs were lysosomotropic and the kinetic fluorescence evolution during photoswitching was able to differentiate subcellular compartments with different pH. The combination of photoenhanced basicity, switchable fluorescence, and proton-coupled photochromism lay the groundwork for a broad range of chemical and biological applications.

Proton transfer network with luminescence display controls OFF/ON catalysis that generates a high-speed slider-on-deck

A three-component network for OFF/ON catalysis was built from a protonated nanoswitch and a luminophore. Its activation by addition of silver(i) triggered the proton-catalyzed formation of a biped and the assembly of a fast slider-on-deck (k 298 = 540 kHz).

Metal-Photoswitch Friendship: From Photochromic Complexes to Functional Materials

Cooperative metal-photoswitch interfaces comprise an application-driven field which is based on strategic coupling of metal cations and organic photochromic molecules to advance the behavior of both components, resulting in dynamic molecular and material properties controlled through external stimuli. In this Perspective, we highlight the ways in which metal-photoswitch interplay can be utilized as a tool to modulate a system's physicochemical properties and performance in a variety of structural motifs, including discrete molecular complexes or cages, as well as periodic structures such as metal-organic frameworks. This Perspective starts with photochromic molecular complexes as the smallest subunit in which metal-photoswitch interactions can occur, and progresses toward functional materials. In particular, we explore the role of the metal-photoswitch relationship for gaining fundamental knowledge of switchable electronic and magnetic properties, as well as in the design of stimuli-responsive sensors, optically gated memory devices, catalysts, and photodynamic therapeutic agents. The abundance of stimuli-responsive systems in the natural world only foreshadows the creative directions that will uncover the full potential of metal-photoswitch interactions in the coming years.

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.

Enhanced Sampling Aided Design of Molecular Photoswitches

Advances in the evolving field of atomistic simulations promise important insights for the design and fundamental understanding of novel molecular photoswitches. Here, we use state-of-the-art enhanced simulation techniques to unravel the complex, multistep chemistry of donor-acceptor Stenhouse adducts (DASAs). Our reaction discovery workflow consists of enhanced sampling for efficient chemical space exploration, refinement of newly observed pathways with more accurate ab initio electronic structure calculations, and structural modifications to introduce design principles within future generations of DASAs. We showcase our discovery workflow by not only recovering the full photoswitching mechanism of DASA but also predicting a plethora of new plausible thermal pathways and suggesting a way for their experimental validation. Furthermore, we illustrate the tunability of these newly discovered reactions, leading to a potential avenue for controlling DASA dynamics through multiple external stimuli. Overall, these insights could offer alternative routes to increase the efficiency and control of DASA's photoswitching mechanism, providing new elements to design more complex light-responsive materials.

Multiple molecular logic gate arrays in one system of (2-(2'-pyridyl)imidazole)Ru(ii) complexes and trimeric cyclophanes in water

Shape-switchable cyclophane hosts allow the controlled capture and release of reactive polypyridineRu(ii) complexes in water. This gives rise to a network of host-guest binding, acid-base reactions in ground and excited states, and chemical redox interconversions. In the case of (2-(2'-pyridyl)imidazole)Ru(ii) complexes, several molecular logic gate arrays of varying complexity emerge as a result. Cyclophane-induced 'off-on' switching of luminescence in neutral solution is found to originate from two features of these aromatic hosts: enhancement of radiative decay by the polarizable host and the suppression of nonradiative decay involving deprotonation by reducing the water content within the deep host cavity. These are examples of nanometric coordination chemistry/physics being controlled by inclusion in an open box. The aromatic units of the macrocycle are also responsible for the shape-switching mechanism of wall collapse/erection.

A photoinduced mixed valence photoswitch

The ground state and photoinduced mixed valence states (GSMV and PIMV, respectively) of a dinuclear (Dp⁴⁺) ruthenium(II) complex bearing 2,2'-bipyridine ancillary ligands and a 2,2':4',4'':2'',2'''-quaterpyridine (Lp) bridging ligand were investigated using femtosecond and nanosecond transient absorption spectroscopy, electrochemistry and density functional theory. It was shown that the electronic coupling between the transiently light-generated Ru(II) and Ru(III) centers is H_DA ∼ 450 cm^-1 in the PIMV state, whereas the electrochemically generated GSMV state showed H_DA ∼ 0 cm^-1, despite virtually identical Ru-Ru distances. This stemmed from the changes in dihedral angles between the two bpy moieties of Lp, estimated at 30° and 4° for the GSMV and PIMV states, respectively, consistent with a through-bond rather than a through-space mechanism. Electronic coupling can be turned on by using visible light excitation, making Dp⁴⁺ a competitive candidate for photoswitching applications. A novel strategy to design photoinduced charge transfer molecular switches is proposed.

A multi-stage single photochrome system for controlled photoswitching responses

The ability of molecular photoswitches to convert on/off responses into large macroscale property change is fundamental to light-responsive materials. However, moving beyond simple binary responses necessitates the introduction of new elements that control the chemistry of the photoswitching process at the molecular scale. To achieve this goal, we designed, synthesized and developed a single photochrome, based on a modified donor-acceptor Stenhouse adduct (DASA), capable of independently addressing multiple molecular states. The multi-stage photoswitch enables complex switching phenomena. To demonstrate this, we show spatial control of the transformation of a three-stage photoswitch by tuning the population of intermediates along the multi-step reaction pathway of the DASAs without interfering with either the first or final stage. This allows for a photonic three-stage logic gate where the secondary wavelength solely negates the input of the primary wavelength. These results provide a new strategy to move beyond traditional on/off binary photochromic systems and enable the design of future molecular logic systems.

Heteroleptic metallosupramolecular aggregates/complexation for supramolecular catalysis

Supramolecular catalysis is reviewed with an eye on heteroleptic aggregates/complexation. Since most of the current metallosupramolecular catalytic systems are homoleptic in nature, the idea of breaking/reducing symmetry has ignited a vivid search for heteroleptic aggregates that are made up by different components. Their higher degree of functional diversity and structural heterogeneity allows, as demonstrated by Nature by the multicomponent ATP synthase motor, a more detailed and refined configuration of purposeful machinery. Furthermore, (metallo)supramolecular catalysis is shown to extend beyond the single "supramolecular unit" and to reach far into the field and concepts of systems chemistry and information science.

Recent advances in dual-target-activated fluorescent probes for biosensing and bioimaging

Fluorescent probes have been powerful tools for visualizing and quantifying multiple dynamic processes in living cells. However, the currently developed probes are often constructed by conjugation a fluorophore with a recognition moiety and given signal-output after triggering with one singly target interest. Compared with the single-target-activated fluorescent probes mentioned above, the dual-target-activated ones, triggering with one target under stimulus (such as photoirradiation, microenvironment) or another targets, have the advantages of advoiding nonspecific activation and "false positive" results in complicated environments. In recent years, many dual-target-activated fluorescent probes have been developed to detect various biologically relevant species. In view of the importance of a comprehensive understanding of dual-target- activated fluorescent probes, a thorough summary of this topic is urgently needed. However, no comprehensive and critical review on dual target activated fluorescent probes has been published recently. In this review, we focus on the dual-target-activated fluorescent probes and briefly outline their types and current state of development. In each type, the chemical structure, proposed responsive mechanism and application of probes are highlighted. At last, the challenges and prospective opportunities of every type were proposed.

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.

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.

“The red cage”: implementation of pH-responsiveness within a macrobicyclic pyridinium-based molecular host

The “red cage”, a new pyridinium-based macrobicyclic host, has been found to complex model aromatic substrates in aqueous media in a pH-responsive fashion.

Large, Tunable, and Reversible pH Changes by Merocyanine Photoacids

Molecular photoswitches capable of generating precise pH changes will allow pH-dependent processes to be controlled remotely and noninvasively with light. We introduce a series of new merocyanine photoswitches, which deliver reversible bulk pH changes up to 3.2 pH units (pH 6.5 to pH 3.3) upon irradiation with 450 nm light, displaying tunable and predictable timescales for thermal recovery. We present models to show that the key parameters for optimizing the bulk pH changes are measurable: the solubility of the photoswitch, the acidity of the merocyanine form, the thermal equilibrium position between the spiropyran and the merocyanine isomers, and the increased acidity under visible light irradiation. Using ultrafast transient absorption spectroscopy, we determined the quantum yields for the ring-closing reaction and found that the lifetimes of the transient cis-merocyanine isomers ranged from 30 to 550 ns. Quantum yields did not appear to be a limitation for bulk pH switching. The models we present use experimentally determined parameters and are, in principle, able to predict the change in pH obtained for any related merocyanine photoacid.

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.

Evolution of catalytic machinery: three-component nanorotor catalyzes formation of four-component catalytic machinery

The three-component nanorotor [Cu2(S)(R)]2+ (k298 = 46.0 kHz) that is a catalyst for a CuAAC reaction binds the click product at each of its copper centers thereby creating a new platform and a dynamic slider-on-deck system. Due to this sliding motion (k298 = 65.0 kHz) the zinc-porphyrin bound N-methylpyrrolidine is efficiently released into solution and catalyzes a follow-up Michael addition.

"On-The-Fly" Non-Adiabatic Dynamics Simulations on Photoinduced Ring-Closing Reaction of a Nucleoside-Based Diarylethene Photoswitch

Nucleoside-based diarylethenes are emerging as an especial class of photochromic compounds that have potential applications in regulating biological systems using noninvasive light with high spatio-temporal resolution. However, relevant microscopic photochromic mechanisms at atomic level of these novel diarylethenes remain to be explored. Herein, we have employed static electronic structure calculations (MS-CASPT2//M06-2X, MS-CASPT2//SA-CASSCF) in combination with non-adiabatic dynamics simulations to explore the related photoinduced ring-closing reaction of a typical nucleoside-based diarylethene photoswitch, namely, PS-IV. Upon excitation with UV light, the open form PS-IV can be excited to a spectroscopically bright S₁ state. After that, the molecule relaxes to the conical intersection region within 150 fs according to the barrierless relaxed scan of the C1–C6 bond, which is followed by an immediate deactivation to the ground state. The conical intersection structure is very similar to the ground state transition state structure which connects the open and closed forms of PS-IV, and therefore plays a crucial role in the photochromism of PS-IV. Besides, after analyzing the hopping structures, we conclude that the ring closing reaction cannot complete in the S₁ state alone since all the C1–C6 distances of the hopping structures are larger than 2.00 Å. Once hopping to the ground state, the molecules either return to the original open form of PS-IV or produce the closed form of PS-IV within 100 fs, and the ring closing quantum yield is estimated to be 56%. Our present work not only elucidates the ultrafast photoinduced pericyclic reaction of the nucleoside-based diarylethene PS-IV, but can also be helpful for the future design of novel nucleoside-based diarylethenes with better performance.