Ce-Doped Smart Adsorbentswith Photoresponsive Molecular Switches for Selective Adsorption and Efficient Desorption

Achieving efficient adsorption and desorption processes by controllably tuning the properties of adsorbents at different technical stages is extremely attractive.However,it is difficult for traditional adsorbents to reach the target because of their fixed active sites.Herein,we report on the fabrication of a smart adsorbent,which was achieved by introducing photoresponsive azobenzene derivatives with cis/trans isomers to Ce-doped mesoporous silica.These photoresponsive groups serve as “molecular switches”by sheltering and exposing active sites,leading to efficient adsorption and desorption.Ce is also doped to provide additional active sites in order to enhance the adsorption performance.The results show that the cis isomers effectively shelter the active sites,leading to the selective adsorption of methylene blue(MB)over brilliant blue(BB),while the trans isomers completely expose the active sites,resulting in the convenient release of the adsorbates.Both selective adsorption and efficient desorption can be realized controllably by these smart adsorbents through photostimulation.Moreover,the performance of the obtained materials is well maintained after five cycles.

Synthesis of Hymecromone Derivatives Containing Chiral 1,1'-Bi-2-naphthyl Moiety for Dual-mode Molecular Switch

Some hymecromone derivatives containing chiral 1,1'-bi-2-naphthyl moiety were synthesized and their photodimerizations were investigated. It was found that fluorescence intensity and optical rotation of the new chiral hymecromone derivatives could be regulated by light. This property has potential significance for developing a new type of dual-mode molecular switch.

Effect of Chirality on the Electronic Transport Properties of the Thioxanthene-Based Molecular Switch

Based on the nonequilibrium Green function method and density functional theory calculations, we theoretically investigate the effect of chirality on the electronic transport properties of thioxanthene-based molecular switch. The molecule comprises the switch which can exhibit different chiralities, that is, cis-form and trans-form by ultraviolet or visible irradiation. The results clearly reveal that the switching behaviors can be realized when the molecule converts between cis-form and trans-form. ~urthermore, the on-off ratio can be modulated by the chirality of the carbon nanotube electrodes. The maximum on-off ratio can reach 109 at 0.4 V for the armchair junction, suggesting potential applications of this type of junctions in future design of functional molecular devices.

Characterization of a Redox-responsive Molecular Switch Based on Dibenzo[1,2]dithiine Using DFT

Structural and electronic properties of a bistable redox-responsive molecular switch based on dibenzo[1,2]dithiine （PSBH） were studied using the DFT-B3LYP/6-31G＊ method. The results confirmed that the electrical conductivity of the closed form of considered molecular switch is higher than that of the open form. NBO electric charges on heavy atoms of biphenyl unit revealed that the positive charge on sulfur atoms reinforced, which caused the collapse of disulfide bond.

A Label-Free Colorimetric Aptasensor Containing DNA Triplex Molecular Switch and AuNP Nanozyme for Highly Sensitive Detection of Saxitoxin

Saxitoxin(STX),one of the most toxic paralytic shellfish poisons discovered to date,is listed as a required item of aquatic product safety inspection worldwide.However,conventional detection methods for STX are limited by various issues,such as low sensitivity,complicated operations,and ethical considerations.In this study,an aptamer-triplex molecular switch(APT-TMS)and gold nanoparticle(AuNP)nanozyme were combined to develop a label-free colorimetric aptasensor for the rapid and highly sensitive de-tection of STX.An anti-STX aptamer designed with pyrimidine arms and a purine chain was fabricated to form an APT-TMS.Specific binding between the aptamer and STX triggered the opening of the switch,which causes the purine chains to adsorb onto the surface of the AuNPs and enhances the peroxidase-like activity of the AuNP nanozyme toward 3,3’,5,5’-tetramethylbenzidine.Under optimized conditions,the proposed aptasensor showed high sensitivity and selectivity for STX,with a limit of detection of 335.6 pmol L^(−1) and a linear range of 0.59-150 nmol L^(−1).Moreover,good recoveries of 82.70%-92.66%for shellfish and 88.97%-106.5%for seawater were obtained.The analysis could be completed within 1 h.The proposed design also offers a robust strategy to achieve detection of other marine toxin targets by altering the corresponding aptamers.

Current–Voltage Characteristics of the Aziridine-Based Nano-Molecular Wires: a Light-Driven Molecular Switch

Using nonequilibrium Green＇s function formalism combined first-principles density functional theory, we analyze the transport properties of a 4,4-dimethyl-6-（4-nitrophenyl）-2-phenyl-3,5-diaza-bicyclo[3.1.0]hex-2-ene molecular optical switch. The title molecule can convert between closed and open forms by visible or ultraviolet irradiation. The I-V characteristics, differential conductance, on-off ratio, electronic transmission coefficients, spatial distribution of molecular projected self-consistent Hamiltonian orbitals, HOMO-LUMO gaps, effect of electrode materials Y（111）（Y =Au, Ag and Pt） on electronic transport and different molecular geometries corresponding to the closed and open forms through the molecular device are discussed in detail. Based on the results, as soon as possible the open form translates to the closed form, and there is a switch from the ON state to the OFF state（low resistance switches to high resistance）. Theoretical results show that the donor/acceptor substituent plays an important role in the electronic transport of molecular devices. The switching performance can be improved to some extent through suitable donor and acceptor substituents.

A Study on the Molecular Switch of Gene Expression of the Mouse Heart Nuclear DNA Fragments

It is observed by in situ stain that LDH (1 5) ...nNAD + can probably enter the nucleopore and can be bound bound specifically with the genes that encode them. During the in vitro expression, the dilution of heart nuclear DNA fragments could enhance the expression activity of LDH/DNA and the amount of expressed LDH (1 5) is in proportion to the amount of dissociable LDH (1 5) on the LDH/DNA. With the integration of 14C Leu to the proteins, it is also observed that the addition of LDH (1 5) ...nNAD + can suppress the in vitro expression activity of LDH/DNA. AFM observation shows that the regulation sequence at the both ends of active genes may be bound with such active factors as proteins encoded by the genes which probably is the main molecular switch of gene expression and regulation we have been always searching for. Our work shows the prospective application of the combination of AFM and isotope labeling in the research of biological reaction.

Electrically Driven Nonresonant Single Molecular Switches

Electrical switching of a single-molecule junction provides a practical module to perform sophisticated operations in electronic devices.However,designing an all-electrically-driven molecular switch is a great challenge.Here,we experimentally and theoretically investigated the charge transport characteristics of isoindigo(ISO)-molecules at the single-molecule level using the scanning tunneling microscope break junction technique.We find that the single-molecule junctions of ISO-molecules display bias voltage-driven switching characteristics.These switches are realtime,reversible,and nondestructive under low-bias voltages.Experimental results show that the mechanism of the switch is not the transition from nonresonant charge transport to resonant charge transport,but it is the shift of the frontier orbital energy levels of ISO-molecules and the change of the interfacial electronic coupling with bias voltage.Our results will advance the design of high-performance bias voltage-driven molecular switches.

Recent advances in new-type molecular switches

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

Label-free fluorescent strategy for sensitive detection of tetracycline based on triple-helix molecular switch and G-quadruplex

In this assay, a label-free fluorescent sensing platform based on triple-helix molecular switch（THMS） and G-quadruplex was developed for the detection of tetracycline. We demonstrated this approach by using THMS, which consists of a central section with a shortened 8-mer aptamer sequence with high affinity to tetracycline and flanked by two arm segments. G-rich oligonucleotide can specifically bind to thioflavin T（Th T） as a signal transduction probe（STP）. In the absence of tetracycline, THMS remains stable, the fluorescence of background is low. By the addition of target tetracycline, the aptamer-target binding results in the formation of a structured aptamer-target complex, which disassembles the THMS and releases the STP. The free STP self-assembles into G-quadruplex and specifically binds to Th T which generates a obvious fluorescence enhancement. Using the triple-helix molecular switch, the developed aptamer-based fluorescent sensing platform showed a linear relationship with the concentration of tetracycline ranging from 0.2 to 20.0 nmol/L. The detection limit of tetracycline was determined to be970.0 pmol/L. The assay avoids complicated modifications or chemical labeling, making it simple and cost-effective. So, it is expected that this aptamer-based fluorescent assay could be extensively applied in the field of food safety inspection.

Silicon-Based Molecular Switch Junctions

In contrast to the static operations of conventional semiconductor devices,the dynamic conformational freedom in molecular devices opens up the possibility of using individual molecules as new types of devices such as a molecular conformational switch or for molecular data storage.Bistable molecules such as those having two stable cis and trans isomeric confi gurations could provide,once clamped between two electrodes,a switching phenomenon in the non-equilibrium current response.Here,we model molecular switch junctions formed at silicon contacts and demonstrate the potential of such tunable molecular switches in electrode/molecule/electrode confi gurations.Using the non-equilibrium Green function(NEGF)approach implemented with the density-functional-based tight-binding(DFTB)theory,a series of properties such as electron transmissions,current voltage characteristics in the different isomer conformations,and potential energy surfaces(PESs)as a function of the reaction coordinates along the trans to cis transition were calculated for two azobenzene-based model compounds.Furthermore,in order to investigate the stability of molecular switches under ambient conditions,molecular dynamics(MD)simulations at room temperature were performed and time-dependent fl uctuations of the conductance along the MD pathways were calculated.Our numerical results show that the transmission spectra of the cis isomers are more conductive than trans counterparts inside the bias window for both model compounds.The currentvoltage characteristics consequently show the same trends.Additionally,calculations of the time-dependent transmission fluctuations along the MD pathways have shown that the transmission in the cis isomers is always signifi cantly larger than that in their trans counterparts,showing that molecular switches can be expected to work as robust molecular switching components.

A first-principles study of dihydroazulene as a possible optical molecular switch

By applying nonequilibrium Green's function formalism combined with first-principles density functional theory, we investigate the electronic transport properties of the dihydroazulene optical molecular switch. Three kinds of adsorption sites including the hollow, bridge and top sites are studied. The two forms of this molecule, namely the open form and the closed form, can reversibly switch from each other upon photoexcitation. Their transmission spectra are remarkably distinctive. Theoretical results show that the current of the closed form is always significantly larger than that of the open form for all three adsorption sites, which promises this system as possibly one of the good candidates for optical switches due to its unique advantage, and which may have some potential applications in the future molecular circuit.

Molecular Switches and Multiple Logic Gates Based on 4-（2-Pyridylazo）resorcinol

A simple-structured 4-（2-pyridylazo）resorcinol （PAR） system presents interesting properties with dual fluorescent outputs. Modulated by solution pH two kinds of reversible switch behaviors, ＂ON-OFF＂ and ＂OFF-ON＂, were realized with the PAR system. Stimulated by different combination of external stimulus, such as metal ions, UV ir- radiation and solution pH, the PAR system could perform multiple logic functions including three inputs AND, two inputs INHIBIT and combinatorial ＂NOR/AND＂ in parallel. The operation of the designed system is very simple and detected with a high sensitive fluorescent signal.

A Pillar[6]arene-[2]pseudorotaxane Based pH-Sensitive Molecular Switch

A novel pH-responsive[2]pseudorotaxane based on ethylated pillar[6]arene and bis(1,2,3-triazolium)butane cation was constructed.The dethreading and rethreading could be reversibly controlled by adding base and acid,i.e.,the deprotonation and reprotonation of the guest.In contrast,such responsible switching behavior does not occur for the complexation between the guest and ethylated pillar[5]arene,since both the cationic axle and the deprotonated one can be strongly bound by ethylated pillar[5]arene.Furthermore,the bis(1,2,3-triazolium)butane⊂pillar[6]-arene-[2]pseudorotaxane can also disassemble upon the addition of competitive ethylated pillar[5]arene.

Capped carbon nanotube-based molecular switch

Using the Landauer formalism that combines both the non-equilibrium Green's function (NEGF) and first-principles density functional theory (DFT), the electron transport characteristics of one-dimensional molecular switching device based on the capped carbon nanotubes have been investigated. The results show that the transmission can be efficiently tuned within two orders of magnitude just by changing 0.2 nm of the tube-tube separation. Moreover, the electron transport is insensitive to the topology of the facing conformations which can improve the practical stability of the chosen system as a molecular switch.

新型杂合四芳烯光控分子开关的设计合成与性能测试

围绕分子开关及聚集诱导发光的科研热点领域进行本科教学实验设计,将光致变色二芳烯巧妙嵌合于具有聚集诱导发光性能的四芳烯体系中,制备得到兼具变色和发光功能的新型杂合四芳烯光控荧光分子开关,科教融合,将科研前沿引入到本科实验教学。从物质的制备、分离提纯、结构表征和性能测试等方面进行了综合实验探索。本实验分子设计简练新颖,内容丰富,现象明显,在综合运用和巩固本科学习的基本理论和基本操作的基础上,激发学生的科研兴趣,培养团结协作和突破创新的科学精神。

靛红双氮二苯腙分子开关的光致异构化机理

腙类分子开关在超分子化学领域有非常重要的应用价值,基于靛红发色团发展出的新型腙类分子开关已被合成.因其具有可见光激发下的顺反异构化特征、衍生物的易合成性及对外界刺激的敏感性,其在生物化学领域具有重要的应用价值.然而,该新型分子开关的光致异构化机制尚不明确,异构过程是否存在新奇的现象也不得而知.本文采用基于半经验OM2/MRCI的轨迹面跳跃动力学方法,系统地研究了一种名为靛红双氮二苯腙分子开关E-Z异构化过程的光致异构化机理.研究发现该E构型分子开关的S_(1)激发态平均寿命约为107 fs,该分子开关的E-Z异构化量子产率为16.01%.通过对该分子开关光致异构化过程的计算,明确了两种不同分子开关异构化机制;除围绕C=N键旋转的传统分子开关异构机制之外,阐明了新的异构机制——分子开关转子部分面对面的扭转;通过时间分辨的荧光辐射谱的计算,预测了异构化过程中存在极快的荧光猝灭现象,并且伴随着荧光红移的发生;通过对计算得到的荧光光谱与激发态平均寿命的分析,提出了“暗态”的存在,并对“暗态”存在的原因给出了可能的解释.研究结果可为新型分子开关的设计及应用提供理论指导作用.

偶氮苯基小分子光控聚N-异丙基丙烯酰胺在离子液体中的自组装

偶氮苯基材料因其具有可逆的光致顺反异构特性,可调控聚合物的自组装行为而受到广泛关注。采用不同结构且广泛商业化的偶氮苯基小分子(偶氮苯(AZO)、对羟基偶氮苯(AZO-OH)、对氨基偶氮苯(AZO-NH2)、二甲基黄[AZO-N(CH_(3))_(2)])作为光分子开关,控制聚N-异丙基丙烯酰胺(PNIPAm)在1-乙基-3-甲基咪唑双(三氟甲基磺酰基)亚胺([C2mim][NTf_(2)])离子液体中的自组装行为,探讨不同偶氮苯基末端基元对于PNIPAm自组装相行为的影响。结果表明,偶氮苯基小分子均能有效调控PNIPAm在[C2mim][NTf_(2)]离子液体中的相变响应行为,但不同的末端基元对于PNIPAm的相变温度及相变区间影响甚微。结合原位变温红外谱图分析可知,紫外光照强化了PNIPAm与离子液体之间的相互作用,从而抑制了PNIPAm侧链间的相互聚集,这将促进紫外光照条件下“溶剂化”效应的发生,可获得更低的相变温度。

银-二芳基乙烯化合物的合成及其光致变色性质的研究

金属介导的分子开关配合物在有机光电功能材料及分子器件等领域具有广阔的应用前景。本工作通过配位导向机制将金属离子Ag I与二芳基乙烯开关L结合,制备一种银-二芳基乙烯配位化合物[L-AgNO_(3)]_(2)(CHCl_(3))_(2)(Ag-L)。其单晶结构表明,中心金属离子Ag I与L上不同位置的N原子发生配位作用形成一个扭曲的四面体。通过红外光谱(IR)及核磁共振氢谱(1H NMR)对其结构进行表征,利用紫外-可见分光光谱仪(UV-Vis)研究Ag-L的光致变色行为,探索了其在不同介质中的开闭环过程。一系列研究结果表明,Ag-L化合物在二氯甲烷溶液和聚甲基丙烯酸甲酯(PMMA)中均具有良好的可逆光致变色性质。

PHOTOSWITCHABLE NANOFLUOROPHORES FOR INNOVATIVE BIOIMAGING

Photosensitive fluorescent probes have become powerful tools in chemical biology and molecular biophysics,which are used to investigate cellular processes with high temporal and spatial resolution.Accordingly,photosensitive fluorescent probes,including photoactivatable,photoconvertible,and photoswitchable fluorophores,have been extensively developed during the past decade.The photoswitchable fluorophores have received much attention because they highlight cellular events clearly.This minireview summarizes recent advances of using reversibly photoswitchable fluorophores and their applications in innovative bioimaging.Photoswitchable fluorophores include photoswitchable fluorescent proteins,photoswitchable fluorescent organic molecules(dyes),and photoswitchable fluorescent nanoparticles.Several strategies have been developed to synthesize photoswitchable fluorophores,including engineering combination proteins,chemical synthesis,polymerization,and self-assembly.Here we concentrate on polymer nanoparticles with optically switchable emission properties:either fluorescence on/offor dualalternating-color fluorescence photoswitching.The essential mechanisms of fluorescence photoswitching enable different types of photoswitchable fluorophores to change emission intensity or wavelength(color)and thus validating the basis of the fluorescence on/offor dual-color photoswitching design.Generally the possible applications of any fluorophores are to label biological targets,followed by specific imaging.The newly developed photoswitchable fluorophores enable super-resolution fluorescence imaging because of their photosensitive emission.Finally,we summarize the important area regarding future research and development on photoswitchable fluorescent nanoparticles.