Solid-State Solvent-Independent Excited-State Intramolecular Proton Transfer in a Coordination Polymer and Its Temperature Dependence.

Increasing demand for futuristic switches and sensors around the world has created an intense interest in smart materials, which can show a rapid but feature-dependent change in the physical properties in the presence of external stimuli. Hitherto such changes in the photophysical property of materials, specifically in the solid state, are projected for the use of smart on-off switches. Materials having an external-stimuli-responsive change in the photophysical properties like excited-state intramolecular proton transfer (ESIPT) can also be utilized for these purposes. Although the event of solid-state ESIPT is not new in the domain of material chemistry, especially for organic molecules, it was never observed for coordination polymers (CPs). Previous instances of ESIPT in CPs have necessitated the presence of a solvent as a suspension medium, driving a solvent-assisted ESIPT phenomenon. However, the emergence of a solvent-independent ESIPT-enabled CP presents unique advantages. The well-defined periodic arrangement ensures reliable property variations, while the robust coordination bonds between the metal nodes and ligands provide durability in harsh environments. Addressing this gap, we present the first ever solid-state, solvent-free, and solvent-independent ESIPT-active CP. Remarkably, this CP exhibits temperature-dependent ESIPT on-off behavior, demonstrating its potential as a cutting-edge material in the field of smart switches and sensors.

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.

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).

Light and Cation-Driven Optical Switch based on a Stilbene-Appended Terpyridine System for the Design of Molecular-Scale Logic Devices.

A molecular system comprising a terpyridine moiety capable of coordinating with different cations and a photoswitchable stilbene unit has been utilized here for the fabrication of multiply configurable logic systems. Incorporation of a substituted stilbene unit into the terpyridine motif generates an intraligand charge-transfer-sensitive module whose absorption and emission spectral properties are highly sensitive to light as well as cations. On the basis of the optical response profile of the receptor in the presence of selected cations as well as light of a specific wavelength, we are able to demonstrate multiple Boolean logic functions such as INHIBIT, IMPLICATION, OR, NOR, and NAND, as well as various combinations of them. Of particular interest, we utilized the present system for the construction of security keypad locks and memory devices by maintaining a proper sequence of the stimuli and monitoring either absorption or emission spectral response at a specific wavelength as the output signal. In addition to various Boolean logic functions, the present system has also the ability to mimic fuzzy logic operations for generating an infinite-valued logic scheme depending on its emission spectral responses upon varying the concentration of cationic (Fe2+ and/or Zn2+) and anionic (CN-) inputs.

Stimuli-Responsive Molecular Switches and Logic Devices Based on Ru(II)-Terpyridyl-Imidazole Coordination Motif.

We report herein the synthesis, photophysics, and electrochemistry of three Ru(II)-terpyridine complexes derived from a new terpyridyl-imidazole ligand (tpy-HImzPh3F2) and study their pH- and temperature-responsive behaviors toward the fabrication of molecular switches. The complexes emitted at room temperature (RT) have a lifetime within the 4.5-49.0 ns domain, depending on the auxiliary ligand and the solvent used. In the acidic region, the complexes exhibit emission, indicating the "on-state", while in the basic condition, the emission is totally quenched, indicating the "off-state". Similarly, when the temperature is lowered, the emission intensity and lifetime are enhanced, demonstrating the on-state, while increase of temperature leads to quenching of the emission intensity and lifetime, designated as the off-state. In both cases, the process is reversible. The bathochromic shift of the spectral band together with the emission quenching and lowering of the Ru3+/Ru2+ potential is also observed upon deprotonation at elevated pH. In addition, systematic variation of the absorption spectral behaviors upon variation of pH helps in evaluation of the pKa's of the complexes. In essence, the complexes can act as switches emanated from a huge change in their absorption, emission, and redox behaviors as a function of their acidity/basicity (pH) and temperature. Moreover, their emission spectral responses as a function of pH and temperature were utilized for the fabrication of two-input binary logic gates. Density-functional theory (DFT) and time-dependent density-functional theory (TD-DFT) computations are performed for appropriate interpretation of the spectral bands.

The Art of Designing DNA Nanostructures with CAD Software.

Since the arrival of DNA nanotechnology nearly 40 years ago, the field has progressed from its beginnings of envisioning rather simple DNA structures having a branched, multi-strand architecture into creating beautifully complex structures comprising hundreds or even thousands of unique strands, with the possibility to exactly control the positions down to the molecular level. While the earliest construction methodologies, such as simple Holliday junctions or tiles, could reasonably be designed on pen and paper in a short amount of time, the advent of complex techniques, such as DNA origami or DNA bricks, require software to reduce the time required and propensity for human error within the design process. Where available, readily accessible design software catalyzes our ability to bring techniques to researchers in diverse fields and it has helped to speed the penetration of methods, such as DNA origami, into a wide range of applications from biomedicine to photonics. Here, we review the historical and current state of CAD software to enable a variety of methods that are fundamental to using structural DNA technology. Beginning with the first tools for predicting sequence-based secondary structure of nucleotides, we trace the development and significance of different software packages to the current state-of-the-art, with a particular focus on programs that are open source.

Exploitation of the Second Coordination Sphere to Promote Significant Increase of Room-Temperature Luminescence Lifetime and Anion Sensing in Ruthenium-Terpyridine Complexes.

This paper deals with the synthesis, characterization, and photophysical behaviors of three Ru(II)-terpyridine complexes derived from a terpyridyl-imidazole ligand (tpy-HImzPh3Me2), wherein a terpyridine moiety has been coupled with a dimethylbenzil unit through a phenylimidazole spacer. The three complexes display strong emission at RT having excited-state lifetimes in the range of 2.3-43.7 ns, depending upon the co-ligand present and the solvents used. Temperature-dependent emission spectral measurements have demonstrated that the energy separation between emitting metal-to-ligand charge transfer state and non-emitting metal-centered state is increased relative to that of [Ru(tpy)2]2+. In contrast to our previously studied Ru(II) complexes containing similar terpyridyl-imidazole motif but differing by peripheral methyl groups, significant enhancement of RT emission intensity and quantum yield and remarkable increase of emission lifetime occur for the present complexes upon protonation of the imidazole nitrogen(s) with perchloric acid. Additionally, by exploiting imidazole NH motif(s), we have examined their anion recognition behaviors in organic and aqueous media. Interestingly, the complexes are capable of visually recognizing cyanide ions in aqueous medium up to the concentration limit of 10-8 M. Computational studies involving density functional theory (DFT) and time-dependent DFT methods have been carried out to obtain insights into their electronic structures and to help with the assignment of absorption and emission bands.

Stimuli-Responsive Near-Infrared Emissive Os(II)-Terpyridine Complexes with a Sense of Logic.

Two bis-tridentate Os(II) compounds based on a heteroditopic terpyridine-bipyridine-type ligand were synthesized, and their photophysical properties were thoroughly studied. The compounds exhibit strong spin-allowed 1MLCT bands in the visible domain (489-521 nm) as well as weak 1GS to 3MLCT bands within the 668-815 nm domain. The compounds display strong luminescence from the 3MLCT state in the near-infrared domain (728-780 nm) at room temperature having lifetimes in the range of 20.0-171.0 ns. After coordination of [Os(tpy-PhCH3/H2pbbzim)2]2+ unit to the terpyridine site of tpy-Hbzim-dipy, the complexes offer vacant pyridine-imidazole motifs for interacting with cationic and anionic guests. Consequently, photophysical properties of the compounds were tuned to a great extent upon interaction with selected cations, anions, pH, as well as protons. Anion-induced alteration of the ground- and excited-state properties of the compound lead to recognition of specific anions in solution. Significant change in the optical spectral behaviors as well as switching of emission spectral properties of the compounds was done in the NIR region upon treating with anions, cations, protons, and solvents (dichloromethane, acetonitrile, methanol, dimethylsulfoxide, and water). Moreover, the optical outputs in response to external stimuli were used to demonstrate binary functions of two-input IMPLICATION, NOR, and XNOR logic gates.

Long-Lived Trimetallic Complexes of Fe(II), Ru(II), and Os(II) Based on a Heteroditopic Bipyridine-Terpyridine Bridge: Synthesis, Photophysics, and Electronic Energy Transfer.

Synthesis, characterization, and investigation of photophysical and redox behaviors of a new class of homo- and heterotrimetallic complexes of composition [(bpy/phen)2Ru(dipy-Hbzim-tpy)M(tpy-Hbzim-dipy)Ru(bpy/phen)2]6+ (M = FeII, RuII, and OsII) derived from a conjugated heteroditopic bipyridine-terpyridine bridge were carried out in this work. Trimetallic RuZnRu complexes of composition [(bpy/phen)2Ru(dipy-Hbzim-tpy)Zn(tpy-Hbzim-dipy)Ru(bpy/phen)2]6+ were also synthesized in situ as their photophysical properties are of particular interest in demonstrating the absorption and emission spectra of the complexes in the presence of a metal (Zn2+) that has neither metal-to-ligand charge transfer (MLCT) nor metal-centered (3MC) states. Complexes display intense absorption bands spanning almost the entire UV and visible region. The complexes also exhibit rich electrochemical behaviors with a number of metal-centered reversible oxidation and ligand-centered reduction waves. All complexes are luminescent at room temperature, and time-resolved emission spectral studies indicate that peripheral RuII-centered emissive 3MLCT states are quantitatively quenched, by intramolecular energy transfer to the low lying 3MLCT (for central Ru and Os) or 3MC states of the FeII center (nonluminescent). Interestingly, Fe(II) does not adversely deteriorate the photophysics of the RuFeRu assembly. Thus, multicomponent complexes in the present work can serve as well-organized light-harvesting antennas as the light absorbed by multiple chromophoric subunits is efficiently channeled to the distinct component having the lowest-energy excited state.

Doping Mn(II) in All-Inorganic Ruddlesden-Popper Phase of Tetragonal Cs2PbCl2I2 Perovskite Nanoplatelets.

Doping Mn(II) in inorganic Ruddlesden-Popper phase Cs2PbCl2I2 perovskite nanoplatelets is reported. The host nanostructures were prepared with a calculative protocol taking the exact required composition of Cs(I) and Pb(II) and injecting the preformed mixed oleylammonium chlorides and iodides at optimized reaction temperature. Reactions were optimized with various halides and their mixtures, but the stable phase of the Cs2PbX4 system was obtained only for the chloride-iodide mixed-halide system. Introduction of Mn(II) along with Pb(II), resulted in successful light-emitting doped nanocrystals. Measuring the photoluminescence and the decay lifetimes at room and liquid nitrogen temperatures, the variations in the excitonic, self-trapped, and Mn dopant emission properties were compared with those of the chalcogenide and perovskite nanocrystals.

Stimuli-Responsive Luminescent Bis-Tridentate Ru(II) Complexes toward the Design of Functional Materials.

We report here the synthesis, characterization, and photophysics of two bis-tridentate Ru(II) complexes based on a heteroditopic ligand and thoroughly studied their stimuli-responsive behaviors toward the design of functional materials. Both complexes display emission at room temperature having lifetimes in the range of 0.5-70.0 ns, depending on coligand and solvent. Substantial modulations of absorption and emission spectral behaviors of the complexes were done upon interaction with anions, and anion-induced changes in the properties lead to recognition of selected anions in both organic and aqueous media. Photophysical properties of the complexes were also tuned by changing the pH of the medium, and p Ka values in both ground and excited states were determined. The presence of free pyridine-imidazole motifs in the complexes leads to substantial modulation of the optical properties and switching of the emission properties upon interaction with selected cations as well as with protons. Fe2+, Co2+, Ni2+, and Cu2+ trigger emission quenching, while Zn2+ induces finite enhancement of the emission intensity in the complexes. In essence, modulation of the optical properties and switching of luminescence properties of the complexes were accomplished by a variety of the external stimuli such as anions, cations, protons, and pH, as well as solvent polarity. Importantly, the optical outputs in response to an appropriate set of stimuli were utilized to mimic the functions of two-input IMPLICATION, NOR, and XNOR logic gates.

Ru-Os dyads based on a mixed bipyridine-terpyridine bridging ligand: modulation of the rate of energy transfer and pH-induced luminescence switching in the infrared domain.

A series of heterobimetallic complexes of compositions [(bpy/phen)2Ru(dipy-Hbzim-tpy)Os (tpy-PhCH3/H2pbbzim)]4+ (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, tpy-PhCH3 = 4'-(4-methylphenyl)-2,2':6',2''-terpyridine and H2pbbzim = 2,6-bis(benzimidazole-2-yl)pyridine)), derived from a heteroditopic bpy-tpy bridging ligand, were synthesized and thoroughly characterized in this work. The heterometallic complexes exhibit two successive one-electron reversible metal-centered oxidations corresponding to OsII/OsIII at lower potential and RuII/RuIII at higher potential. All the four dyads exhibit very intense, ligand centered absorption bands in the UV region and moderately intense MLCT bands in the visible region. The dyads also show intense infrared emission with the emission maximum spanning between 734 nm and 775 nm with reasonably long room temperature lifetimes varying between 30 ns and 104 ns. Both steady state and time resolved luminescence spectroscopic investigations indicate that efficient and fast intramolecular energy transfer from the 3MLCT state of the Ru(ii) center to the Os-center takes place in all the four dyads. In addition, the rate of energy transfer was found to depend on the terminal ligand on the Os-site. Due to the presence of a number of imidazole NH protons in the dyads, significant modulation of both the ground and excited state properties of the complexes was made possible by varying the pH of the solution. By varying the terminal ligand, pH-induced "on-off", "off-off-on" and "on-off-on" emission switching of the complexes was nicely demonstrated in the infrared region.