Coumarin Derivative and Gold Nanoparticle Conjugate as a Selective Fluorescent Sensor for Mercury Ion in Real Sample.

A biphenyl based coumarin fluorescent molecule, N,N'-bis(7-diethylamino-2-oxo-2 H-chromen-3-yl)methylene)biphenyl-2-2'-dicarbohydrazide (molecule 1) has been synthesized and characterised. Photophysical studies of 1 exhibit solvent polarity dependent absorption and emission maxima. Citrate capped gold nanoparticles (AuNPs) have been mixed with molecule 1 for the preparation of AuNPs/1 conjugate. The association constant of the AuNPs/1 conjugate has been calculated to 4.54 × 104 M- 1. The AuNPs/1 conjugate has been found to detect Hg2+ ion selectively by fluorescence enhancement. While addition of molecule 1 into the solution of AuNPs, fluorescence intensity of 1 quenched. On addition of several monovalent, divalent and trivalent metal ion into the solution of AuNPs/1 conjugate separately, there was no change in fluorescence intensity of 1 has been observed. However, upon addition of Hg2+ ion into the solution of AuNPs/1 conjugate, the fluorescence intensity enhancement occurred, indicating released of 1 from the surface of AuNPs and probably aggregation of AuNPs took place in presence of Hg2+ ion. The AuNPs/1 conjugate has been found to have a detection limit of 2.3 × 10- 9 M for Hg2+ ion in aqueous solvent. Meanwhile, the AuNPs/1 conjugate have also been successfully applied for the determination of Hg2+ in real water samples.

Exploration of the impact of graphene oxide, acetylenic gemini, and CTAT on the photophysical and aggregation properties of dipolar coumarin 153.

Advanced spectroscopic techniques have been utilized to study the interaction between the laser dye coumarin 153 (C153) and graphene oxide (GO) nanoparticles. GO was synthesized using a modified Hummers' method and characterized by UV-vis spectroscopy, Raman laser spectroscopy, FTIR-ATR spectroscopy, FESEM, HR-TEM, and XRD techniques. The GO@C153 composite was formed by mixing two aqueous solutions of GO and C153 due to their strong interaction through stacking and hydrophobic interactions. In this case, GO acts as an effective fluorescence quencher for C153 molecules, which undergo H-type aggregation in the presence of GO. The Stern-Volmer equation and time-dependent fluorescence studies were utilized to analyse the mechanism of fluorescence quenching. According to the findings, both static and dynamic quenching processes are responsible for the reduction in fluorescence intensity. The effect of surfactants (both cetyltrimethylammonium p-toluenesulfonate (CTAT) and synthesized N,N'-dihexadecyl-N,N,N',N'-tetramethyl-N,N'-but-2-ynediyl-di-ammonium chloride (16-4-16)) on the aggregation and photophysical properties of the dye was investigated using surface tensiometry, conductometry, UV-vis absorption spectroscopy, steady-state fluorescence measurements, DLS, and time-dependent fluorescence spectroscopy. Surfactants change the microenvironment of the C153 dye, leading to spectrum shifting and a higher quantum yield, which causes a rapid rise in fluorescence intensity in the micellar medium. It has been noted that in a micellar medium rather than in an aqueous one, the luminous intramolecular charge transfer (ICT) state of C153 stabilises. Lastly, we investigated the photophysical behavior of the GO-C153-micelle ternary system and discovered that, in the presence of a micellar medium, the quenched and blue-shifted (H-type aggregation) fluorescence peak of C153 (in the presence of GO) began to intensify once more. The main goal of this work is to create an effective and fairly cost powerful fluorescence sensor. Additionally, the ternary system (GO-C153-micelle) analytical idea can be employed to identify the onset of micelle formation. In wastewater treatment analysis, the GO-C153-surfactant ternary system concept can also be used to regenerate the adsorbent (in this case, GO) from dye molecules by allowing the dye molecules to exit the adsorbent and enter the micellar medium.

Enhanced Excited-State Hydricity of Pd-H Allows for Unusual Head-to-Tail Hydroalkenylation of Alkenes.

Photoinduced enhancement of hydricity of palladium hydride species enables unprecedented hydride addition-like ("hydridic") hydropalladation of electron-deficient alkenes, which allows for chemoselective head-to-tail cross-hydroalkenylation of electron-deficient and electron-rich alkenes. This mild and general protocol works with a wide range of densely functionalized and complex alkenes. Notably, this approach also allows for highly challenging cross-dimerization of electronically diverse vinyl arenes and heteroarenes.

Photoredox Catalyzed Single C-F Bond Activation of Trifluoromethyl Ketones: A Solvent Controlled Divergent Access of gem-Difluoromethylene Containing Scaffolds.

Selective defluorinative functionalization of trifluoromethyl ketones is a long-standing challenge owing to the exhaustive mode of the process. To meet the demands for the installation of the gem-difluoromethylene unit for the construction of the molecular architectures of well-known pharmaceuticals and agrochemicals, a distinct pathway is thereby highly desirable. Here, a protocol is introduced that allows the divergent synthesis of gem-difluoromethylene group containing tetrahydrofuran derivatives and linear ketones via single C-F bond activation of trifluoromethyl ketones using visible-light photoredox catalysis in the presence of suitable olefins as trapping partner. The choice of appropriate solvent and catalyst plays a significant role in controlling the divergent behavior of this protocol. Highly reducing photo-excited catalysts are found to be responsible for the generation of α,α-difluoromethyl ketone (DFMK) radicals as the key intermediate via a SET process. This protocol also results in a high diastereoselectivity towards the formation of partially fluorinated cyclic ketal derivatives with simultaneous construction of one C-C and two C-O bonds. State-of-the-art DFT calculations are performed to address the origin of diastereoselectivity as well as the divergence of this protocol.

Interfacial Structure and Electrostatics Related to Solute Activity in a Model Anionic-Surfactant/Polymer Self-Assembly.

Polymer/surfactant composites are used in industry as an excipient for water-insoluble solutes. Such enhanced dissolution ability of composite media is related to the spontaneous formation of pre-micellar polymer surfactant aggregates (PS) at a magnitude of order lower than the surfactant critical micelle concentration in water. Combining electrochemical and spectroscopic studies, we investigate the microscopic interfacial structure (i.e., interface electrostatics and surface polarity) of PS formed in composite media. We establish that in a composite system, a mere change in the polymer concentration at a fixed surfactant concentration makes possible to regulate the counter-ion binding ability, surface potential, surface charge density, packing and surface polarity of the PS interface. Our study shows that the higher dissolution of water-insoluble nonionic solutes in composite media is driven by the depressing of surface charge density and polarity of the PS interface. A similar modulation of the PS interface acts as a barrier for the passive relocation of water-soluble charged solutes into the PS pseudo-phase. The time-resolved fluorescence anisotropy study allows us to underline the effect of surface charge modulation on the dynamical aspects of solutes at the PS interface.

Comparative studies on the aggregate formation of synthesized zwitterionic gemini and monomeric surfactants in the presence of the amphiphilic antipsychotic drug chlorpromazine hydrochloride in aqueous solution: an experimental and theoretical approach.

The formation of aggregates, which are widely used in the field of biochemistry and the medical industry, was studied with different compositions of alkyl betaine gemini surfactant (C14Ab) in conjugation with chlorpromazine hydrochloride (CPZ). The results were compared with those of a single-chain zwitterionic surfactant (C12DmCB) of the same type with CPZ. Dynamic light scattering (DLS), confocal laser scanning microscopy (CLSM), and transmission electron microscopy (TEM) methods were used to distinguish the aggregates for the CPZ/C14Ab system in aqueous solutions above a certain mole fraction of the drug CPZ (αCPZ = 0.2). Time-resolved fluorescence decay measurements of acridine orange revealed relative polarity near the head group regions of mixed micelle (CPZ/C14Ab and CPZ/C12DmCB) systems. The hydrophilic environment around the head group regions of the CPZ/C14Ab system was different from that in the case of the CPZ/C12DmCB system. On the other hand, several theoretical models were employed (Clint, Rubingh, Motomura, and SPB) for mixed micellar systems to elucidate the different interaction parameters. Such a systematic study of a zwitterionic gemini amphiphile and its interaction with other amphiphiles and an amphiphilic drug molecule is rare in the literature.

Stimuli-directed selective detection of Cu2+ and Cr2O72- ions using a pH-responsive chitosan-poly(aminoamide) fluorescent microgel in aqueous media.

In this work, the preparation of a pH-responsive fluorescent microgel, (NANO-PAMAM-CHT), is presented for the selective detection of Cu2+ and Cr2O72- ions. The NANO-PAMAM-CHT (nanosized polyaminoamide-chitosan microgel) is synthesized via aza-Michael addition reactions in a controlled and stepwise manner in water, using easily affordable starting materials like 1,4-diaminobutane, N,N'-methylene-bis-acrylamide, NIPAM and chitosan. NANO-PAMAM-CHT shows pH-responsive fluorescent properties, whereas the fluorescence intensity shows a pH-responsive change. Due to the selective fluorescence quenching, the microgel can detect both Cu2+ ions and Cr2O72- ions selectively at ambient pH in aqueous medium. Moreover, it can selectively differentiate between Cu2+ ion and Cr2O72- ions at pH ∼3 in water. The limits of detection for Cu2+ ions and Cr2O72- ions are reported as 16.9 µM and 2.62 µM, respectively (lower than the minimum allowed level in drinking water) at pH ∼7. Mechanistic study further reveals the dynamic quenching phenomenon in the presence of Cu2+ ions and static quenching in the presence of Cr2O72- ions.

A detailed assessment on the interaction of sodium alginate with a surface-active ionic liquid and a conventional surfactant: a multitechnique approach.

An investigation has been made on the interaction of a biodegradable anionic polyelectrolyte, sodium alginate (NaAlg), with two oppositely charged cationic surfactants, 1-hexadecyl-3-methyl imidazolium chloride (C16MImCl) and 1-hexadecyl triphenylphosphonium bromide (C16TPB), the former is a surface active ionic liquid (SAIL) and the latter a conventional surfactant over a wide concentration regime of the polyelectrolyte. Dual influence of electrostatic and hydrophobic interactions plays in this investigation when mixing surfactants with an oppositely charged polyelectrolyte. A number of different experimental techniques, e.g., conductometry, tensiometry, steady state and time resolved spectrofluorimetry, turbidimetry, isothermal titration calorimetry (ITC), dynamic light scattering (DLS), attenuated total reflection (ATR), high resolution transmission electron microscopy (HR-TEM) and fluorescence microscopy, have been implemented to get comprehensive information about the interaction of the oppositely charged polyelectrolyte and surfactants. Tensiometry study reveals the existence of several conformations of NaAlg influenced by different concentrations of surfactants titrated to it and these are abbreviated as critical aggregation concentration (cac), saturated concentration of polymer-surfactant complex (Cs) and finally extended critical micelle concentration due to the aggregation of the surfactant itself, appearing in chronological order from low to high concentrations of surfactants. Apart from tensiometry, these above concentrations have been well found and the values are well comparable when investigating polyelectrolyte-surfactant interaction by other physicochemical techniques as well. Irreversible phase separation of the oppositely charged polyelectrolyte-surfactant complex (PS-complex) occurs at higher polyelectrolyte concentration investigated here for both the surfactants in the vicinity of cac for C16MImCl and near for C16TPB and finally persists after further addition of surfactants above the formation of free micelles. Several bulk and interfacial parameters, viz., Gibbs free energy of micellization , enthalpy of micellization , entropy of micellization , degree of counterion binding (ß), surface excess at cmc (Γmax), area minimum (Amin), surface pressure at cmc (πcmc), pC20, packing parameter (P), hydrodynamic radius (r) and aggregation number (Na) of two surfactants both in the presence and absence of NaAlg, have been calculated for these investigated systems. Characterization of NaAlg, both surfactants and their individual complexes was performed using FTIR-ATR. DLS shows the distribution of size of polymer surfactant complexes over a wide range of surfactant concentrations at a fixed polyelectrolyte concentration, while HR-TEM study reveals not only the size of agglomerated clusters of the PS-complex but also its shapes. Images of NaAlg-surfactant complexes were also captured using fluorescence microscopy in solution phase. A strong PS-complex in the presence of C16MImCl has been reported here over C16TPB.

Origin of the Failure of Density Functional Theories in Predicting Inverted Singlet-Triplet Gaps.

Recent experimental and theoretical studies have shown several new organic molecules that violate Hund's rule and have the first singlet excited state lower in energy than the first triplet excited state. While many correlated single reference wave function methods have successfully predicted excited-state energetics of these low-lying states, conventional linear-response time-dependent density functional theory (TDDFT) fails to predict the correct excited-state energy ordering. In this article, we have explored the performance of combined DFT and wave function methods like doubles-corrected TDDFT and multiconfiguration pair-density functional theory for the calculation of inverted singlet-triplet gaps. We have also tested the performance of the excited-state DFT (eDFT) method for this problem. Our results have shown that it is possible to obtain inverted singlet-triplet gaps both by using doubles-corrected TDDFT with a proper choice of double-hybrid functionals or by using eDFT.

Magneto-Optical Stark Effect in Fe-Doped CdS Nanocrystals.

Fe2+ doping in II-VI semiconductors, due to the absence of energetically accessible multiple spin state configurations, has not given rise to interesting spintronic applications. In this work, we demonstrate for the first time that the interaction of homogeneously doped Fe2+ ions with the host CdS nanocrystal with no clustering is different for the two spin states and produces two magnetically inequivalent excitonic states upon optical perturbation. We combine ultrafast transient absorption spectroscopy and density functional theoretical analysis within the ground and excited states to demonstrate the presence of the magneto-optical Stark effect (MOSE). The energy gap between the spin states arising due to MOSE does not decay within the time frame of observation, unlike optical and electrical Stark shifts. This demonstration provides a stepping-stone for spin-dependent applications.

HFIP-Assisted Single C-F Bond Activation of Trifluoromethyl Ketones using Visible-Light Photoredox Catalysis.

A visible light photoredox catalytic method for the selective cleavage of single strong C-F bond in trifluoromethyl ketones is reported. Single electron reduction of trifluoromethyl ketones generates difluoromethyl radicals which can be engaged in intermolecular C-C bond formation with N-methyl-N-arylmethacrylamides to furnish fluorine-containing oxindole derivatives in good yields. The reaction shows excellent chemoselectivity with good functional group tolerance under mild conditions. 1,1,1,3,3,3-Hexafluoroisopropanol (HFIP) as a solvent plays a critical role for the selective single C-F bond cleavage. High-level DFT calculations are depicted to shed light on the mechanism.

Effect of Surfactant Tail Length on the Hydroxypropyl Cellulose-Mediated Premicellar Aggregation of Sodium n-Alkyl Sulfate Surfactants.

Polymer/surfactant composites have emerged as a subject of interest for their diverse applications. The improved solution properties in polymer/surfactant composites have been correlated to the formation of premicellar surfactant aggregate-polymer complexes (PS) at a surfactant concentration well below their critical micelle concentrations. Using different physicochemical and spectroscopic techniques here we have studied PS formed by hydroxypropyl cellulose, a nonionic-biocompatible polymer, and alkyl sulfate surfactants of different tail lengths. Our study shows that an increase in surfactant tail length eases PS formation and enhances PS-induced polymer cross-linking and, correspondingly, solution viscosity. PS consisting of shorter tail surfactants and those with longer tail surfactants differ microscopically as the former offers more polar interior than the later as evidenced from fluorescence measurements. Our study establishes that shorter tail surfactants intend to stay loosely packed inside PS and allow larger water penetration, which creates a relatively polar hydrophobic core compared to the PS with longer tail surfactants. The stronger packing of PS with longer tail surfactants is an outcome of favorable interaction between polymer polar groups and surfactant headgroups, which further creates strongly hydrogen-bonded water in their hydration shell.

Addressing the System-Size Dependence of the Local Approximation Error in Coupled-Cluster Calculations.

Over the last two decades, the local approximation has been successfully used to extend the range of applicability of the "gold standard" singles and doubles coupled-cluster method with perturbative triples CCSD(T) to systems with hundreds of atoms. The local approximation error grows in absolute value with the increasing system size, i.e., by increasing the number of electron pairs in the system. In this study, we demonstrate that the recently introduced two-point extrapolation scheme for approaching the complete pair natural orbital (PNOs) space limit in domain-based pair natural orbital CCSD(T) calculations drastically reduces the dependence of the error on the system size, thus opening up unprecedented opportunities for the calculation of benchmark quality relative energies for large systems.

How Exciton Interactions Control Spin-Depolarization in Layered Hybrid Perovskites.

Using circularly polarized broadband transient absorption, time-resolved circular photoluminescence, and transient Faraday rotation spectroscopy, we report that spin-dependent interactions have a significant impact on exciton energies and spin depolarization times in layered Ruddlesden-Popper hybrid metal-halide perovskites. In BA2FAPb2I7, we report that room-temperature spin lifetimes are largest (3.2 ps) at a carrier density of ∼1017 cm-3 with increasing depolarization rates at higher exciton densities. This indicates that many-body interactions reduce spin-lifetimes and outcompete the effect of D'yakonov-Perel precessional relaxation that has been previously reported at lower carrier densities. We further observe a dynamic circular dichroism that arises from a photoinduced polarization in the exciton distribution between total angular momentum states. Our findings provide fundamental and application relevant insights into the spin-dependent exciton-exciton interactions in layered hybrid perovskites.

Crystallographic Elucidation of Stimuli-Controlled Molecular Rotation for a Reversible Sol-Gel Transformation.

To get an idea about the most probable microporous supramolecular environment in the gel state, gelator molecule 1 has been crystallized from its gelling solvent (dimethylformamide). Crystal structure analysis of 1 shows a strong π···π stacking interaction between the electron-deficient pentafluorophenyl ring and electron-rich naphthyl ring. The gelling solvent situated in the "molecular pocket" stitches the gelators through weak H-bonding interactions to facilitate the formation of an organogel. Scanning electron microscopy analysis exhibits a ribbonlike fibrous morphology that resembles the supramolecular arrangement of 1 in its crystalline state, as evidenced by powder X-ray diffraction. In the presence of external stimuli (tetrabutylammonium fluoride), the organogel of 1 disassembles into sol. This sol-gel transformation phenomenon has been explained on the basis of X-ray single-crystal analysis. Single crystals obtained from the sol state show that naphthylic -OH of 1 gets deprotonated, resulting in C-C bond rotation that plays a major role in the sol-gel transformation. Gelator 1 exhibits weak green fluorescence in the gel state, whereas it shows highly intense yellow fluorescence in the sol state. Furthermore, a reversible sol-gel transformation associated with changes in the spectroscopic properties has been observed in the presence of acids and fluoride ions, respectively.

Combining Wave Function Methods with Density Functional Theory for Excited States.

We review state-of-the-art electronic structure methods based both on wave function theory (WFT) and density functional theory (DFT). Strengths and limitations of both the wave function and density functional based approaches are discussed, and modern attempts to combine these two methods are presented. The challenges in modeling excited-state chemistry using both single-reference and multireference methods are described. Topics covered include background, combining density functional theory with single-configuration wave function theory, generalized Kohn-Sham (KS) theory, global hybrids, range-separated hybrids, local hybrids, using KS orbitals in many-body theory (including calculations of the self-energy and the GW approximation), Bethe-Salpeter equation, algorithms to accelerate GW calculations, combining DFT with multiconfigurational WFT, orbital-dependent correlation functionals based on multiconfigurational WFT, building multiconfigurational wave functions from KS configurations, adding correlation functionals to multiconfiguration self-consistent-field (MCSCF) energies, combining DFT with configuration-interaction singles by means of time-dependent DFT, using range separation to combine DFT with MCSCF, embedding multiconfigurational WFT in DFT, and multiconfiguration pair-density functional theory.

Revised M11 Exchange-Correlation Functional for Electronic Excitation Energies and Ground-State Properties.

The ability of Kohn-Sham density functional theory (KS-DFT) to accurately predict various types of electronic excitation energies with (necessarily approximate) exchange-correlation functionals faces several challenges. Chief among these is that valence excitations are usually inherently multiconfigurational and therefore best treated by functionals with local exchange, whereas Rydberg and charge-transfer excitations are often better treated with nonlocal exchange. The question arises regarding whether one can optimize a functional such that all three kinds of excitations (valence, Rydberg, and charge transfer, including long-range charge transfer) are treated in a balanced and accurate way. The goal of the present work is to try to answer that question and then to optimize a functional with the best possible balanced behavior. Of the variety of functional types available, we choose to use a range-separated hybrid meta functional for the following reasons: (i) Range separation allows the percentage of Hartree-Fock (HF) exchange to change with interelectronic separation, and therefore, one can have 100% HF exchange at large interelectronic separations, which gives good performance for long-range charge-transfer excitations, while the range separation allows one to simultaneously have smaller values of HF exchange at small and intermediate interelectronic separations, giving good performance for valence and Rydberg excitations. (ii) Meta functionals allow one to obtain better accuracy with high HF exchange than is possible with functionals whose local part depends only on spin densities and their gradients. This work starts with the range-separated hybrid meta functional M11 and reoptimizes it (with strong smoothness restraints) against electronic excitation energies and ground-state properties to obtain a new functional called revM11 that gives good performance for all three types of electronic excitations and at the same time gives very good predictions across the board for ground-state properties.

A semiempirical effective Hamiltonian based approach for analyzing excited state wave functions and computing excited state absorption spectra using real-time dynamics.

We describe a new approach to extract information about an excited state wave function using a reduced orbital space molecular orbital decomposition approach for time-dependent density obtained from real-time dynamics. We also show how this information about the excited state wave function can be used to accelerate the convergence of real-time spectra and model excited state electron dynamics. We have combined this approach with our recent implementation of the real-time intermediate neglect of differential overlap for spectroscopy (INDO/S) to study the solvatochromic shift of Nile Red in acetone, ethanol, toluene and n-hexane solvents, and, for the first time, the excited state absorption spectra of coronene, 5,10,15,20-tetra(4-pyridyl)porphyrin (TPyP), zinc phthalocyanine, and nickel TPyP using a semiempirical Hamiltonian.

Ionic liquid mediated micelle to vesicle transition of a cationic gemini surfactant: a spectroscopic investigation.

In this contribution, we have examined a composition dependent self aggregated structural modification of a catanionic mixture of the surface active ionic liquid (IL) 1-butyl-3-methylimidazolium octyl sulphate and a cationic gemini surfactant (14-5-14) in aqueous medium. We have observed that the hydrodynamic diameter of the aggregates increases with increasing IL concentration and microscopic evidence (HRTEM, FESEM, and LCSM) shows the formation of vesicle like aggregates (Dh ≈ 200 nm) at XIL = 0.5. The steady state fluorescence anisotropy of the membrane binding probe DPH shows a micelle to vesicle transition at this composition. The viscosity of the solution shows a peak at XIL = 0.3, indicating the formation of a worm like micelle as an intermediate of the micelle to vesicle transition. The rotational dynamics shows a stiffer surfactant packing in the vesicles compared to the micelles, whereas, the solvation dynamics measurements indicate a higher abundance of bound type water in the vascular medium compared to that for the micelle. The formed vesicles also show stability towards temperature and biomolecules, which can be used for respective applications.

Synthesis and Characterization of Electron-Deficient Asymmetrically Substituted Diarylindenotetracenes.

Electron-deficient asymmetrically substituted diarylindenotetracenes were prepared via a series of Friedel-Crafts acylations, aryl-aryl cross-couplings, and an intramolecular oxidative cyclization to form the indene ring. Single-crystal X-ray experiments showed good π-π overlap with π-π distances ranging from 3.26 to 3.76 Å. Both thermogravimetric analysis and differential scanning calorimetry indicated that asymmetrically substituted indenotetracenes (ASIs) are stable at elevated temperatures. From cyclic voltammetry experiments, HOMO/LUMO energy levels of ASI derivatives were determined to be near -5.4/-4.0 eV. UV/visible absorption spectra showed strong absorption of light between 400 and 650 nm with molar attenuation coefficients from 104 to 105 M-1 cm-1. ASIs were also found to have very low fluorescence quantum yields, less than 4%. Using the solid-state packing determined from the single-crystal X-ray experiments, computational modeling indicated that ASI molecules should favor electron transport.