Dye Molecules In Solution Research Articles

Freezing of Water Solvation Dynamics in Nanoconfinement by Reverse Micelles at Room Temperature.

Much attention has recently been paid to anomalously low dielectric constants of nanoconfined water between two slabs at room temperature (Fumagalli et al. Science, 2018, 360, 1339). These low values imply that the dipole rotation of the interfacial water on the slab is completely suppressed. Such freezing has so far been observed for water confined between solids. In contrast, it remains unclear whether this holds for water in soft confinement, which is omnipresent naturally and artificially. Here, we address this question using encapsulated reverse micelles with a dye molecule, allowing us to study water sandwiched between the surfactant and dye molecules in solution. Moreover, we examine the solvation related to the dielectric property of water, which is reorientational motion in the hydration layer of the dye molecule, by persistent hole-burning spectroscopy. We first show that the dye molecule is surrounded by water without contact with the surfactant and that the dye molecule has two or three hydration layers on average. We next demonstrate that the solvation dynamics is frozen below the water droplet size of ∼4 nm, whereas they become liquid-like when the RM size is further increased. The average gap distance (∼1.5 nm) for freezing the solvation agrees with the gap distance with no rotational water motions between slabs. Our findings may have biological relevance, providing a new aspect for understanding biological function in cells.

Boosting the Brightness of Raman Tags Using Cyanostar Macrocycles.

Raman probes have received growing attention for their potential use in super-multiplex biological imaging and flow cytometry applications that cannot be achieved using fluorescent probes. However, obtaining strong Raman scattering signals from small Raman probes has posed a challenge that holds back their practical implementation. Here, we present new types of Raman-active nanoparticles (Rdots) that incorporate ionophore macrocycles, known as cyanostars, to act as ion-driven and structure-directing spacers to address this problem. These macrocycle-enhanced Rdots (MERdots) exhibit sharper and higher electronic absorption peaks than Rdots. When combined with resonant broadband time-domain Raman spectroscopy, these MERdots show a ∼3-fold increase in Raman intensity compared to conventional Rdots under the same particle concentration. Additionally, the detection limit on the concentration of MERdots is improved by a factor of 2.5 compared to that of Rdots and a factor of 430 compared to that of Raman dye molecules in solution. The compact size of MERdots (26 nm in diameter) and their increased Raman signal intensity, along with the broadband capabilities of time-domain resonant Raman spectroscopy, make them promising candidates for a wide range of biological applications.

Mechanisms of dyes adsorption on titanium oxide– graphene oxide nanocomposites

Graphene oxides (GOs), synthesized with different oxidation degrees and associated with Titanium dioxide (TiO2) nanoparticles show efficient adsorption processes for dye molecules in solution. The structural, morphology, electronic and optical features of the nanocomposites were investigated by dedicated methods. Water remediation was investigated through the adsorption efficiency of methylene blue (MB) dye as a function of the nanocomposites concentration from 1 to 5 g/L in solutions. While pristine TiO2 showed a maximum removal of ∼44%, the incorporation of the GO ensures the fast and complete elimination of MB within 9 min. The ball milling process contributed to the increase in the number of defects and surface area in the nanocomposites, which was demonstrated by ID/IG ratios by Raman spectroscopy and surface areas by BET. Pseudo-second-order and mechanistic kinetic models were considered, and the performed analysis points out the relevance of the pseudo-second-order model to account for the adsorption kinetics. The Langmuir and Freundlich isotherm models were applied to the experimental data to find an adequate model to describe the adsorption equilibrium, as well as the intra-particle diffusion model during the different adsorption stages involved in the TiO2/GO nanocomposites. The role of the oxidation degree of GO was clarified through their respective efficiency in the removal of the dyes.

Principles of modeling the fluorescence spectral dynamics of dye molecules in solutions

FSDS is Fluorescence Spectral Dynamics Simulator, designed to investigate photoinduced charge transfer and its manifestations in time-resolved fluorescence spectra of a dye in a solvent. The project is implemented in C, using the MPI library. The computer model simulates stationary absorption and fluorescence spectra, as well as the time evolution of population distributions along the solvent reaction coordinate, to calculate spectral dynamics. Excitation and relaxation of intramolecular high-frequency vibrations are described at the quantum level. FSDS can fit the physical parameters of the dyes to experimental data. The dye excitation is consistently described accounting for the finite duration of the pump pulse. The program code implements two evolutionary models: a spin-boson model within the harmonic potential and a stochastic model based on the Smoluchowski diffusion operator for an arbitrary free energy surface. Computer simulation shows the numerical coincidence of the calculations performed in the framework of these models for the harmonic free energy surface. The detail description of the code and numerical schemes are presented. Program summaryProgram Title: Fluorescence Spectral Dynamics Simulator (FSDS)CPC Library link to program files:https://doi.org/10.17632/d39rrrkvhr.1Code Ocean capsule:https://codeocean.com/capsule/6544976Licensing provisions: GPLv3Programming language: CSupplementary material: Sample configuration files, User ManualNature of problem: The time-resolved spectra contain reach information about photochemical processes. However, the chemically important information about separate elementary processes is entangled due to they proceed in parallel. Time-resolved spectra modeling allows extracting information about these processes. The presented program code makes it possible to determine the relaxation characteristics of the solvent and the times of intramolecular relaxation.Solution method: Finite-difference time-domain and Brownian dynamics simulation methods.

Dual-Frequency Comb Transient Absorption: Broad Dynamic Range Measurement of Femtosecond to Nanosecond Relaxation Processes.

We experimentally demonstrate a dual-frequency comb-based transient absorption (DFC-TA) technique, which has a 12 fs time resolution and an ultrafast scan rate. Here, the fast scan rate is achieved by employing asynchronous optical sampling (ASOPS), which utilizes two independent mode-locked lasers with a slightly detuned repetition rates. The ASOPS approach is advantageous because photodegradation damage of optical sample during TA measurements can be minimized by a gated sampling. We show that the vibrational and electronic population relaxations of near-IR dye molecules in solution that occur in the time range from femtoseconds to nanoseconds can be resolved even with a single time scan measurement. The phase coherent nature of our dual-frequency comb lasers is shown to be the key for successful coherent averaging with femtosecond time resolution preserved over many data acquisitions. We anticipate that the present DFC-TA method without using any pump-probe time delay devices could be of use in developing ultrafast TA-based microscopy and time-resolved coherent multidimensional spectroscopy.

3D Oxidized Graphene Frameworks: An Efficient Adsorbent for Methylene Blue

Extraordinary properties of graphene and its derivatives have found application in varied areas such as energy, electronics, optical devices and sensors, to name a few. Large surface area along with specialized functional groups make these materials attractive for removal of dye molecules in solution via adsorption. Industrial effluents contain large amounts of toxic chemicals resulting in pollution of water bodies, which pose environmental hazards in general. Here we report application of 3D oxidized graphene frameworks in the efficient removal of cationic dye molecules such as methylene blue via adsorption. Systematic parametric studies investigating the effect of the initial dye concentration, pH and contact time have been performed. Spectroscopic analysis of the filtrate suggests that tortuous paths in 3D oxidized graphene frameworks result in efficient removal of dye molecules due to enhanced interaction. The hydroxyl groups retained in these 3D oxidized graphene frameworks facilitate adsorption of the dye molecules while passing through the adsorbent. pH studies suggest that maximum removal efficiency for methylene blue was achieved at pH value of 9. The results suggest that these 3D oxidized graphene frameworks can be used for purification of large volumes of contaminated water from cationic dyes in waste water treatment plants.

Excitation-emission Fourier-transform spectroscopy based on a birefringent interferometer

The correlation of molecular excitation and emission events provides a powerful multidimensional spectroscopy tool, by relating transitions from electronic ground and excited states through two-dimensional excitation-emission maps. Here we present a compact, fast and versatile Fourier-transform spectrometer, combining absorption and excitation-emission fluorescence spectroscopy in the visible. We generate phase-locked excitation pulse pairs via an inherently stable birefringent wedge-based common-path interferometer, retaining all the advantages of Fourier-transform spectroscopy but avoiding active stabilization or auxiliary tracking beams. We employ both coherent and incoherent excitation sources on dye molecules in solution, with data acquisition times in the range of seconds and minutes, respectively.

Solar Generation of Ion Gradients Using Dye-Sensitized Ion-Exchange Membranes

Most solar energy conversion technologies generate power through transport of energized electron particles; however, the physics that describes these technologies only requires that the particles be charged and not specifically that they are electrons. My research group studies solar energy conversion technologies that generate power from sunlight through ion transport. In my presentation I will report on my research group’s recent demonstration of ion transport against concentration gradients driven by solar illumination of dye-sensitized ion-exchange materials. Mechanistically, visible light was used to drive endergonic excited-state proton transfer from a covalent photoacid-functionalized polymer membrane. Photoacid molecules convert the energy in light into a change in the chemical potential of protons via a weakening of protic functional groups on the photoacid, i.e. a drop in its pK a. As a model system for ion-channels in polymer-electrolyte ion-exchange membranes, dye-sensitized conical nanopores in poly(ethylene terephthalate) (1 – 108 pores/cm2) were investigated. Remarkably, in a region occupied by ~20 zeptoliters (~2 x 10-20 L) of aqueous electrolyte, electrochemistry was used to determine the number of binding groups of the dyes and the ground-state pK a of the dyes, and fluorescence microscopy was used to determine the conditions where excited-state proton transfer occurred. These data were consistent with a hypothesis that pK a values of the photoacids in the ground-state and excited-state were significantly smaller than those measured for dye molecules in solution, likely due to incomplete screening of surface charges in the confined nanopores. Dye-sensitized Nafion monopolar ion-exchange membranes and bipolar ion-exchange membranes were also investigated. Under sunlight-simulated illumination these materials were found to exhibit photovoltaic action, i.e. generation of a photocurrent and a photovoltage. Bipolar membranes are a class of polymeric ion-exchange materials that consist of a monopolar cation-exchange membrane that is in intimate contact with a monopolar anion-exchange membrane. They are unique among the ion-exchange membranes in that they that separate and maintain pH differences across the membrane even during passage of ionic current. Moreover, the physics of ion equilibration processes within these membranes resembles that which occurs during equilibration of semiconductor pn-junctions. This body of work represents an underexplored solar energy conversion process that is being pioneered by my research group to operate via a mechanism similar to that in semiconductor pn-junctions. The applicability and practicality of these materials as standalone ionic photoelectrochemical devices will also be presented.

Characterizing the Solvated Structure of Photoexcited [Os(terpy)₂](2+) with X-ray Transient Absorption Spectroscopy and DFT Calculations.

Characterizing the geometric and electronic structures of individual photoexcited dye molecules in solution is an important step towards understanding the interfacial properties of photo-active electrodes. The broad family of “red sensitizers” based on osmium(II) polypyridyl compounds often undergoes small photo-induced structural changes which are challenging to characterize. In this work, X-ray transient absorption spectroscopy with picosecond temporal resolution is employed to determine the geometric and electronic structures of the photoexcited triplet state of [Os(terpy)2]2+ (terpy: 2,2′:6′,2″-terpyridine) solvated in methanol. From the EXAFS analysis, the structural changes can be characterized by a slight overall expansion of the first coordination shell [OsN6]. DFT calculations supports the XTA results. They also provide additional information about the nature of the molecular orbitals that contribute to the optical spectrum (with TD-DFT) and the near-edge region of the X-ray spectra.

Adsorption of reactive green 19 from water using polyaniline/bentonite

Polyaniline/bentonite was used in this study to investigate its adsorption behaviors of reactive green 19. Influencing factors including contact time, pH, temperature and inorganic salts were investigated. The adsorption kinetic data fitted the pseudo-second-order model better than the pseudo-first-order and Elovich models, and the Langmuir model was better than the Freundlich model to describe the adsorption process. Thermodynamic studies indicated that the adsorption of reactive green 19 by polyaniline/bentonite was an endothermic and spontaneous process. Experimental data indicated that both NaCl and Na2SO4 could improve the reactive green 19 adsorption as a result of aggregation of the dye molecules in solution induced by the inorganic salts, and an increase of pH value from 5 to 9 caused a slight decrease in reactive green 19 adsorption.

Measuring correlated electronic and vibrational spectral dynamics using line shapes in two-dimensional electronic-vibrational spectroscopy.

Two-dimensional electronic-vibrational (2DEV) spectroscopy is an experimental technique that shows great promise in its ability to provide detailed information concerning the interactions between the electronic and vibrational degrees of freedom in molecular systems. The physical quantities 2DEV is particularly suited for measuring have not yet been fully determined, nor how these effects manifest in the spectra. In this work, we investigate the use of the center line slope of a peak in a 2DEV spectrum as a measure of both the dynamic and static correlations between the electronic and vibrational states of a dye molecule in solution. We show how this center line slope is directly related to the solvation correlation function for the vibrational degrees of freedom. We also demonstrate how the strength with which the vibration on the electronic excited state couples to its bath can be extracted from a set of 2DEV spectra. These analytical techniques are then applied to experimental data from the laser dye 3,3'-diethylthiatricarbocyanine iodide in deuterated chloroform, where we determine the lifetime of the correlation between the electronic transition frequency and the transition frequency for the backbone C = C stretch mode to be ∼1.7 ps. Furthermore, we find that on the electronic excited state, this mode couples to the bath ∼1.5 times more strongly than on the electronic ground state.

Rapid Energy Transfer Enabling Control of Emission Polarization in Perylene Bisimide Donor-Acceptor Triads.

Materials showing rapid intramolecular energy transfer and polarization switching are of interest for both their fundamental photophysics and potential for use in real-world applications. Here, we report two donor-acceptor-donor triad dyes based on perylene-bisimide subunits, with the long axis of the donors arranged either parallel or perpendicular to that of the central acceptor. We observe rapid energy transfer (<2 ps) and effective polarization control in both dye molecules in solution. A distributed-dipole Förster model predicts the excitation energy transfer rate for the linearly arranged triad but severely underestimates it for the orthogonal case. We show that the rapid energy transfer arises from a combination of through-bond coupling and through-space transfer between donor and acceptor units. As they allow energy cascading to an excited state with controllable polarization, these triad dyes show high potential for use in luminescent solar concentrator devices.

Facile synthesis of fluorescent polymer nanoparticles by covalent modification-nanoprecipitation of amine-reactive ester polymers.

Emission wavelength control in fluorescent nanoparticles (NPs) is crucial for their applications. In the case of inorganic quantum dots or dye-impregnated silica NPs, such a control is readily achieved by changing the size of the particles or choosing appropriate fluorescent dyes, respectively. A similar modular approach for controlling the emission wavelength of fluo-rescent polymer NPs, however, is difficult. This article reports on fluorescent polymer NPs, the synthesis of which provides a platform for a modular approach towards the preparation of fluorescent NPs of desired emission wavelength. Atom-transfer radical polymerization (ATRP) is employed to synthesize reactive ester polymers, which are then easily modified with a commercially available dye and subsequently subjected to nanoprecipitation. The resulting NPs, with low size polydispersity, show an enhanced emission quantum yield when compared with the same dye molecules in solution.

Exploring Drug Diffusion through a Membrane: A Physical Chemistry Experiment for Health and Life Sciences Undergraduate Students

The transport of molecules across biological membranes are critical for most cellular processes. Membrane permeability is also a key determinant for drug absorption, distribution, and elimination. Diffusion, that is, the migration of matter down a concentration gradient, is a simple mechanism by which both endogenous and drug molecules can enter (or exit) cells. This paper describes a simple and engaging physical chemistry undergraduate laboratory experiment for health and life sciences students studying diffusion of drug and dye molecules in solution. In this experiment, the diffusion of amitriptyline hydrochloride, ranitidine hydrochloride, and tartrazine across a cellulose dialysis membrane is evaluated using an innovative macro and microscale approach. Compound concentration in solution as a function of time is obtained both from conductivity measurements of 25 mL solutions and from absorbance measurements of 100 μL samples taken in a 96-well microplate. By using solutions of different concentrations, the permeability coefficient of the membrane and the diffusion coefficient of the tested compounds are determined. Comparison of both methods, which yield similar values, is performed, which shows that either one of the approaches is suitable to independently conduct the experiment. On the basis of diffusion phenomena, the important pharmaceutical issue of absorption and transport of drugs through passive diffusion across biological or artificial membranes is presented.

Lasing from fluorescent protein crystals.

We investigated fluorescent protein crystals for potential photonic applications, for the first time to our knowledge. Rod-shaped crystals of enhanced green fluorescent protein (EGFP) were synthesized, with diameters of 0.5-2 μm and lengths of 100-200 μm. The crystals exhibit minimal light scattering due to their ordered structure and generate substantially higher fluorescence intensity than EGFP or dye molecules in solutions. The magnitude of concentration quenching in EGFP crystals was measured to be about 7-10 dB. Upon optical pumping at 485 nm, individual EGFP crystals located between dichroic mirrors generated laser emission with a single-mode spectral line at 513 nm. Our results demonstrate the potential of protein crystals as novel optical elements for self-assembled, micro- or nano-lasers and amplifiers in aqueous environment.

Photophysical and photochemical properties of HITC indotricarbocyanine dye molecules in solutions

Results of studies on the photonics of HITC indotricarbocyanine dye molecules with I–, Br–, and ClO4 – counterions were presented. Introduction of an additional salt (tetrabutylammonium bromide) (10–2 M) to slightly polar solutions of the tricarbocyanine dye was shown to cause significant changes in the dye photophysical and photochemical characteristics. It was concluded based on a comparison of HITC dye photophysical properties with I–, Br–, and ClO4 – counterions in slightly polar dichlorobenzene and highly polar EtOH; an analysis of trends in HITC photobleaching in deoxygenated and air-saturated solutions; and data from femtosecond spectroscopy that the features of the photophysical and photochemical processes in slightly polar dichlorobenzene were due to superfast charge transfer in tight ion pairs followed by formation of free radicals.

Coordinated shifts of interfacial energy levels: insight into electron injection in highly efficient dye-sensitized solar cells

Coordinated shifts on the order of ∼100 meV were found in the interfacial energy levels of ruthenium dye molecules and the conduction band of nano-crystalline TiO2. The shifts were induced by potential-determining additives used in highly efficient dye-sensitized solar cells. The observation of comparable shifts of interfacial energy levels in dye/TiO2 films is beyond the conventional understanding of the varied quantum efficiency of interfacial electron injection, which had been derived under the assumption of the band shift only in TiO2. Based on general physical concepts, we advanced the understanding of the electron injection mechanism and attributed the variable electron injection efficiency to the influence of potential-determining additives on the interfacial electronic structures of both the dyes and TiO2. Our results revealed that the interfacial dipole layer affected the electronic coupling between the donor states in photo-excited dyes and the acceptor states in TiO2, which led to changes in electron injection. The present model also explains the correlation between the radiative recombination, an important loss mechanism in solar cells, of photo-excited states of the anchored dye/TiO2 in operational cells and that of free dye molecules in solution. We also found the amount of coordinated shifts to be most likely related to the number of COOX groups in ruthenium dyes and metal-free organic dyes. This relationship implies that the effect of coordinated shifts in ruthenium dyes/TiO2 is one of the most probable reasons why these dyes enable higher performance than do metal-free organic dyes, in which the latter only have relatively small coordinated shifts. This discovery provides deeper insight into the interfacial electron injection mechanism and points out the importance of the realignment effect on interfacial energy levels in highly efficient dye-sensitized solar cells.

Photocatalytic activity of Ag/CuO/WO3 under visible-light irradiation

The photocatalytic activity of silver and copper oxide loaded WO3 nanocomposite (Ag/CuO/WO3) was investigated under visible-light using the decolorization of Acid Red 88 (AR 88) dye molecules in solution. The activity of WO3 nanoparticles (NPs) was significantly improved by the binary loading of Ag and CuO as cocatalysts. The photocatalytic mechanism was investigated to understand the enhanced photocatalytic activity, which was mainly attributed to the synergistic effect of the Ag and CuO binary cocatalysts loaded on the WO3 NPs. The Ag cocatalyst acted as an electron trapping center that enhanced electron/hole separation and the CuO cocatalyst significantly promoted four-electron reduction of oxygen for H2O production. The concurrent oxidation of organic dye molecules occurring on WO3 NPs was probably initiated at photogenerated holes with a high oxidation potential. To further improve the photocatalytic activity of the Ag/CuO/WO3 system, WO3 nanotubes (NTs) were synthesized and loaded with Ag and CuO. The photocatalytic activity of Ag/CuO/WO3 NTs in the decolorization of AR 88 after 180 min was approximately 1.5 and 6.4 times greater than that of Ag/CuO/WO3 NPs and N–TiO2, respectively.

Non-degenerated photoluminescence excitation correlation spectroscopy using an optical sampling technique

We have developed a highly time-resolved photoluminescence spectroscopy based on the excitation correlation method. Successive irradiation of a pair of ultrashort light pulses with different wavelength combinations taken from two sub-picosecond lasers has exposed both temporal and energetic correlation in photoluminescence intensity associated with a nonlinear response of a sample. An optical sampling technique has been introduced successfully in order to avoid consideration of the synchronization control of ultrashort light pulses. We have demonstrated the abilities of this technique by applying to the nonlinear photoluminescence dynamics of organic dye molecules in solution.

Removal of Reactive Red 198 from aqueous solution by Potamogeton crispus

Native, acid and alkali pretreated dried Potamogeton crispus ( P. crispus) was used for adsorption of Reactive Red 198 from aqueous solution. Effects of physicochemical environment on adsorption were investigated. The surface charge of the native, acid and alkali treated biomass were determined to be zero at pH 4.6, 3.8 and 4.1 ± 0.1, respectively. Adsorption capacity of native biomass was increased with alkali treatment against native and acid pretreated biomass. The maximum adsorption capacities ( q max) at 20 °C of native, acid and alkali pretreated biomass were determined as 14.3, 26.8 and 44.2 mg g −1, respectively. FT-IR analysis shows that P. crispus has many functional groups such as COO, S O, C–N, N–H. These functional groups can react with dye molecule in solution. Pseudo-second-order and intraparticle diffusion kinetic models are applicable adsorption of RR198 by P. crispus since adsorption of RR198 is complex and involves more than one mechanism.