Pyronin B Research Articles

Improving the Brightness of Pyronin Fluorophore Systems through Quantum-Mechanical Predictions.

The pyronin class of fluorophores serves a critical role in numerous imaging applications, particularly involving preferential staining of RNA through base pair intercalation. Despite this important role in molecular staining applications, the same set of century-old pyronins (i.e., pyronin Y (PY) and pyronin B (PB)), which possess relatively low fluorophore brightness, are still predominantly being used due to the lack of methodology for generating enhanced variants. Here, we use TD-DFT calculations of interconversion energies between structures on the S1 surface as a preliminary means to evaluate fluorophore brightness for a proposed set of pyronins containing variable substitution patterns at the 2, 3, 6, and 7 positions. Using a nucleophilic aromatic substitution/hydride addition approach, we synthesized the same set of pyronins and demonstrate that quantum-mechanical computations are useful for predicting fluorophore performance. We produced the brightest series of pyronin fluorophores described to date, which possess considerable gains over PY and PB.

Molecular aggregates of pyronin dyes with polyelectrolyte polystyrene sulfonate (PSS) in aqueous solution

Aggregation of the cationic dyes pyronin B (PyB) and pyronin Y (PyY) in aqueous solution containing anionic polyelectrolyte polystyrene sulfonate (PSS) has been studied by using steady-state and time-resolved fluorescence and UV–vis absorption spectroscopy techniques. Although H-aggregates of these pyronin dyes have been previously observed in colloidal suspension, this is the first report of their J-aggregates obtained as a function of dye concentration by using constant concentration of PSS in solution. The best dye concentrations for the J-aggregates were determined as 2.4 × 10−5 M and 1.2 × 10-4 M for PyB and PyY, respectively. Moreover, aggregation equilibrium constants (KD) and thermodynamic functions were determined as a function of temperature for H-type aggregation. By employing the exciton theory, angle (α) between the molecular transition dipole moments and the long aggregate axis, and the intermolecular distance (R) were also calculated for each dye aggregates. In addition, the fluorescence lifetime values were determined from fluorescence decay measurements for the monomer and aggregated species of pyronin compounds in polyelectrolyte aqueous solution.

Evaluation of a novel woody waste obtained from tea tree sawdust as an adsorbent for dye removal

In this work, the evaluation of low-cost, abundantly available, efficient and eco-friendly bio-waste adsorbent (BWA) obtained from waste tea stem (sawdust tea wood) was presented as an alternative to the current expensive methods of removing Pyronin B (PyB) dye from aqueous solution. The effects of varied factors, amount of adsorbent, initial dye concentration, contact time, etc., were studied, and optimal experimental conditions were revealed. The Langmuir isotherm model gave a better conformity than the Freundlich model with 3.85 mg/g as maximum adsorption capacity at 25 °C. In addition, structural and morphological characterization of BWA was confirmed by FTIR, SEM study. It was found that the Lagergren’s model could be used for the estimation of the system’s kinetics. The present investigation and comparison with other reported adsorbents concluded that BWA may be applied as an attractive low-cost option for removal of PyB from aqueous solution.

P-type doped ambipolar polymer transistors by direct charge transfer from a cationic organic dye Pyronin B ferric chloride

We report a facile way to improve organic field effect transistor (OFET) performance based on low concentration doping of diketopyrrolopyrrole-thieno[3,2-b]thiophene (DPPT-TT) solution by an organic cationic dye, Pyronin B (PyB). DPPT-TT OFETs show significantly high field effect mobilities (up to 3.5 cm2 V−1 s−1) by optimizing the doping ratio and solvent selection. The devices also exhibit better on/off ratio by suppression of n-channel characteristics. Ultraviolet photoelectron spectroscopy and UV–vis absorption spectra revealed efficient p-type doping in PyB doped DPPT-TT films, which was confirmed by the Fermi level shifting toward the highest occupied molecular orbital and red shift of the absorption spectrum.

The thin films of pyronin dyes doped with poly(vinyl sulphate) on glass substrate: Preparation and characterization

The thin films of pyronin B (PyB) and pyronin Y (PyY) mixed with poly(vinyl sulphate) (PVS) on glass substrate from aqueous solution were fabricated using a simple spin-coating film technique. The photophysical properties of the thin films were examined by UV–Vis, steady-state fluorescence and time-resolved fluorescence spectroscopy techniques. The dye thin films on the glass substrate were prepared at various [PVS]/[dye] ratios. The interactions of pyronin dyes with PVS caused the formation of monomeric and H-aggregate thin films of the dyes. H-aggregates of pyronin dyes in the thin film quenched their fluorescence intensities while the monomeric dye films have strong fluorescence. Moreover, the presence of H-aggregates in the thin film also decreased the fluorescence lifetimes of dyes. The morphological variations in the thin films depending on the dye concentration were investigated by AFM. The morphological analysis of the thin films revealed that the thin films including H-aggregates were predominant in fibril-like structures while the monomeric thin films displayed the same morphologies compared to that observed in pristine PVS film. When the spectroscopic and morphological results were evaluated, it was concluded that H-aggregates of pyronin dyes were formed due to the adsorption of the dyes on PVS backbone.

Photophysical and adsorption properties of pyronin B in natural bentonite clay dispersion

The present study focused on the adsorption and photophysical properties of pyronin B (PyB) in bentonite aqueous dispersion. The photophysical properties of PyB in the aqueous dispersion were studied by using UV–vis absorption, steady-state and time-resolved fluorescence spectroscopy techniques. In this concept, the interaction of the dye with bentonite particles in the aqueous dispersion was spectroscopically followed depending on certain parameters such as interaction time, pH and the dye concentration. Obtained spectral data revealed that the aggregate structures (H-type) of PyB in the aqueous dispersion were formed in the dye concentration range studied. The non-fluorescence nature of H-aggregates and the clay minerals governed the fluorescence property of PyB. The mentioned non-radiative processes caused the fluorescence lifetime of the dye to decrease compared to that in water. The adsorption process of PyB on bentonite was examined depending on contact time and initial adsorbate concentration. An adsorption isotherm was good-fitted by the Freundlich model with a linear regression correlation value of 0.999. The adsorption of PyB on bentonite particles was in agreement with pseudo second-order kinetics.

The Fluorescence Properties of Three Rhodamine Dye Analogues: Acridine Red, Pyronin Y and Pyronin B

The fluorescence spectra, fluorescence quantum yield, and fluorescence lifetime of Acridine Red (AR), Pyronin Y (PYY), and Pyronin B (PYB) in aqueous and organic solvents were measured by steady state fluorescence, time-correlated single photon counting, and electronic absorption methods. The rate constants of radiation and non radiation process (kf and kic) were calculated to elucidate the structural effect on the fluorescence mechanism. The data for each compound are compared with that of the corresponding rhodamine dye. AR showed significant longer lifetime and higher quantum yield than PYY and PYB, because the alkyls on N atom enhance the internal conversion (IC), the longer the alkyl the faster the IC. However, the structural variation does not alter the rate constant of radiation process (kf) but does change kic significantly. The phenyl in Rhodamine B or Rhodamine 6G shows only a slight effect on the fluorescence properties. Ethanol is the solvent in which all five compounds exhibit longest lifetime and highest fluorescence quantum yield.

Photophysical properties of pyronin dyes in reverse micelles of AOT

The photophysical properties of pyronin B (PyB) and pyronin Y (PyY) in reverse micelles formed with water/sodium bis (2-ethyl-1-hexyl) sulfosuccinate (AOT)/n-heptane were investigated by UV–vis absorption, steady-state and time-resolved fluorescence spectroscopy techniques. This study was carried out a wide range of reverse micelle sizes, with hydrodynamic radii ranging from 1.85 to 9.38nm. Significant photophysical parameters as band shifts, fluorescence quantum yields and fluorescence lifetimes were determined to understand how photophysical and spectroscopic features of the dye compounds were affected by the variation of reverse micelle sizes. In this regard, control of reverse micelle size by changing W0, the molar ratio of water to surfactant, allowed tuning the photophysical properties of the dyes in organic solvent via reverse micelle. Non-fluorescent H-aggregates of pyronin dyes were observed for the smaller reverse micelles whereas an increase in the reverse micelle size induced an increment in the amount of dye monomers instead of dye aggregates. Thus, the fluorescence intensities of the dyes were improved by increasing W0 due to the predomination of the fluorescent dye monomers. As a result, the fluorescence quantum yields also increased. The fluorescence lifetimes of the dyes in the reverse micelles were determined by the time-resolved fluorescence decay studies. Evaluation of the fluorescence lifetimes calculated for pyronin dyes in the reverse micelles showed that the size of reverse micelle affected the fluorescence lifetimes of pyronin dyes.

Growth of large single MOF crystals and effective separation of organic dyes

Through the optimization of synthesis conditions, we obtained large Cu3(BTC)2 crystals with a diameter of 2–4 mm. Such large crystals could be utilized as “chromatographic columns” for effective separation of organic dyes such as thionine (TH) and pyronin B (PB). It was found that the concentration of hydron was the key factor to obtain the large pure crystals. This strategy could be used to grow other hydrophilic MOFs.

The effect of poly(vinyl alcohol) on the photophysical properties of pyronin dyes in aqueous solution: A spectroscopic study

The photophysical properties of pyronin B (PyB) and pyronin Y (PyY) in water and poly(vinyl alcohol) (PVA) aqueous solutions were studied by using absorption, steady-state fluorescence and time-resolved fluorescence spectroscopy techniques at room temperature. The spectroscopic and photophysical properties of pyronin dyes in the concentrated PVA aqueous solution were different than those found in water. The aggregation of the pyronin dyes in the concentrated PVA aqueous solution was prevented with ease while the dye aggregation was generally formed in water with high dye concentration. The decrease in the aggregation tendency of pyronin dyes in the concentrated PVA aqueous solution caused an increase in radiative transitions. The addition of PVA into the aqueous solution induced the enhancement in the fluorescence intensity of the dyes compared to those in water. As a result, the quantum yields of the dyes were improved by the addition of PVA at high loading. The time-resolved fluorescence study revealed that the fluorescence decay of dyes in all solutions were found to be single-exponential and the fluorescence lifetime of pyronin dyes in the concentrated PVA aqueous solution were also higher than those found in water.

A spectroscopic study of water-soluble pyronin B and pyronin Y in Langmuir–Blodgett films mixed with stearic acid

Mono and multilayer of water-soluble pyronin B (PyB) and pyronin Y (PyY) mixed with stearic acid (SA) have been incorporated in Langmuir–Blodgett (LB) films. The surface pressure–area (π–A) isotherm studies pointed out that pure PyB and PyY are incapable of forming stable films at air–water interface and collapsed readily at low surface pressures. However, mixture of PyB or PyY with SA easily formed stable films at the air–water interface and they were easily transferred onto solid substrates. The average area per molecule of mixed films of PyB and PyY at the air–water interface was observed to decrease with increasing concentrations of PyB and PyY. The spectroscopic characteristics of PyB and PyY in chloroform, in SA containing chloroform and in LB films have also been investigated by using absorption and steady-state and time-resolved fluorescence spectroscopy techniques. The morphology of the LB film surfaces has been characterized by using atomic force microscopy (AFM).

An investigation of energy transfer between coumarin 35 and xanthene derivatives in liquid medium

The energy transfer between coumarin 35 (C35) and pyronin compounds, which are xanthene derivatives, i.e. pyronin B (PyB) and pyronin Y (PyY), in methanol was investigated at room temperature by using steady-state absorption, emission, and time-resolved fluorescence spectroscopy. Fluorescence energy transfer rate constants (k_T) and critical radius (R_0) were determined for C35-PyB and C35-PyY molecular pairs in methanol. The obtained values of k_T and R_0 indicated that the dipole-dipole interaction between C35-PyB and C35-PyY molecular pairs accounted for the energy transfer mechanism. The energy transfer efficiency and the distance between the donor and acceptor (r) were also calculated for donor-acceptor pairs using Förster's theory.

Effect of surfactants on the aggregation of pyronin B and pyronin Y in aqueous solution

Molecular dynamics of pyronin B (PyB) and pyronin Y (PyY) in aqueous solution containing different surfactants were investigated by using absorption and fluorescence spectroscopy techniques. First, the interactions of PyB and PyY with the negatively charged surfactant sodium dodecyl sulphate (SDS) were investigated in the below and above critical micelle concentration (cmc). The H-aggregate formation of the dye compounds was observed for below the cmc of SDS surfactant. The absorbance of H-aggregate absorption band of PyB and PyY decreased according to the aggregate–monomer equilibrium by increasing SDS surfactant concentration towards the cmc. Therefore, equilibrium constants of the aggregate formation and oscillator strengths of monomer and aggregate of the dye compounds were calculated from spectral studies. Moreover, aggregate formation dynamics was discussed in terms of thermodynamic functions by using temperature studies. The interactions of PyB and PyY with the positively charged hexadecyltrimethylammonium bromide (CTAB) and neutral Triton X-100 (TX-100) were also studied and it was observed that there was no aggregate formation on the absorption and fluorescence spectra for below and above the cmc.

Molecular n-Type Doping of 1,4,5,8-Naphthalene Tetracarboxylic Dianhydride by Pyronin B Studied Using Direct and Inverse Photoelectron Spectroscopies

Molecular n-type doping of 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTCDA) by pyronin B (PyB) is investigated using ultraviolet photoelectron spectroscopy (UPS), inverse photoelectron spectroscopy (IPES), and current–voltage (I–V) measurements. Deposition of small amounts (< 2 Å) of PyB on pristine NTCDA films leads to a shift of all the molecular levels away from the Fermi level by nearly 0.20 eV, indicative of n-type doping of NTCDA by PyB. Interface and bulk energy levels of films formed by co-evaporation of host and dopant show similarly efficient n-doping. The spectroscopic measurements are confirmed by I–V measurements, which show a four-orders-of-magnitude increase in current in doped films. The comparison of data obtained from UPS of the neat PyB film with the results of density functional theory calculations confirm that two species of PyB are evaporated and condensed into the solid state, with one species primarily responsible for doping.

Molecular excitons of Pyronin B and Pyronin Y in colloidal silica suspension

The electrostatic interactions of the cationic dyes Pyronin B (PyB) and Pyronin Y (PyY) with the negatively charged colloidal silica was investigated by molecular absorption and steady state fluorescence spectroscopy. Both dyes indicated changes in the absorption and emission spectra upon interaction with colloidal silica. A blue shift was observed in the absorption spectra for both dyes with increased dye concentration when the colloidal silica concentration was kept constant. These new bands observed that are higher energy than monomer bands are due to H-aggregates and they were analyzed by using exciton theory and monomer–dimer equilibrium.

Fluorimetric studies of solutions of pyronin dyes: equilibrium constants in water and partition coefficients in organic-solvent—water systems

The cytotoxic pyronin dyes provide simplified models for the xanthene squeleton of popular rhodamines. Kinetic analysis of fluorescence spectra of pyronin Y (PY) and pyronin B (PB) aqueous solutions allows us to study the reversible equilibria between R + zwitterions (λ Fluo, max=566 nm (PY), 570 nm (PB)) and colorless ROH xanthydrols (λ Fluo, max=463 nm (PY), 467 nm (PB)) formed through ion-pair reactions with nucleophile OH −. The rate and equilibrium constants of R + hydrolysis by OH − in water gives pK R+(S 0)= -2.6 for the two pyronins while fluorescent species are too short lived for any shift in the equilibrium to be detected in the S 1 state. Covalent ROH species are stable in basic solutions and poor ion solvating solvents; the reaction of R + with OH − is slow in neutral solutions. For further understanding and applications of pyronins on biomembranes, biphasic mixtures of an organic solvent (OS) with water (W) provide partition coefficients P and extraction percentages E of the different species in the OS phase. In the n-octanol-water (ratio 1:1) system, R + and ROH co-exist in both phases, resulting in P ion=1.8 (PY) and 2.6 (PB) at physiological pH with E ROH=0.09 (PY) and 0.16 (PB); most pyronin exists as R + in water owing to its pK R+ but the presence of the octanol phase shifts the equilibrium toward ROH. The ROH structure presents other features of interest because of its oxidization by air into RO xanthone in aprotic non-polar solvents. In the OS-W system (1:1) where OS is cyclohexane, the partitioning of pyronins between the OS and W phases is strongly one sided with R + remaining in water RO(λ Fluo, max=365–366 nm) completely trapped in the cyclohexane. The E percentages differ for PY and PB since E RO(PY)=0.8 but only 0.3 for PB. The implication of hydrophobic interactions and hydrogen-bonded (solvated) water in OS is also discussed.