Fluorescence Lifetime Of Dye Research Articles

Control of near-infrared dye fluorescence lifetime in all-polymer microcavities

The authors demonstrate photoluminescence lifetime and intensity control in a near-infrared dye embedded in all-polymer microcavity.

Active laser medium for near-infrared spectral range based on electron-unsymmetrical polymethine dye and silver nanoparticles

An effect of silver nanoparticles (Ag NPs) on spectral luminescent and lasing properties of an electron-unsymmetrical polymethine dye in ethanol solution has been studied. Fluorescence of the dye is characterized by a large Stokes shift of 3007 cm−1 and a quantum yield Φf of 0.08. An increase in the absorption cross section and in the fluorescence quantum yield of the dye molecules is observed in the presence of Ag NPs. The dye fluorescence lifetime of 1.11 ns remains unchanged after the addition of Ag NPs to the solution. Stimulated emission with spectrally pronounced two-mode oscillations has been obtained for the dye in the region of its fluorescence band maximum. A stimulated emission threshold is achieved on the average at 3.35 MW/cm2. The presence of Ag NPs leads to the enhanced intensity and 28% lowered threshold of dye stimulated emission. The data obtained can be used to develop new near-infrared lasing media.

Universal guidelines for the conversion of proteins and dyes into functional nanothermometers.

In the last decade, technological advances in chemistry and photonics have enabled real-time measurement of temperature at the nanoscale. Nanothermometers, probes specifically designed to relay these nanoscale temperature changes, provide a high degree of temperature, temporal, and spatial resolution and precision. Several different approaches have been proposed, including microthermocouples, luminescence and fluorescence polarization anisotropy-based nanothermometers. Anisotropy-based nanothermometers excel in terms of biocompatibility because they can be built from endogenous proteins conjugated to dyes, minimizing any system perturbation. Moreover, the resulting fluorescent proteins can retain their native structure and activity while performing the temperature measurement, allowing precise temperature recordings from the native environment or during an enzymatic reaction in any given experimental system. To facilitate the future use of these nanothermometers in research, here we present a theoretical model that predicts the optimal sensitivity for anisotropy-based thermometers starting with any protein or dye, based on protein size and dye fluorescence lifetime. Using this model, most proteins and dyes can be converted to nanothermometers. The utilization of these nanothermometers by a broad spectrum of disciplines within the scientific community will bring new knowledge and understanding that today remains unavailable with current techniques.

Absorption coefficient dependent non-linear properties of thin film luminescent solar concentrators

This research article studied absorption coefficient dependent losses and efficiency of thin film luminescent solar concentrator (LSC). The optimum absorption coefficient was determined by fabricating red dye doped thin film LSCs with varying absorption coefficients of 24–202 cm-1. The optical, electrical, and ray-trace model predicted results were compared to establish the optimum absorption coefficient for fabricated thin film LSCs. The optical and electrical efficiencies of thin film LSCs are a function of absorption coefficient; follow linearly at lower values, gradually becoming non- linear at higher values of absorption coefficient which restricts the overall efficiency. The multi layered ray–trace model predicted results deviated from the experimental results at high absorption coefficient. Non-linearity was introduced by losses mechanism of re-absorption, resonant energy transfer (RET), and scattering in thin film LSCs. Re-absorption losses were found to be dependent on optical path-length and absorption coefficient of thin film. They were identified and quantified through locally collected emission and optical path-length in thin film LSCs. Re-absorption losses caused a red shift in emission peak by ≈ 20 nm as the absorption coefficient increased from 24 to 202 cm-1. RET decreased fluorescence life time of dye from 5 ns to 2 ns for the absorption coefficient increased from 24–202 cm-1. These absorption coefficient dependent losses limit the optical and electrical efficiency of thin film LSC devices, and compared with bulk LSC.

Artefact-free Evaluation of Metal Enhanced Fluorescence in Silica Coated Gold Nanoparticles

Metal nanoparticles can either quench or enhance the emission of dyes in their vicinity, but the precise measurement and understanding of this effect is still hindered by experimental artifacts, especially for particles in colloidal dispersion. Here, we introduce a new methodology to correct the inner filter effect of the metal on the dye emission. To test the method, we developed new hybrid nanoparticles with a gold core and a silica shell of precise thickness (tuned from 7 to 13 nm), with a high quantum yield perylenediimide dye on the surface. This novel approach effectively avoids fluorescence quenching, allowing us to measure emission enhancements of 5 to 30 times, with no change on the dye fluorescence lifetime. Being able to measure the emission enhancement in dye-metal hybrid nanoparticles in dispersion, free from inner filter and quenching artifacts, offers excellent prospects to guide the development of more efficient fluorescent probes, sensors and photonic devices.

Fluorescence Quenching of Sulfo­rhodamine Dye over Graphene Oxide and Boron Nitride Nanosheets

AbstractWe report the fluorescence quenching of sulforhodamine 640 (SR 640) supported on graphene oxide (GO) and boron nitride (BN) nanosheets (NSs). The synthesis and characterization of both materials are described. X‐ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), transmission and scanning electron microscopy (TEM and SEM), and the Brunauer–Emmett–Teller (BET) method were used. The photophysical properties, such as the fluorescence lifetime and anisotropy of the SR dye over the synthesized materials, are reported. The observed fluorescence quenching of the SR dye over GO and BN occurs through an electron‐transfer process. Fluorescence decay analysis of SR revealed different behavior in the presence of GO and BN NSs. Adsorption of the dye on GO NSs leads to a non‐fluorescent complex, whereas adsorption of the dye on BN NSs results in quenching induced by a decrease in the fluorescence lifetime of the dye.

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.

Pore size dependence of self-assembled type photonic crystal on dye-sensitized solar cells efficiency utilising Chlorine e6

There are few reports on photoelectric conversion efficiency using naturally-occurring dyes for dye-sensitized solar cells (DSSC). This is because the matching with an excited electronic level of naturally-occurring dye to the conduction band of semiconductor is problematic; the excited electrons are easily relaxed to the steady state with fluorescence or heat emission. We examined the fluorescence inhibition effect of a self-assembled photonic crystal using Chlorine e6 dye. Chlorine e6 is derived from chlorophyll and has a long excited electron lifetime. We prepared TiO2 inverse opals with various particle sizes by liquid phase deposition and described their effect on DSSCs with regard to structural, optical and electrochemical properties. In addition, we explored the implications of fluorescence lifetime measurements relative to the photonic band diagram and the amount of adsorbed dye. Although the main factor affecting the external photoelectric conversion efficiency was the diffusion resistance of the electrolyte and the contact resistance between TiO2 interfaces, the possibility that the dye fluorescence lifetime, i.e. the photonic band structure, can affect the internal quantum efficiency per one dye molecule was also investigated.

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.

Time-resolved scanning system for double reflectance and transmittance fluorescence imaging of diffusive media

In this work we present a novel diffuse fluorescence imaging system, based on time-resolved two-wavelength double reflectance and transmittance setup for slab geometry samples. We describe the hardware setup, showing its compactness and versatility and show the results on preliminary measurements on phantoms. We fully assessed the performances and the dynamic ranges of the system. We validated its ability of recovering the optical properties of the bulk medium, for samples with scattering and absorption coefficients similar to those of biological tissues and with thicknesses of about 2 cm. Moreover we assess the linearity of the recorded signals against the fluorophore concentration, when it is homogeneously diffused in the phantom or concentrated inside a sealed inclusion. In both cases we observe again a fairly good linearity, over three orders of magnitude, from 10(-8)M to 10(-5)M. With the fluorescent inclusion we were also able to assess the imaging capabilities of the system, in terms of spatial resolution, which we appraise in about 3 mm, and in terms of imaging sensitivity (the smallest quantity of fluorescent dye distinguishable from the homogeneous background), settled to 200 fmol. Since the recorded data are time resolved, we could also estimate the dye fluorescence lifetime and build early and late time gate images. We finally discuss some of the criticalities of the proposed system and the developments we are currently carrying on in order to adapt it for in vivo measurements.

Controlling the fluorescence lifetime of dyes in nanostructured geometries

In this paper we show that the coupling of common red/near infrared emitting dyes with a well-defined photonic environment, comparable to Drexhage's structure, is effective to enhance or inhibit the molecular spontaneous emission rate. The fluorescent dye molecules were adsorbed at the air–polystyrene interface and spaced at known distances (20–200 nm) from the polystyrene–silver interface. The experimental decay rates of molecules were successfully modelled using a classical electrodynamics model that treats the emitter as a forced, damped electric dipole oscillator interacting with its nanoenvironment through its near field. Our results help establish a basis for characterising near-fields in nano-optics and controlling fluorescing species.

New indolium and quinolinium dyes sensitive to aqueous halide ions at physiological concentrations

AbstractTwelve new highly fluorescent dyes have been produced by the reaction of two heterocyclic nitrogen bases with 8‐bromooctanoic acid, 11‐bromoundecanoic acid and 15‐bromopentadecanoic acid. The bromide counter ions of the first six dyes have been replaced with the tetraphenylborate ion. Unlike the bases themselves, the quaternary salts are water soluble and have fluorescence characteristics independent of pH in the pH range 7–11. Both the fluorescence intensity and fluorescence lifetime of dyes 1–12 are reduced in the presence of aqueous halide ions allowing halide concentrations to be determined accurately at physiological levels. All the dyes have been characterised in terms of steady state fluorescence spectra and steady‐state Stern‐Volmer analysis.

Fluorescence lifetimes and linewidths of dye in photonic crystals

We have measured spectrally resolved fluorescence lifetimes of dye incorporated in high-quality photonic crystals, made of colloidal spheres. The emission spectrum shows a pronounced Bragg notch. In contrast, the fluorescence lifetime does not depend on the interaction between light and the photonic crystal. The results are explained with a simple model of an atom in a cavity. The effects of homogeneous and inhomogeneous broadening of the emission spectrum of dye inside photonic crystals are discussed.

Nanosecond time resolved emission spectroscopy of aminocoumarins in AOT reversed micelles

Time resolved emission spectroscopy of a water insoluble aminocoumarin derivative, BC I, in n-heptane–AOT–water reversed micelles is investigated using a nanosecond fluorescence spectrometer. The extent of the time-dependent Stokes shift is found to be smaller for W0=4 than for W0=10 and also for W0=40 (W0, molar ratio of water and AOT). A monoexponential decay of the dynamic Stokes shift correlation function with a time constant of 4.5 ns is observed at W0=4. At W0=10 the time-correlation function shows a bi-exponential decay with a fast component of ∽600 ps and another of 3.3 ns comparable to the fluorescence lifetime of the dye. The time correlation function at W0=40 shows an extremely slow component of the solvation time which is at least an order of magnitude larger than the fluorescence lifetime of the probe dye. In addition a faster component with a solvation time of 2.15 ns is also observed. The solvation time observed is likely due to the diffusion of the probe dye within the micellar interface or due to the reorganization of the water molecules bound to the polar head groups of AOT. Steady-state absorption and fluorescence, and time resolved fluorescence study of another aminocoumarin, C 480, give evidence of equilibrium between the distribution of the dye molecules between the interface and water pool. The time resolved shift of the emission spectra is more likely due to the diffusion of the probe between the interface and water pool rather than reorientation of the water molecules (solvent relaxation) in the core of the reversed micelles as it has been reported earlier.

Comparison of DODCI fluorescence depolarization in glycerol and ethylene glycol: Effect of orientational correlation on excitation transport

Time-correlated single-photon counting was used to obtain anisotropic fluorescence profiles for DODCI in ethylene glycol. Rotational diffusion of DODCI in this solvent was characterized at a concentration of ∼10−6 M, where minimal electronic excitation transport occurs during the dye fluorescence lifetime. The fluorescence depolarization due to excitation transport at higher concentrations was separated from that due to rotational diffusion; analysis of our data yields excellent agreement with current transport theories. The discrepancies observed between these theories and our earlier DODCI experiments in glycerol [J. Chem. Phys. 86, 2689 (1987)] appear to originate from orientational correlation of neighboring chromophores in that solvent; glycerol exhibits remarkable coherence in its total radial distribution function out to separations as large as 25 Å at temperatures between 250 and 350 K [Z. Naturforsch. Teil A 36, 1045 (1981)].

Fluorescence and energy transfer of dye-detergent systems in the premicellar region

The fluorescence lifetimes of dyes and also the energy transfer between dyes with closely located S 1 levels were studied in the presence of detergents. These dye-detergent systems can be considered as one of the model membrane systems of chloroplasts and show some peculiar features when the detergent has the opposite charge to that of the dye. The energy transfer efficiency between rhodamine 6G (Rh-6G) and pinacyanol (PC) in the presence of sodium lauryl sulphate (SLS) showed a distinct peak in the premicellar region, i.e. for [SLS] a little less than the critical micelle concentration. A long dimer-like lifetime was observed in the acridine orange (AO)-SLS system in the premicellar region. These findings and the absorption and fluorescence spectra revealed that the dye molecules are associated with dye-rich induced micelles which reduce the average distance (AO-AO or Rh-6G-PC) between dye molecules in the premicellar region.

Fluorescence and energy transfer of dye-detergent systems in the premicellar region

Abstract The fluorescence lifetimes of dyes and also the energy transfer between dyes with closely located S 1 levels were studied in the presence of detergents. These dye-detergent systems can be considered as one of the model membrane systems of chloroplasts and show some peculiar features when the detergent has the opposite charge to that of the dye. The energy transfer efficiency between rhodamine 6G (Rh-6G) and pinacyanol (PC) in the presence of sodium lauryl sulphate (SLS) showed a distinct peak in the premicellar region, i.e. for [SLS] a little less than the critical micelle concentration. A long dimer-like lifetime was observed in the acridine orange (AO)-SLS system in the premicellar region. These findings and the absorption and fluorescence spectra revealed that the dye molecules are associated with dye-rich induced micelles which reduce the average distance (AO-AO or Rh-6G-PC) between dye molecules in the premicellar region.