Analysis Of Fluorescence Decay Curves Research Articles

Time-resolved fluorescence spectroscopy for studying stepwise excited-state intramolecular double proton transfer

Nowadays, single excited-state intramolecular proton transfer (ESIPT) is well studied and widely reported. However, excited-state multiple intramolecular proton transfer has not been thoroughly researched until the past decade. And now there is an increasing scientific interest not only in single but also in multiple ESIPT processes occurred in various molecules, because it offers great opportunities to apply such compounds in chemical sensors, molecular switches, NIR emitting devices and liquid crystals with high fluorescence. A stepwise excited-state intramolecular double proton transfer (ESIDPT) is among such multiple ESIPT processes. Similar to the single ESIPT, stepwise ESIDPT also occurs via an intramolecular hydrogen bonding way. But in the stepwise ESIDPT, two proton transfers occur sequentially in a molecule, because there is only one proton transfer site in the initial molecular structure. Then, after the first ESIPT, an additional proton transfer site appears, and the second proton transfer will occur.In this work, an emission of stepwise ESIDPT-active molecules was studied from the point of view of a time-resolved fluorescence spectroscopy. The theoretical model for emission decay was discussed on the basis of a six states model. This model consists of three pairs of ground and excited states for normal molecular form and two tautomers. It leads to three-exponential equations for emission decay functions. It was shown that a thorough analysis of fluorescence decay curves allows to estimate the total decay rate constants for each excited molecular form. The proposed model has been validated for a numerically simulated case. The experimental data have also been discussed from the point of view of the proposed model.

Ba2Zn2La4O10:Sm3+: A novel orange–red emitting nanophosphor with high color purity for WLEDs applications

Ba2Zn2La4(1−x)O10:4xSm3+ (0.5–6 mol%) nanophosphor series synthesized successfully via solution combustion approach were crystallized into tetragonal lattice (I4/mcm (140) space group symmetry). The qualitative and quantitative phase information was obtained by performing Rietveld refinement technique. Morphological studies were carried out via scanning and transmission electron microscopy (SEM & TEM) observations. The energy-gap values for Ba2Zn2La4O10(5.58 eV) and Ba2Zn2La3.88Sm0.12O10(5.42 eV) powder samples were determined from diffuse reflectance (DR) studies. The near ultra-violet (NUV) excitation (λex = 410 nm) of Sm3+-doped nanophosphors revealed strong reddish-orange (603 nm) emission accredited to 4G5/2→6H7/2 (most prominent) transition. The Blasse’s relation provided critical distance (16.39 A) for energy transfer process amid adjacent activator centres and shortlisted the actual interaction type (dipole–quadrupole) behind concentration quenching behaviour. Non-radiative relaxation rate (78.7701 s− 1), radiative lifetime (1.61 ms) and quantum efficiency (89%) of 4G5/2 emitting state were obtained by detailed analysis of fluorescence decay curves of Ba2Zn2La4(1−x)O10:4xSm3+ series. Furthermore, the CIE chromaticity diagram provides strong reddish-orange luminescence in visible region, which displays the auspicious applications of Ba2Zn2La4O10:Sm3+ nanophosphor in NUV-based white LEDs.

Light-Enhanced Fluorescence of Multi-Level Cavitands Possessing Pyridazine Upper rim.

Completely different fluorescence behaviour of cavitands based on a same calix[4]resorcinarene compound was observed. While the fluorescence intensity of the parent compound, tetramethyl-cavitand (1) slowly faded as a result of UV-light exposure, the emission of the three-level cavitand with pyridazine moieties at the upper rim (5a) was enhanced by the excitation in the UV-region. The structure of fluorescence emission (characterized by excitation-emission matrices) and the absorption of 5a remained unaltered. The analysis of fluorescence decay curves reveals the presence of two separated components assigned to two individual emitting species. The measured significant increase of the average lifetime and quantum yield is the consequence of the UV-light induced transition between the different states of 5a. These observations can be explained by the structural difference between 5a and 1. As a counterpart of the naked cavitand (1) with methyl substituents at the upper rim only, 5a has three additional moieties benzene, triazole and pyridazine levels. Computational studies proved the existence of two conformational isomers of 5a. Upon ultraviolet light excitation a "dark" to "light" conformational transition occurs between the two isomers. This hypothesis was confirmed by anisotropy decay measurements.

Diffusion-facilitated direct determination of intrinsic parameters for rapid photoinduced bimolecular electron-transfer reactions in nonpolar solvents.

Bimolecular fluorescence-quenching reactions involving electron-transfer between electronically excited 5,10,15,20-tetraphenyl-21H,23H-porphine (TPP*) and 1,4-benzoquinone (BQ) or 1,4-naphthoquinone (NQ) were investigated using a set of alkane solvents that enabled the rapid reaction kinetics to be probed over a wide viscosity range, while minimizing changes in other relevant solvent parameters. Relative diffusion coefficients and reaction distances were recovered directly from analysis of fluorescence decay curves measured on a nanosecond time scale. The electron transfer from TPP* to BQ requires reactant contact, consistent with tightly associated exciplex formation in these nonpolar solvents. In contrast, electron transfer from TPP* to NQ displays a clear distance dependence, indicative of reaction via a much looser noncontact exciplex. This difference is attributed to the greater steric hindrance associated with contact between the TPP*/NQ pair. The diffusion coefficients recovered from fluorescence decay curve analysis are markedly smaller than the corresponding measured bulk relative diffusion coefficients. Classical hydrodynamics theory was found to provide a satisfactory resolution of this apparent discrepancy. The calculated hydrodynamic radii of TPP and NQ correlate very well with the van der Waals values. The hydrodynamic radius obtained for BQ is a factor of 6 times smaller than the van der Waals value, indicative of a possible tight cofacial geometry in the (TPP(+)/BQ(-))* exciplex. The present work demonstrates the utility of a straightforward methodology, based on widely available instrumentation and data analysis, that is broadly applicable for direct determination of kinetic parameter values for a wide variety of rapid bimolecular fluorescence quenching reactions in fluid solution.

Plasmon-enhanced fluorescence in heterochlorophyllous peridinin-chlorophyll-protein photosynthetic complex

We study the fluorescence properties of peridinin-chlorophyll-protein light-harvesting complex reconstituted with both chlorophyll a and chlorophyll b coupled to spherical gold nanoparticles. Since there is a bidirectional energy transfer between the chlorophylls, the impact of plasmon excitations upon the energy transfer dynamics can be studied in such a hybrid nanostructure. The results show that the emission of both chlorophyll a and chlorophyll b in a reconstituted PCP is strongly enhanced when the light-harvesting complexes are separated from the metallic nanoparticles by a 12-nm-thick SiO2 layer, the average enhancement reaches a factor of 8. The analysis of fluorescence decay curves indicates that the energy transfer between chlorophyll a and chlorophyll b is also influenced by plasmon excitations in gold nanoparticles.

Non‐invasive evaluation of dermal elastosis by in vivo multiphoton tomography with autofluorescence lifetime measurements

The non-invasive differentiation of dermal elastic fibres from solar elastosis in vivo is of great interest in dermatologic research, especially for efficacy testing of anti-ageing products. To date, no studies on multiphoton excited fluorescence lifetime characteristics of human elastic fibres and solar elastosis are reported. The goal of the present work was the identification of differential criteria for elastic fibres and solar elastosis by the analysis of fluorescence decay curves acquired by time-correlated single photon counting in vivo multiphoton tomography. For this purpose, fluorescence lifetime measurements (FLIM) were performed with 47 volunteers of different age groups at sun-protected and sun-exposed localizations. Bi-exponential curve fitting was applied to the FLIM data, and characteristic differences between age groups and localizations were found in both relevant fit parameters describing the decay slope. The FLIM analyses have shown that dermal autofluorescence has different lifetimes depending on age and in part on localization.

Fluorescence lifetime spectroscopy and imaging of nano-engineered glucose sensor microcapsules based on glucose/galactose-binding protein

We aimed to develop microsensors for eventual glucose monitoring in diabetes, based on fluorescence lifetime changes in glucose/galactose-binding protein (GBP) labelled with the environmentally sensitive fluorophore dye, badan. A mutant of GBP was labelled with badan near the binding site, the protein adsorbed to microparticles of CaCO 3 as templates and encapsulated in alternating nano-layers of poly- l-lysine and heparin. We used fluorescence lifetime imaging (FLIM) with two-photon excitation and time-correlated single-photon counting to visualize the lifetime changes in the capsules. Addition of glucose increased the mean lifetime of GBP-badan by a maximum of ∼2 ns. Analysis of fluorescence decay curves was consistent with two GBP states, a short-lifetime component (∼0.8 ns), likely representing the open form of the protein with no bound glucose, and a long-lifetime component (∼3.1 ns) representing the closed form with bound glucose and where the lobes of GBP have closed round the dye creating a more hydrophobic environment. FLIM demonstrated that increasing glucose increased the fractional proportion of the long-lifetime component. We conclude that fluorescence lifetime-based glucose sensing using GBP encapsulated with nano-engineered layer-by-layer films is a glucose monitoring technology suitable for development in diabetes management.

Energy transfer processes in the ytterbium doped NdPO4 stoichiometric crystal

We report on crystal growth and fluorescence characterization of Yb3+ doped NdPO4 single crystals. From the analysis of fluorescence decay curves, the temperature dependence of Nd3+ → Yb3+ and Nd3+ ← Yb3+ energy transfer processes has been obtained. We have found that the dominant process is strongly temperature dependent, this leading to a temperature induced luminescence switching from Yb3+ to Nd3+ ions.

Temperature dependence of Nd3+↔Yb3+ energy transfer in the YAl3(BO3)4 nonlinear laser crystal

The temperature dependence of the Nd3+→Yb3+ energy-transfer rate in the YAl3(BO3)4 nonlinear laser crystal has been investigated from the analysis of fluorescence decay curves recorded in the 10–600 K range. Three different regimes, independent on the dopant concentration, have been observed in the thermal behavior of the Nd3+→Yb3+ energy-transfer rate. By comparing experimental results with theoretical predictions based on the Dexter model [J. Chem. Phys. 21, 836 (1953)], the origin of these different regimes has been explained. In addition, the influence of temperature and of both Nd3+ and Yb3+ concentrations on the Nd3+←Yb3+ energy back-transfer rate has been also investigated, concluding that it is a migration-assisted energy-transfer process. Finally, the populations of both Nd3+ and Yb3+ metastable states achieved after continuous-wave Nd3+ excitation have been calculated and measured and results have been explained in terms of the thermal behavior of both forward- and back-transfer rates.

Determination of stoichiometry and equilibrium constants of complexes of tyrosine with cyclodextrins by time-resolved fluorescence spectroscopy and global analysis of fluorescence decays

Time-resolved fluorescence spectroscopy and global analysis of fluorescence decay times were applied to determine stoichiometry and equilibrium constants of complexes of tyrosine with α-, β- and γ-cyclodextrins (CDs). This study reveals from Global analysis of fluorescence decay curves of tyrosine with CDs in water the presence of only two fluorescence life-times of tyrosine: 3.35±0.10 ns for free tyrosine and 4.3±0.3 ns for the tyrosine–CD complex. The formation constants of tyrosine–CD complexes were determined from the pre-exponential factors as well as the fractional intensities and average fluorescence life-times. The cavity size of CD influenced the equilibrium constant but had no influence on the fluorescence life-time of the tyrosine–CD complex.

Energy Transfer in the Restricted Geometry of Lamellar Block Copolymer Interfaces

We carried out simulations of energy transfer kinetics for lamellar block copolymer systems in which donor and acceptor dyes were attached to the block junctions. We considered blocks of homopolymers that were sufficiently immiscible and of sufficiently high molecular weight to employ the Helfand-Tagami distribution of block junctions. The morphology of such block copolymers has been frequently discussed in terms of an apparent dimension parameter, which is recovered from the analysis of fluorescence decay curves, using the Klafter-Blumen (KB) formalism. Here, we investigate how such apparent dimensions are influenced by the interface thickness between the two blocks (which is dependent on the Flory-Huggins parameter of the system). We also probe the dependence of this apparent dimension on the concentration of the dyes in labeled samples. This kind of dependence has been experimentally observed but never explained, perhaps because of the approximations inherent in using the KB model to analyze fluorescent decay curves for block copolymer systems. We have found that apparent dimensions approach three for reasonably broad interfaces, but decrease to near two for very narrow interfaces, in accordance with asymptotic formulas that we propose for strongly segregated, lamellar block copolymer melts. Global analysis of the decay curves, as well as weighted linear regression of the parameters obtained from individual analyses of the decays, suggest linear relationships between the apparent dimensions from KB analyses and acceptor concentrations. We discuss the dependence

Excitation energy transfer of porphyrin in polymer thin films by time-resolved scanning near-field optical microspectroscopy.

Thin films of water-soluble free-base porphyrin, 5,10,15,20-tetraphenyl-21H, 23H-porphinetetrasulphonic acid (TPPS) mixed with poly(diallyldimethyl ammonium chloride) (PDDA) have been prepared by a spin-coating method, in which the monomeric species were observed in the spin-coat film, whereas dimer was formed in the cast film prepared from TPPS/PDDA solution. Mesoscopic structures and dynamics of excitation energy migration and trapping of TPPS/PDDA spin-coat film have been analysed by time-resolved scanning near-field optical microspectroscopy (SNOM) and atomic force microscope. The observed film structure can be classified roughly into two parts: one is a large, flocculated polymer part, and the other is a smooth part widely spread around the flocculated polymers. In the smooth part, the observed spindle-like structure and circular hills and dips are essentially due to PDDA. The ellipsoidal small structures with approximately 2 microm length and < 1 microm width in the flocculated polymer part show non-exponential fluorescence decays. The non-exponential dynamics originates from the excitation energy migration among TPPS monomers and energy trapping to dimers. From the analysis of fluorescence decay curves based on the equation developed by Klafter and Blumen, the spectral dimension has been estimated to be approximately 1.46 for ellipsoidal structures. These results indicate that the distribution of the chromophore is inhomogeneous and a fractal-like structure exists even in the small domains determined by the resolution of the SNOM tip.

Direct determination of kinetic parameters for diffusion-influenced reactions in solution by analysis of fluorescence decay curves

Fluorescence decay curves were synthesized using the Smoluchowski-Collins-Kimball (SCK) model for diffusion-influenced bimolecular reactions so as to simulate measurements using the technique of time-correlated single photon counting (TCSPC). The experimental conditions required for successful recovery of the parameters used to generate these decay curves were assessed by direct analysis using the decay function associated with the SCK model, where the term "direct analysis" refers to analysis in which all of the fundamental parameters associated with the SCK model are permitted to vary freely. Analysis of decay curves synthesized using an instrument response function measured using a flash-lamp TCSPC system and having a full-width at halfmaximum (fwhm) of approximately 2.8 ns was unsuccessful for the values of the parameters associated with the SCK model that were used in this work. However, analysis of these synthesized fluorescence decay curves using the long-time approximation to the SCK model was found to be valid. The results of analysis of fluorescence decay curves synthesized using a 37-ps fwhm instrument response function indicate that the long-time approximation becomes a poor description of the kinetics of diffusion on the time scale associated with these decay curves. Furthermore, direct analysis using the function associated with the SCK model of the synthesized fluorescence decay curves convoluted with this response function and containing 5.0× 10(4) or 1.0 × 10(5) counts in the channel of maximum intensity resulted in the recovery of parameter values that are in very good agreement with those used to generate these decay curves. The results obtained using the simple methodology developed in this work demonstrate for the first time that direct analysis of fluorescence decay curves measured using TCSPC according to the decay function derived from the SCK model can yield reliable estimates for values of the relevant parameters under suitable experimental conditions.

Parameter recovery and discrimination between different types of fluorescence decays obtained for dipole-dipole energy transfer in low-dimensional systems

In several low-dimensional systems deviations from the stretched exponential fluorescence decays of the donor in the presence of Förster-type energy transfer were attributed to microheterogeneity of the samples or to a self-similar distribution of acceptors. In the present contribution the ability of single curve and global analysis of fluorescence decay curves, obtained by means of time-correlated single photon counting experiments, to discriminate between models characteristics for microheterogeneity and a self-similar distribution of acceptors was investigated. Furthermore the accuracy of the recovery of the system parameters is discussed.

Methods of analysis of fluorescence decay curves in pulsed fluorometry (review)

Methods of analysis of fluorescence decay curves in pulsed fluorometry (review)

Measurements of Fluorescence Heterogeneity in Human Teeth Using Polarization Microfluorometry

Human teeth fluoresce as a result of illumination by UV-light (λmax = 450 nm). The spectral, anisotropic, and temporal heterogeneities of a tooth's fluorescence have been investigated with respect to tooth structure. A polarization microfluorometer and a time-resolved fluorometer were employed. The fluorescence intensity of the dentin increases with tooth age. On the basis of the fluorometric investigations, it appears that a complex of cross-linked collagen with hydroxyapatite is a possible fluorescing compound within the tooth tissue. Observed fluorescence anisotropy in the tooth tissue suggests heterogeneous structure of the fluorescing compound. Anisotropy distribution shows characteristic profiles which are independent of age and sex, and of type of tooth. Analysis of fluorescence decay curves suggests that such profiles are due to the characteristic arrangement of the fluorophore electric dipole, which in turn relates to tissue construction.

Simultaneous analysis of fluorescence decay curves for the one-step determination of the mean aggregation number of aqueous micelles

The practical applicability of the global non-linear least-squares analysis of multiple fluorescence decay curves is examined using real micellar decay data. Fluorescence decays of 1-methylpyrene quenched by the “immobile” quencher N-tetradecylpyridinium chloride in sodium dodecyl sulphate (SDS) micelles were measured using the single-photon timing method with reference convolution. Decays with 10 3 and 10 4 peak counts were analyzed individually and simultaneously. The globally determined mean aggregation number ( N agg = 69) of SDS is in excellent agreement with literature values determined from single curve analyses.

Global analysis of fluorescence decay: applications to some unusual experimental and theoretical studies.

AbstractThe methodology for the simultaneous analysis of fluorescence decay curves is shown to create the possibility for some new types of fluorescence decay experiments. These new experiments include the use of the T‐format in anisotropy experiments without the need to match the timing characteristics of photomultiplier tubes. Decay surfaces obtained at multiple timing calibrations can be analyzed simultaneously to resolve widely differing decay rates. Methodologies are described for the discrimination of associative from nonassociative behavior for multiexponential anisotropy decay. A systems theory approach to the analysis of excited state reactions is described.

Excimer formation of N-(1-pyrenesulfonyl)-dipalmitoyl-L-alpha-phosphatidylethanolamine at the lipid-water interface of fat cell plasma membranes.

Abstract— The mechanism of excimer formation of N‐(l‐pyrenesulfonyl)‐dipalmitoyl‐L‐α‐phosphatidylethanolamine incorporated into fat cell plasma membranes was studied by means of steady‐state and pulse fluorometry. It was found that the pyrenesulfonyl group at the lipid‐water interface of the membrane formed an appreciable amount of ground‐state dimers and that the excimer of the pyrenesulfonyl group was formed through two different processes: (i) the collisional interaction of an excited monomer with a ground‐state monomer, and (ii) the direct excitation of a ground‐state dimer (approximate ratio of the two processes, 1:1). Analysis of fluorescence decay curves revealed that the detailed mechanism of excimer formation by process (i) is essentially similar to the mechanism established for the reaction in organic solvents but not to that in a highly viscous medium such as the hydrocarbon core of the membrane.

Quencing of perylene fluorescence by Ag + ions via exciplex formation

The fluorescence of perylene in alcoholic solution is dynamically quenched by AgClO 4 resulting in a new emission band with its maximum around 480 nm. Analysis of fluorescence decay curves at various emission wavelengths proves the formation of a perylene/Aa + ion exciplex in the quenching reaction.