Methodology for Discriminating between Competitive Photophysical Processes in Photoblinking: Application to the Fluorescence Blinking of Single Dye Molecules Adsorbed on TiO<sub>2</sub>

Mitsui, Masaaki; Unno, Aki; Mori, Kyosuke

doi:10.1246/cl.170127

Cited by 5 publications

(11 citation statements)

References 39 publications

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“…The blinking dynamics of EY on TiO 2 are characterized by short bursts of emission (i.e., on times < 100 ms) that are interspersed with longer off times (Figure c). Previous studies have shown that applying a simple threshold to quantify the emissive and non-emissive events is problematic. ,,− Therefore, blinking dynamics are analyzed using a CPD method that we adapted for binned data. − CPD analysis of the molecule in Figure c reveals 12 distinct intensity levels, including 38 on events and 37 off events, and an event frequency (υ event ), defined as the number of on and off events per second of 0.375 s –1 . For this molecule, on times ( t on ) ranging from 20 ms to 13.47 s and off times ( t off ) from 10 ms to 12.22 s are observed.…”

Section: Resultsmentioning

confidence: 99%

“…For example, the photophysical distributions of coumarin 343 and cresyl violet, , Atto647N, a Zn porphyrin, and a Ru(II) polypyridyl complex , on TiO 2 have been reported to follow power laws, consistent with a mechanism in which the rate constants for injection ( k inj ) and BET ( k BET ) vary due to an exponential distribution of activation energies to photoinduced electron transfer . Chen and Marcus also proposed a reaction-diffusion mechanism to explain the observation of power laws .…”

Section: Introductionmentioning

confidence: 88%

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Origin of Kinetic Dispersion in Eosin-Sensitized TiO₂: Insights from Single-Molecule Spectroscopy

et al. 2021

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By removing the effects of ensemble averaging and molecular aggregation, we untangle the factors that govern the dispersive electron transfer kinetics of eosin-sensitized TiO 2 , focusing on the impact of environmental heterogeneity versus injection from multiple excited states. The blinking dynamics of single eosin Y chromophores on nanocrystalline TiO 2 films are analyzed using a change point detection algorithm for binned data. Robust statistical analysis based on maximum likelihood estimation, Kolmogorov−Smirnov tests, and log likelihood ratio tests is used to determine the functional form that best fits the resulting on-and off-time distributions and to distinguish between mechanisms for dispersive electron transfer. Using this approach, we find that the on-and off-time distributions for eosin Y on TiO 2 are best fit to lognormal distributions corresponding to μ on = −0.64 ± 0.04, σ on = 1.52 ± 0.02, μ off = −0.23 ± 0.04, and σ off = 1.96 ± 0.03, respectively. Monte Carlo simulations based on the Albery model for dispersive electron transfer (i.e., where the median rate constant κ is modified by the exponential of a parameter, x, that is normally distributed, k = κ e −γx ) successfully reproduce this behavior using a median rate constant for injection and back electron transfer of ∼10 10 and ∼10 4 s −1 , respectively, and a corresponding energetic dispersion, γ, of ∼200−350 meV. To examine how injection from both the singlet and triplet excited states contributes to this dispersion, we studied two rhodamine sensitizers, R123 and 5ROX, that inject only from their singlet excited state. Surprisingly, when access to the T 1 state is minimized in going from EY to R123 and 5ROX, kinetic dispersion actually increases. Collectively, these observations support the interpretation that static and dynamic inhomogeneities at the EY−TiO 2 interface govern kinetic dispersion, with dynamic fluctuations in binding configuration and/or vibrational motion playing a decisive role.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 88%

Origin of Kinetic Dispersion in Eosin-Sensitized TiO₂: Insights from Single-Molecule Spectroscopy

et al. 2021

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“…Recently, Mitsui and co-workers developed a "scanning" MLE/KS method, where the onset time (t min ) of log-normal behavior is progressively changed to determine if the data contains contributions from other functions. 56 By calculating the p-value as a function of t min , they demonstrated the off-time probability distribution of Atto 647N dyes on TiO 2 is welldescribed using a combination of exponential, power-law, and log-normal functions. An alternative approach, described by Clauset and co-workers, 27 uses the combined MLE/KS method to determine the best t min such that the data are fit only where the log-normal distribution is operative.…”

Section: ■ Discussionmentioning

confidence: 99%

“…Recently, Mitsui and co-workers developed a “scanning” MLE/KS method, where the onset time ( t min ) of log-normal behavior is progressively changed to determine if the data contains contributions from other functions . By calculating the p -value as a function of t min , they demonstrated the off-time probability distribution of Atto 647N dyes on TiO 2 is well-described using a combination of exponential, power-law, and log-normal functions.…”

Section: Discussionmentioning

confidence: 99%

Unraveling the Excited-State Dynamics of Eosin Y Photosensitizers Using Single-Molecule Spectroscopy

2019

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The intersystem crossing and dispersive electron-transfer dynamics of eosin Y (EY) photosensitizers are probed using single-molecule microscopy. The blinking dynamics of EY on glass are quantified by constructing cumulative distribution functions of emissive (“on”) and nonemissive (“off”) events. Maximum likelihood estimation (MLE) and goodness-of-fit tests based on the Kolmogorov–Smirnov (KS) statistic are used to establish the best fit to the blinking data and differentiate among competitive photophysical processes. The on-time probability distributions for EY in N2 and air are power-law distributed after ∼1 s, with fit parameters that are significantly modified upon exposure to oxygen. By extending the statistically principled MLE/KS approach to include an onset time for log-normal behavior, we demonstrate that the off-time distribution for EY in N2 is best fit to a combination of exponential and log-normal functions. The corresponding distribution for EY in air is best fit to a log-normal function alone. Furthermore, power law and log-normal distributions are observed for an individual molecule in air, consistent with dynamic fluctuations in the rate constant for dark-state population and depopulation. These observations support the interpretation that dispersive electron transfer (i.e., the Albery model) from the first excited singlet state (S1) of EY to trap states on glass is predominately responsible for blinking in oxic conditions. In anoxic environment, both triplet-state blinking and dispersive electron transfer from S1 and the excited triplet state (T1) contribute to the excited-state dynamics of EY.

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“…Single-molecule fluorescence spectroscopy (SMFS) is widely employed to obtain statistical information (e.g., histograms, correlations, and time evolution) on the photophysical parameters of photoluminescent chromophores under various solid environments. − Therefore, SMFS is an indubitably effective and emerging technique for revealing the photophysical behaviors of multipolar chromophores in rigid environments.…”

Section: Introductionmentioning

confidence: 99%

Impacts of Environmental Rigidity on Photophysical Characteristics and Behaviors of a Quadrupolar Chromophore Revealed by Single-Molecule Fluorescence Spectroscopic Study

et al. 2018

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Multipolar chromophores (e.g., quadrupolar and octupolar molecules) have excellent two-photon absorption properties and exhibit characteristic excited-state relaxation behaviors that involve structural symmetry breaking. Environmental rigidity could provide an appreciable impact on such conformational rearrangement in the excited state; however, details of its effect remain unclear. Herein, we undertake an ensemble and single-molecule spectroscopic investigation into the effects of environmental rigidity on the photophysical characteristics and behaviors of a newly synthesized D−π−A−π−D (donor−π−acceptor−π−donor) quadrupolar chromophore, QC, and its π−A−π analogue, AC, in various solutions and polymers. The fluorescence emission of QC in nonpolar solvents takes place in the symmetric quadrupolar state [D δ+ −π−A δ− −π−D δ+ ]*, whereas the significant fluorescence quenching is observed with increasing solvent polarity, suggesting the gradual stabilization of the nonemissive symmetry-broken dipolar state [D δ+ −π−A δ− ]*−π−D or D−π− [A δ− −π−D δ+ ]* in more polar solvents. However, because of a lack of environmental rearrangement, this dipolar state is not effectively stabilized in a polar polymer matrix. Single-molecule fluorescence spectroscopy was used to explore how environmental rigidity affects the photophysical behaviors of QC and AC. In a rubbery poly(methyl acrylate) (PMA) film, the QC and AC single molecules exhibited fluorescence properties similar to those in nonpolar solutions. Remarkably, the average fluorescence lifetime of QC in the glassy PMA film was longer than that in the rubbery film. Moreover, the heterogeneity of single-molecule fluorescence lifetimes increased considerably, although such variation was not observed for the nonquadrupolar chromophore AC. Experimental and theoretical considerations suggest that fluorescence emission of QC embedded in the rubbery polymer most probably occurs from the symmetric quadrupolar state formed through planarization, whereas such conformational relaxation is suppressed in the glassy polymer because the physical constraint and various degree-of-twist conformations of QC emit fluorescence photons. Overall, this study reveals that environmental rigidity appreciably alters the photophysical characteristics and behaviors of quadrupolar chromophores.

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Methodology for Discriminating between Competitive Photophysical Processes in Photoblinking: Application to the Fluorescence Blinking of Single Dye Molecules Adsorbed on TiO₂

Cited by 5 publications

References 39 publications

Origin of Kinetic Dispersion in Eosin-Sensitized TiO₂: Insights from Single-Molecule Spectroscopy

Origin of Kinetic Dispersion in Eosin-Sensitized TiO₂: Insights from Single-Molecule Spectroscopy

Unraveling the Excited-State Dynamics of Eosin Y Photosensitizers Using Single-Molecule Spectroscopy

Impacts of Environmental Rigidity on Photophysical Characteristics and Behaviors of a Quadrupolar Chromophore Revealed by Single-Molecule Fluorescence Spectroscopic Study

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Methodology for Discriminating between Competitive Photophysical Processes in Photoblinking: Application to the Fluorescence Blinking of Single Dye Molecules Adsorbed on TiO2

Cited by 5 publications

References 39 publications

Origin of Kinetic Dispersion in Eosin-Sensitized TiO2: Insights from Single-Molecule Spectroscopy

Origin of Kinetic Dispersion in Eosin-Sensitized TiO2: Insights from Single-Molecule Spectroscopy

Unraveling the Excited-State Dynamics of Eosin Y Photosensitizers Using Single-Molecule Spectroscopy

Impacts of Environmental Rigidity on Photophysical Characteristics and Behaviors of a Quadrupolar Chromophore Revealed by Single-Molecule Fluorescence Spectroscopic Study

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Product

Resources

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Methodology for Discriminating between Competitive Photophysical Processes in Photoblinking: Application to the Fluorescence Blinking of Single Dye Molecules Adsorbed on TiO₂

Origin of Kinetic Dispersion in Eosin-Sensitized TiO₂: Insights from Single-Molecule Spectroscopy

Origin of Kinetic Dispersion in Eosin-Sensitized TiO₂: Insights from Single-Molecule Spectroscopy