Biexponential photon antibunching: recombination kinetics within the Förster-cycle in DMSO

Abstract

Time-resolved experiments with pulsed-laser excitation are the standard approach to map the dynamic evolution of excited states, but ground-state kinetics remain hidden or require pump-dump-probe schemes. Here, we exploit the so-called photon antibunching, a purely quantum-optical effect related to single molecule detection to assess the rate constants for a chemical reaction in the electronic ground state. The measurement of the second-order correlation function g((2)), i.e. the evaluation of inter-photon arrival times, is applied to the reprotonation in a Förster-cycle. We find that the antibunching of three different photoacids in the aprotic solvent DMSO significantly differs from the behavior in water. The longer decay constant of the biexponential antibunching tl is linked to the bimolecular reprotonation kinetics of the fully separated ion-pair, independent of the acidic additives. The value of the corresponding bimolecular rate constant, kp = 4 × 10(9) M(-1) s(-1), indicates diffusion-controlled reprotonation. The analysis of tl also allows for the extraction of the separation yield of proton and the conjugated base after excitation and amounts to approximately 15%. The shorter time component ts is connected to the decay of the solvent-separated ion pair. The associated time constant for geminate reprotonation is approximately 3 ± 1 ns in agreement with independent tcspc experiments. These experiments verify that the transfer of quantum-optical experiments to problems in chemistry enables mechanistic conclusions which are hardly accessible by other methods.

Fluorescence-based characterization of non-fluorescent transient states of tryptophan – prospects for protein conformation and interaction studies

“…The observed behavior of Trp, with a photon antibunching relaxation time far longer than seen in single-molecule experiments on fluorophores 41 42 43 44 45 ( Eq. 4 ), is similar to that recently observed in single-molecule experiments on highly fluorescent photo-acids 51 52 . Rate parameters were fitted to the curves in Fig.…”

“…by replacing the frequency-tripled UV laser used for excitation in this work with a turn-key CW laser. Apart from the kinetics of triplet and photo-oxidized states, our TRAST measurements also revealed a pH- and buffer-dependent anti-bunching in the Trp fluorescence, previously only observed in specific, highly fluorescent photo-acids, requiring single-molecule or FCS measurements 51 52 . With its relatively much weaker fluorescence, anti-bunching in Trp fluorescence, or any transient state kinetics of Trp, is practically impossible to observe by FCS and single-molecule measurements.…”

Kinetic and spectroscopic responses of pH-sensitive nanoparticles: influence of the silica matrix

“…Faster uorescence uctuations, described by the second term in eqn (4), arise from the transient dark-state population. As no intensity-dependent dark-state population was noticed, which is in agreement with earlier experiments on this substance class, 64,68 the dark-state population exclusively results from the pH-dependent interconversion of the deprotonated dye (RO À form) and protonated dye (ROH form). The parameter k prot in eqn (4) describes the population of the dark-state ROH (protonation) and k deprot is the depopulation rate constant of the dark state (deprotonation).…”

“…The parameter k prot in eqn (4) describes the population of the dark-state ROH (protonation) and k deprot is the depopulation rate constant of the dark state (deprotonation). 64,68 However, eqn (4) is valid for molecular species like 5a/b; the preexponential factor k prot / k deprot is reduced if more than one uorophore per particle contributes to the uorescence. It should be noted that smaller particle sizes with lower absolute dye loading are benecial for this purpose.…”

Monomolecular pyrenol-derivatives as multi-emissive probes for orthogonal reactivities

“…Suchlike operation of 4 as a nontrivial Feynman gate appears promising in view of our own attempts to combine chemistry with quantum optics. 91,92 The described synthesis allows for a modification of pyrenol into a multi-wavelength probe for other analytes or macromolecules. Since the color of the fluorescence emission strongly relies on the substitution of the hydroxyl group ( position 6) by enabling or disabling deprotonation and to a minor extent on the opposite position ( position 1), more derivatives with orthogonal reactivities will be available.…”