Photon Antibunching in a Cyclic Chemical Reaction Scheme

Abstract

The direct observation of chemical reactions on the single-molecule level is an ultimate goal in single-molecule chemistry, which also includes kinetic analyses. To analyze the lifetime of reaction intermediates, very sophisticated excitation schemes are often required. Here we focus on the kinetic analysis of the ground-state proton transfer within the photocycle of a photoacid. In detail, we demonstrate the determination of the bimolecular rate constant of this process with nanosecond resolution. The procedure relies on the exploration of a purely quantum-optical effect, namely, photon antibunching, and thus on evaluating interphoton arrival times to extract the reaction rate constant.

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.…”

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.…”

Single-molecule photoredox catalysis

“…On longer timescales, the opposite effect occurs: the fluorescent molecule undergoes quantum jumps between bright and dark states, for example between the singlet and the triplet manifolds of the excited state, leading to bunching of photons in time 43. This cycling between emissive and non-emissive states of the fluorophore provides crucial insight into the molecular quantum jumps responsible for the photosynthetic reaction 44…”