Non-typical fluorescence studies of excited and ground state proton and hydrogen transfer

Abstract

Fluorescence studies of tautomerization have been carried out for various systems that exhibit single and double proton or hydrogen translocation in various environments, such as liquid and solid condensed phases, ultracold supersonic jets, and finally, polymer matrices with single emitters. We focus on less explored areas of application of fluorescence for tautomerization studies, using porphycene, a porphyrin isomer, as an example. Fluorescence anisotropy techniques allow investigations of self-exchange reactions, where the reactant and product are formally identical. Excitation with polarized light makes it possible to monitor tautomerization in single molecules and to detect their three-dimensional orientation. Analysis of fluorescence from single vibronic levels of jet-isolated porphycene not only demonstrates coherent tunneling of two internal protons, but also indicates that the process is vibrational mode-specific. Next, we present bifunctional proton donor-acceptor systems, molecules that are able, depending on the environment, to undergo excited state single intramolecular or double intermolecular proton transfer. For molecules that have donor and acceptor groups located in separate moieties linked by a single bond, excited state tautomerization can be coupled to mutual twisting of the two subunits.

Proton-Transfer-Induced Fluorescence in Self-Assembled Short Peptides

“…Secondly, Hydrogen bonds enable proton transfer without barrier crossing, along the Hydrogen bond, resulting in a modified geometry with lower energy in the excited state. Such an effect of proton transfer induced fluorescence was also demonstrated in other molecular systems [26,38]. Our analysis also shows that the mechanism of proton transfer is highly dependent on the formation of specific Hydrogen bonds between the monomers.…”

“…Such an effect of proton-transfer-induced fluorescence was also demonstrated in other molecular systems. , Our analysis also shows that the mechanism of proton transfer is highly dependent on the formation of specific HBs between the monomers. Although we demonstrated this phenomenon with a dipeptide that possesses phenyl side groups, the mechanism is clearly dependent on the HBs and not on the aromatic nature of the side groups.…”

Porphycene Protonation: A Fast and Reversible Reaction Enabling Optical Transduction for Acid Sensing

“…The small values of both S M and Stokes shift indicate the great rigidity of the porphycene core and the overall small difference in the equilibrium position of the S 0 and S 1 potential curves. At 77 K (panel c ), in a frozen glassy matrix of 2‐MeTHF, both the emission and the excitation spectra undergo significant line narrowing with the appearance of rich vibronic structure in the region of the L band absorption which is reflected in the emission vibrational breathing modes [25,26] . At high energy, the Soret band resolves in two distinct peaks.…”

“…At 77 K (panel c), in a frozen glassy matrix of 2-MeTHF, both the emission and the excitation spectra undergo significant line narrowing with the appearance of rich vibronic structure in the region of the L band absorption which is reflected in the emission vibrational breathing modes. [25,26] At high energy, the Soret band resolves in two distinct peaks. The emission lifetime at 77 K increases to 12.3 ns and the strong 0-0 overlap is again an evidence of the molecular rigidity.…”

Bioinspired Amyloid Nanodots with Visible Fluorescence

“…The latter concept is illustrated in Figure d with a possible Frank–Condon diagram that involves proton transfer in higher excited states and can lead to multicolor excitation‐dependent FL. The possibility of excited state proton transfer involvement in FL can be observed in a wide range of systems, including GFP. Quantum molecular modeling (DFT and TDDFT simulations) showed that proton transfer can induce gap reduction in several self‐assembled peptide structures …”