https://doi.org/10.1140/epjd/s10053-023-00744-z
Regular Article – Molecular Physics and Chemical Physics
Excited-state dynamics of deuterated indigo
1
Department of Chemistry and Biochemistry, University of California Santa Barbara, 93106-9510, Santa Barbara, CA, USA
2
Institute of Physics, Polish Academy of Sciences, al. Lotnikow 32/46, 02-668, Warsaw, Poland
Received:
4
May
2023
Accepted:
12
August
2023
Published online:
4
September
2023
Indigo, a rich blue dye, is an incredibly photostable molecule that has survived in ancient art for centuries. It is also unique in that it can undergo both an excited-state hydrogen and proton transfer on the picosecond timescale followed by a ground-state back transfer. Previously, we performed gas phase excited-state lifetime studies on indigo to study these processes in a solvent-free environment, combined with excited-state calculations. We found two decay pathways, a fast sub-nanosecond decay and a slow decay on the order of 10 ns. Calculations of the excited-state potential energy surface found that both hydrogen and proton transfer are nearly isoenergetic separated by a 0.1 eV barrier. To further elucidate these dynamics, we now report a study with deuterated indigo, using resonance-enhanced multi-photon ionization and pump-probe spectroscopy with mass spectrometric isotopomer selection. From new calculations of the excited-state potential energy surface, we find sequential double-proton or hydrogen transfer, whereby the trajectory to the second transfer passes a second barrier and then encounters a conical intersection that leads back to the ground state. We find that deuteration only increases the excited-state lifetimes of the fast decay channel, suggesting tunneling through the first barrier, while the slower channel is not affected and may involve a different intermediate state.
© The Author(s) 2023
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