On-off-on Control of Molecular Inversion Symmetry via Multi-stage Protonation: Elucidating Vibronic Laporte Rule

Abstract
The Laporte rule dictates that one- and two-photon absorption spectra of inversion-symmetric molecules should display alternatively forbidden electronic transitions; however, for organic fluorophores, drawing clear distinction between the symmetric- and non-inversion symmetric two-photon spectra is often obscured due to prevalent vibronic interactions. We take advantage of consecutive single- and double-protonation to break and then reconstitute inversion symmetry in a nominally symmetric diketopyrrolopyrrole, causing large changes in two-photon absorption. By performing detailed one- and two-photon titration experiments, with supporting quantum-chemical model calculations, we explain how certain low-frequency vibrational modes may lead to apparent deviations from the strict Laporte rule. As a result, the system may be indeed considered as an on-off-on inversion symmetry switch, opening new avenues for two-photon sensing applications.
Description
Keywords
Citation
Stark, C..W., Rammo, M., Trummal, A., Uudsemaa, M., Pahapill, J., Sildoja, M., Tshepelevitsh, S., Leito, I., Young, D..C., Szymański, B., Vakuliuk, O., Gryko, D..T. and Rebane, A. (2022), On-off-on Control of Molecular Inversion Symmetry via Multi-stage Protonation: Elucidating Vibronic Laporte Rule. Angew. Chem. Int. Ed.. Accepted Author Manuscript. https://doi.org/10.1002/anie.202212581
Belongs to collection