Excited state structure correlates with efficient photoconversion in unidirectional motors

Palas Roy, Andy S. Sardjan, Arjen Cnossen, Wesley R. Browne, Ben L. Feringa, Stephen R. Meech

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)
18 Downloads (Pure)


The design of unidirectional photomolecular motors demands a critical understanding of an ultrafast photochemical isomerization. An intermediate dark excited state mediates the reaction via a conical intersection (CI) with the ground state, but a correlation between molecular structure and photoisomerization efficiency has remained elusive. Here femtosecond stimulated Raman spectroscopy captures vibrational spectra of the dark state in a set of molecular motors bearing different substituents. A direct correlation between isomerization quantum yield, dark state lifetime, and excited state vibrational spectrum is found. Electron withdrawing substituents lead to activity in lower frequency modes, which we correlate with a pyramidalization distortion at the ethylenic axle occurring within 100 fs. This structure is not formed with an electron donating substituent, where the axle retains double bond character. Further structural reorganization is observed and assigned to excited state reorganization and charge redistribution on the sub-picosecond time scale. The correlation of the dark state structure with photoconversion performance suggests guidelines for developing new more efficient motor derivatives.

Original languageEnglish
Pages (from-to)3367-3372
Number of pages6
JournalThe Journal of Physical Chemistry Letters
Issue number13
Early online date30 Mar 2021
Publication statusPublished - 8 Apr 2021

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