E to Z Photoisomerization of Phytochrome Cph1ΔExceeds the Born-Oppenheimer Adiabatic Limit

Laurie A. Bizimana, Camille A. Farfan, Johanna Brazard, Daniel B. Turner

Research output: Contribution to journalArticlepeer-review


The Born-Oppenheimer adiabatic limit applies broadly in chemistry because most reactions occur on the ground electronic state. Photochemical reactions involve two or more electronic states and need not be subject to this adiabatic limit. The spectroscopic signatures of nonadiabatic processes are subtle, and therefore, experimental investigations have been limited to the few systems dominated by single photochemical outcomes. Systems with branched excited-state pathways have been neglected, despite their potential to reveal insights into photochemical reactivity. Here we present experimental evidence from coherent three-dimensional electronic spectroscopy that the E to Z photoisomerization of phytochrome Cph1 is strongly nonadiabatic, and the simulations reproduce the measured features only when the photoisomerization proceeds nonadiabatically near, but not through, a conical intersection. The results broaden the general understanding of photoisomerization mechanisms and motivate future studies of nonadiabatic processes with multiple outcomes arising from branching on excited-state potential energy surfaces.

Original languageEnglish (US)
Pages (from-to)3550-3556
Number of pages7
JournalJournal of Physical Chemistry Letters
Issue number13
StatePublished - Jul 5 2019

ASJC Scopus subject areas

  • General Materials Science
  • Physical and Theoretical Chemistry


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