Monitoring molecular vibronic coherences in a bichromophoric molecule by ultrafast X-ray spectroscopy

The role of quantum-mechanical coherences in the elementary photophysics of functional optoelectronic molecular materials is currently under active study. Designing and controlling stable coherences arising from concerted vibronic dynamics in organic chromophores is the key for numerous applications. Here, we present fundamental insight into the energy transfer properties of a rigid synthetic heterodimer that has been experimentally engineered to study coherences. Quantum non-adiabatic excited state simulations are used to compute X-ray Raman signals, which are able to sensitively monitor the coherence evolution. Our results verify their vibronic nature, that survives multiple conical intersection passages for several hundred femtoseconds at room temperature. Despite the contributions of highly heterogeneous evolution pathways, the coherences are unambiguously visualized by the experimentally accessible X-ray signals. They offer direct information on the dynamics of electronic and structural degrees of freedom, paving the way for detailed coherence measurements in functional organic materials.

Automated summary

The role of quantum-mechanical coherences in the elementary photophysics of functional optoelectronic molecular materials is actively being studied, with designing and controlling stable coherences in organic chromophores being key for applications. An experimentally engineered rigid synthetic heterodimer offers fundamental insights into coherence study, with X-ray Raman signals used to monitor coherence evolution. Results show the vibronic nature of coherences surviving multiple conical intersection passages for hundreds of femtoseconds at room temperature, providing direct information on electronic and structural dynamics for coherence measurements in organic materials.