Research
Watching—and Controlling—Molecules in Motion
The absorption of light launches a molecule far from equilibrium. Electrons redistribute, bonds begin to move, surrounding molecules reorganize, and electronic states can change character—all within femtoseconds to picoseconds. These earliest motions often determine the ultimate outcome of a photochemical process.
The Rather Research Group uses state-of-the-art ultrafast laser spectroscopy to uncover how coupled electronic and nuclear dynamics govern the behavior of photoexcited molecules and materials. We are particularly interested in identifying the molecular motions that drive processes such as charge transfer, excited-state symmetry breaking, singlet fission, spin conversion, and energy relaxation.
A central theme of our research is that nuclear motion is not simply a response to electronic excitation. Specific vibrations can actively direct electronic evolution. By resolving these motions in real time, we aim to establish new ways of understanding—and ultimately controlling—excited-state dynamics.
Coherent Nuclear Motion and Excited-State Dynamics
Chemical transformations occur through nuclear motion, yet many ultrafast spectroscopies primarily track changes in electronic populations. We use broadband, few-femtosecond spectroscopy to directly resolve the coherent vibrational wavepackets launched by photoexcitation.
The frequencies, phases, amplitudes, and dephasing of these oscillations provide a direct window into how the molecular structure evolves on excited- and ground-state potential energy surfaces. We are developing approaches that use these wavepackets as structural reporters of processes such as electronic localization, charge redistribution, and excited-state relaxation.
Our longer-term goal is to move from observing these motions to determining whether selected vibrational coordinates can be deliberately excited or synchronized to steer photochemical dynamics along desired pathways.
Excited-State Symmetry Breaking and Charge Transfer
In many multichromophoric molecules, photoexcitation initially creates an electronically delocalized state that subsequently localizes through interaction with molecular vibrations and the surrounding environment. This spontaneous excited-state symmetry breaking can dramatically alter excited-state energies, charge distributions, fluorescence, and chemical reactivity.
We investigate how molecular structure, solvent environment, and nuclear motion control the transition from delocalized to charge-localized excited states. Using ultrafast spectroscopy together with steady-state photophysics and theoretical calculations, we seek to determine which molecular coordinates initiate symmetry breaking and how this structural evolution controls subsequent charge-transfer and nonradiative pathways.
Understanding these relationships provides fundamental design principles for manipulating excited states in molecular materials used for light emission, energy conversion, and photochemistry.
Singlet Fission and Correlated Spin States
Singlet fission converts one photoexcited singlet exciton into two triplet excitons and provides a compelling example of how molecular packing, electronic coupling, nuclear motion, and spin dynamics become intertwined.
We investigate singlet fission across molecular systems with systematically varied intermolecular coupling and solid-state structure. Ultrafast spectroscopy allows us to follow the formation and evolution of correlated triplet-pair states, while complementary spin-sensitive measurements reveal their subsequent spin dynamics and separation.
A major focus of our work is understanding how molecular architecture and electronic coupling determine the pathway of singlet fission.
Ultrafast Dynamics in Emerging Materials
The same fundamental questions extend beyond molecular photochemistry to semiconductor and quantum materials. We use broadband transient absorption and coherent spectroscopy to investigate how photoexcited carriers interact with their surrounding lattice.
These measurements allow us to follow carrier cooling, excitonic dynamics, electron–phonon coupling, and coherent phonon motion across a wide spectral and temporal range. By connecting electronic relaxation with specific lattice vibrations, we aim to understand how microscopic structural dynamics influence the optical and electronic properties of low-dimensional materials.
Our Approach
Our research combines ultrafast transient absorption spectroscopy, broadband pump–probe spectroscopy, global and target kinetic analysis, steady-state optical spectroscopy, and collaborative theoretical and magnetic-resonance methods.
A particular strength of the group is the development and application of few-femtosecond broadband spectroscopy, which allows us to simultaneously observe electronic-state evolution and the nuclear wavepackets that accompany it.
Across all of our projects, we ask a common question:
Which molecular motions determine what happens after a molecule absorbs light—and can we use those motions to control the outcome?
