Quantum Dynamics and Spectroscopy of Excited States

Quantum dynamics and spectroscopy of excited states probe the motion and transformations of molecules and materials following absorption of light. Excitation promotes electrons to higher electronic levels, creating non-equilibrium wavepackets that evolve on coupled potential energy surfaces. Competing pathways such as internal conversion and intersystem crossing govern nonradiative relaxation, while radiative transitions produce fluorescence and phosphorescence. Modern ultrafast spectroscopies—including femtosecond transient absorption and time-resolved infrared techniques—capture the subpicosecond to microsecond kinetics of these processes. Advances in theoretical quantum dynamics, from nonadiabatic wavepacket propagation to mixed quantum-classical methods, enable detailed mapping of excited-state landscapes and the role of vibronic and spin-orbit couplings. Together, experiment and simulation illuminate key mechanisms in photosynthesis, photocatalysis, organic electronics and photomedicine, where control over excited-state lifetimes and energy-transfer pathways underpins efficiency and selectivity.

Research from Nature Portfolio

Recent studies have highlighted the critical influence of Herzberg–Teller contributions on photoluminescence in polyacenes. Detailed calculations and corrected quantum-yield analyses reveal that first-order vibronic terms alone cannot account for observed efficiencies, necessitating second-order treatments to capture non-Franck–Condon effects. In one case, naphthalene exhibits a near-unity yield at the Franck–Condon point but retains unexpectedly high emission when Herzberg–Teller mixing is included, contrasting with anthracene and tetracene. This work emphasises that accurate modelling of excited-state decay channels must incorporate higher-order vibronic coupling to predict quantum yields reliably and guide the design of efficient organic emitters.

Quantum Dynamics and Spectroscopy of Excited States publication trend

The graph below shows the total number of articles in quantum dynamics and spectroscopy of excited states across all publications each year (not limited to Nature Index journals).

Technical terms

Internal conversion: Nonradiative transition between electronic states of the same spin multiplicity mediated by vibronic coupling.

Intersystem crossing: Spin‐forbidden transition between states of different multiplicity, often enhanced by spin‐orbit coupling.

Vibronic coupling: Interaction between electronic and nuclear (vibrational) degrees of freedom that enables nonadiabatic transitions.

Transient absorption spectroscopy: Ultrafast technique that tracks changes in absorption following photoexcitation to resolve excited‐state dynamics.

Franck–Condon principle: Approximation that electronic transitions occur vertically on the timescale of nuclear motion, defining the initial nuclear geometry of excited states.

Spin‐orbit coupling: Interaction between an electron’s spin and its orbital motion, facilitating spin‐forbidden processes such as intersystem crossing.

References

1. The slow photo-induced CO 2 release of N -phthaloylglycine. Chemical Science (2024).
2. Rapid calculation of internal conversion and intersystem crossing rate for organic materials discovery. The Journal of Chemical Physics (2022).
3. The dominant nature of Herzberg–Teller terms in the photophysical description of naphthalene compared to anthracene and tetracene. Scientific Reports (2022).
4. Ultrafast Excited State Dynamics of a Verdazyl Diradical System. Photochem (2024).