Excited-State Dynamics in Nucleic Acid Photophysics

DNA and RNA bases absorb ultraviolet light, entering electronically excited states from which they must safely dissipate energy to avoid photodamage. Key deactivation pathways include ultrafast internal conversion through conical intersections back to the ground state, intersystem crossing to triplet manifolds and charge transfer between bases. These processes occur on femtosecond to picosecond timescales and are modulated by base sequence, stacking interactions, substituents and solvent environment. Advances in time-resolved spectroscopy—such as sub-30 fs transient absorption and multidimensional UV techniques—combined with mixed quantum-classical dynamics and high-level ab initio methods have elucidated the wavepacket evolution from the Franck–Condon region to excited-state minima. Detailed mapping of energy landscapes has revealed how structural features govern branching between photostable decay routes and potentially harmful pathways, such as lesion formation and dimerisation. Understanding these dynamics is vital for insights into prebiotic selection of photostable sequences, the mechanisms of DNA self-repair and the design of photoprotective agents.

Research from Nature Portfolio

Recent studies have tracked excited-state decay of pyrimidine nucleosides in real time, combining sub-30 fs transient absorption with mixed quantum-classical simulations. By monitoring the wavepacket journey from the Franck–Condon region into conical intersections, researchers distinguished the ultrafast deactivation of uridine from the slower decay of 5-methyluridine. The extended lifetime of the methylated analogue was attributed to solvent-mediated reorganisation delays in ring-opening motions that access the conical intersection, without significant involvement of the nπ* state. This work highlights how subtle structural modifications alter excited-state landscapes and influence photostability.

Excited-State Dynamics in Nucleic Acid Photophysics publication trend

The graph below shows the total number of articles in excited-state dynamics in nucleic acid photophysics across all publications each year (not limited to Nature Index journals).

Technical terms

Franck–Condon region: The starting geometry of a molecule immediately after photon absorption, before nuclear relaxation occurs.

Conical intersection: A point where two electronic potential energy surfaces intersect, facilitating ultrafast nonradiative transitions.

Nonadiabatic dynamics: Nuclear motion in which electronic and vibrational states evolve concurrently, often leading to rapid state switching.

Charge transfer state (CT state): An excited state in which an electron has been transferred between adjacent nucleobases.

Internal conversion (IC): A nonradiative process in which an excited molecule returns to the ground state through vibrational energy redistribution.

Transient absorption spectroscopy: A time-resolved technique that measures changes in absorption following ultrafast excitation.

References

1. Tracking excited state decay mechanisms of pyrimidine nucleosides in real time. Nature Communications (2021).
2. Photoinduced charge separation and DNA self-repair depend on sequence directionality and stacking pattern. Chemical Science (2024).
3. Factors Affecting the Population of Excited Charge Transfer States in Adenine/Guanine Dinucleotides: A Joint Computational and Transient Absorption Study. Biomolecules (2024).