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The interplay between ππ*/nπ* excited states in gas-phase thymine: a quantum dynamical study
David Picconi1, Vincenzo Barone, Alessandro Lami
1Scuola Normale Superiore, Piazza dei Cavalieri, 7 I-56126 Pisa, Italy.
Summary
A study on thymine
Area of Science:
- Quantum mechanics
- Photochemistry
- Molecular dynamics
Background:
- Thymine, a fundamental DNA base, exhibits complex excited-state dynamics.
- Understanding the interplay between bright ππ* and dark nπ* states is crucial for photochemistry.
- Gas-phase studies provide insights into intrinsic molecular behavior.
Purpose of the Study:
- Investigate the interplay between thymine's bright ππ* (S(π)) and dark nπ* (S(n)) excited states.
- Determine the likelihood and dynamics of population transfer between these states.
- Quantify the speed and efficiency of S(π)→S(n) population transfer.
Main Methods:
- Time-Dependent Density Functional Theory (TD-PBE0) for electronic structure calculations.
- Quantum dynamical simulations using a 3D anharmonic model.
- Quantum dynamical simulations employing a full-dimensional harmonic linear vibronic coupling model.
Main Results:
- Calculations reveal near-isoenergetic S(π) and S(n) states in relevant regions.
- A fast and effective S(π)→S(n) population transfer is predicted.
- Significant S(n) state population (20-40%) is observed as early as 50 femtoseconds, persisting over time.
Conclusions:
- The study confirms a rapid and efficient population transfer from the bright S(π) to the dark S(n) excited state in thymine.
- This ultrafast transfer mechanism is critical for understanding thymine's photochemical behavior and DNA photostability.
- The findings highlight the importance of non-adiabatic effects in excited-state dynamics of nucleobases.
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