Journal
CHEMICAL SCIENCE
Volume 13, Issue 18, Pages 5230-5242Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/d1sc06450a
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Funding
- Swiss NSF through the NCCR MUST
- German Academic Exchange Service (DAAD)
- Swiss National Science Foundation [200020 182184]
- Swiss National Science Foundation (SNF) [200020_182184] Funding Source: Swiss National Science Foundation (SNF)
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This study resolves the exciton dynamics of UV-excited adenosine single strands and offers a direct view into the coupling of electronic and structural dynamics in aggregated photochemical systems.
The photochemistry of DNA systems is characterized by the ultraviolet (UV) absorption of pi-stacked nucleobases, resulting in exciton states delocalized over several bases. As their relaxation sensitively depends on local stacking conformations, disentangling the ensuing electronic and structural dynamics has remained an experimental challenge, despite their fundamental role in protecting the genome from potentially harmful UV radiation. Here we use transient absorption and transient absorption anisotropy spectroscopy with broadband femtosecond deep-UV pulses (250-360 nm) to resolve the exciton dynamics of UV-excited adenosine single strands under physiological conditions. Due to the exceptional deep-UV bandwidth and polarization sensitivity of our experimental approach, we simultaneously resolve the population dynamics, charge-transfer (CT) character and conformational changes encoded in the UV transition dipoles of the pi-stacked nucleotides. Whilst UV excitation forms fully charge-separated CT excitons in less than 0.3 ps, we find that most decay back to the ground state via a back-electron transfer. Based on the anisotropy measurements, we propose that this mechanism is accompanied by a structural relaxation of the photoexcited base-stack, involving an inter-base rotation of the nucleotides. Our results finally complete the exciton relaxation mechanism for adenosine single strands and offer a direct view into the coupling of electronic and structural dynamics in aggregated photochemical systems.
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