Ultrafast Dynamics in DNA and RNA Derivatives Monitored by Broadband Transient Absorption Spectrscopy By Matthew M. Brister and Carlos E. Crespo-Hernández 1

Outline Introduction – Photochemistry of DNA/RNA Methods – Broadband Transient Absorption Spectroscopy Proposed Kinetic Models Nucleic Acid Derivatives Results Summary Acknowledgments 2

Introduction DNA/RNA rather Photo-stable UV Irradiation causes damage to DNA and RNA – Carcinogenesis – Mutagenesis Why? – High-Energy Electronic States 3 Pollum, M.; Martínez-Fernández, L.; Crespo-Hernández, C. E. Top. Curr. Chem. 2015, 335, 245–327.

Ultra-fast Broadband Transient Absorption Spectroscopy 4 SoSo S1S1 SnSn Pump Internal Conversion Intersystem Crossing Fluorescence T1T1 TnTn Non-radiative Decay Non-radiative Decay Non-radiative Decay Non-radiative Decay Phosphorescence Turro, N. J. In Modern Molecular Photochemistry; University Science Books: Sausalito, 1991; pp. 4–5. Ruckebusch, C.; Sliwa, M.; Pernot, P.; de Juan, a.; Tauler, R. J. Photochem. Photobiol. C Photochem. Rev. 2012, 13, 1–27. Wavelength (nm) ΔAΔA Spectral Evolution Time (ps) Probe

Computational Kinetic Models 5 S 1 (n,π*) S0S0 S 2 (π,π*) T 1 (π,π*) S 0 (hot) T 2 (n,π*) ~5 ps Etinski, M.; Fleig, T.; Marian, C. M. J. Phys. Chem. A 2009, 113, 11809– Richter, M.; Mai, S.; Marquetand, P.; Gonzalez, L. Phys. Chem. Chem. Phys. 2014, 16, 24423– ~2.4 ps ~5 ps Etinski: DFT/MRCI Richter: ab initio

Experimental Kinetic Model 6 S 1 (n,π*) S0S0 S 2 (π,π*) T 1 (π,π*) S 0 (hot) T 2 (n,π*) S 1 (hot) < 10 ps Hare, P. M.; Crespo-Hernández, C. E.; Kohler, B. J. Phys. Chem. B 2006, 110, 18641–18650.

Why Nucleic Acid Derivatives Monitor Triplet State Formation – Most reactive – No consensus of the time scale of the formation Use of Nucleic Acid Derivatives – Increase solubility – Increase Triplet yield 7 R = H Uracil R = 1-Cyclohexyluracil (1CHU) Pollum, M.; Martínez-Fernández, L.; Crespo-Hernández, C. E. Top. Curr. Chem. 2015, 335, 245–327. Hare, P. M.; Crespo-Hernández, C. E.; Kohler, B. J. Phys. Chem. B 2006, 110, 18641– Kwok, W.-M.; Ma, C.; Phillips, D. L. J. Am. Chem. Soc. 2008, 130, 5131–5139. Richter, M.; Mai, S.; Marquetand, P.; Gonzalez, L. Phys. Chem. Chem. Phys. 2014, 16, 24423–24436.

Contour Plot of 1CHU 8 ∆A Pump Pulse 270 nm Excitation ~200 ± 50 fs time Probe Pulse WLC from CaF 2 Crystal Spectral Range 325 to 700 nm

Spectral Evolution of 1CHU ps ps 0.60 ps Steady-State Spectra of 1CHU S2S2 S 0 (hot) + S 1 (hot) S 1 (Relaxed) + T 1

Kinetic Traces at Specific Broadband Wavelengths 10 S2S2 S 0 (hot) S1S1 T1T1

Lifetimes 11 Lifetime (ps) 2 × Standard Deviation (ps) Tau Tau Tau * IRF: 200 fs

Decay Associated Spectra 12 S2S2 S 1 (hot) + S 0 (hot) S 1 (Relaxed) + T 1 T 1 (only) [3 × DAS]

Kinetic Model 13 Hare, P. M.; Crespo-Hernández, C. E.; Kohler, B. J. Phys. Chem. B 2006, 110, 18641– > 3 ns

Summary Obtain Triplet State Formation – ISC Lifetime ≤ 3.17 ± 0.06 ps Intersystem Crossing (ISC) Lifetime Faster than previously thought Supports the Kinetic model of Hare et al. 14

Acknowledgments National Science Foundation (CHE ) Dr. Carlos Crespo Group Members – Marvin Pollum – Nicholas Dunn – Regina DiScipio 15

Questions ? 16

Kinetic Model 17 S 1 (n,π*) S0S0 S 1 (hot) S 2 (π,π*) T 1 (π,π*) S 0 (hot) 0.28 ps 0.34 ps 3.17 ps Hare, P. M.; Crespo-Hernández, C. E.; Kohler, B. PNAS 2007, 104, 435–440. Hare, P. M.; Crespo-Hernández, C. E.; Kohler, B. J. Phys. Chem. B 2006, 110, 18641–18650.

Decay Associated Spectra 18 S2S2 S 0 (hot) + S 1 (hot) S 1 (Relaxed) + T 1 T 1 (only)

Why Nucleic Acid Derivatives 19 Ground State Absorption

Broadband Transient Absorption Spectroscopy 20 Wavelength (nm) ΔAΔA Time (ps) 0 Probe Pump Time (ps) ΔAΔA Kinetic Trace at Specific Wavelength Spectral Evolution Ruckebusch, C.; Sliwa, M.; Pernot, P.; de Juan, a.; Tauler, R. J. Photochem. Photobiol. C Photochem. Rev. 2012, 13, 1–27. Time (ps)