TY - JOUR
T1 - Ultrafast Intersystem Crossing Dynamics of 6-Selenoguanine in Water
AU - Valverde, Danillo
AU - Mai, Sebastian
AU - Canuto, Sylvio
AU - Borin, Antonio Carlos
AU - González, Leticia
N1 - Funding Information:
D.V. acknowledges financial support from the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), under grants 2017/02612-4 and 2019/04413-4. S.C. thanks CAPES for the BioMol project 23038.004630/2014-35 and the National Institute of Science and Technology Complex Fluids (INCT-FCx) with the CNPq grant 141260/2017-3 and FAPESP grant 2014/50983-3. A.C.B. thanks the CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) for a research fellowship (project 311821/2021-9) and FAPESP for the research grant 2018/19454-5. S.M. and L.G. thank the University of Vienna for continuous support. Computations were performed on resources provided through the Superintendência de Tecnologia da Informação da Universidade de São Paulo and the Vienna Scientific Cluster (VSC3) in Austria.
Publisher Copyright:
© 2022 American Chemical Society. All rights reserved.
PY - 2022/7/25
Y1 - 2022/7/25
N2 - Rationalizing the photochemistry of nucleobases where an oxygen is replaced by a heavier atom is essential for applications that exploit near-unity triplet quantum yields. Herein, we report on the ultrafast excited-state deactivation mechanism of 6-selenoguanine (6SeGua) in water by combining nonadiabatic trajectory surface-hopping dynamics with an electrostatic embedding quantum mechanics/molecular mechanics (QM/MM) scheme. We find that the predominant relaxation mechanism after irradiation starts on the bright singlet S2state that converts internally to the dark S1state, from which the population is transferred to the triplet T2state via intersystem crossing and finally to the lowest T1state. This S2→ S1→ T2→ T1deactivation pathway is similar to that observed for the lighter 6-thioguanine (6tGua) analogue, but counterintuitively, the T1lifetime of the heavier 6SeGua is shorter than that of 6tGua. This fact is explained by the smaller activation barrier to reach the T1/S0crossing point and the larger spin-orbit couplings of 6SeGua compared to 6tGua. From the dynamical simulations, we also calculate transient absorption spectra (TAS), which provide two time constants (τ1= 131 fs and τ2= 191 fs) that are in excellent agreement with the experimentally reported value (τexp= 130 ± 50 fs) (Farrel et al. J. Am. Chem. Soc. 2018, 140, 11214). Intersystem crossing itself is calculated to occur with a time scale of 452 ± 38 fs, highlighting that the TAS is the result of a complex average of signals coming from different nonradiative processes and not intersystem crossing alone.
AB - Rationalizing the photochemistry of nucleobases where an oxygen is replaced by a heavier atom is essential for applications that exploit near-unity triplet quantum yields. Herein, we report on the ultrafast excited-state deactivation mechanism of 6-selenoguanine (6SeGua) in water by combining nonadiabatic trajectory surface-hopping dynamics with an electrostatic embedding quantum mechanics/molecular mechanics (QM/MM) scheme. We find that the predominant relaxation mechanism after irradiation starts on the bright singlet S2state that converts internally to the dark S1state, from which the population is transferred to the triplet T2state via intersystem crossing and finally to the lowest T1state. This S2→ S1→ T2→ T1deactivation pathway is similar to that observed for the lighter 6-thioguanine (6tGua) analogue, but counterintuitively, the T1lifetime of the heavier 6SeGua is shorter than that of 6tGua. This fact is explained by the smaller activation barrier to reach the T1/S0crossing point and the larger spin-orbit couplings of 6SeGua compared to 6tGua. From the dynamical simulations, we also calculate transient absorption spectra (TAS), which provide two time constants (τ1= 131 fs and τ2= 191 fs) that are in excellent agreement with the experimentally reported value (τexp= 130 ± 50 fs) (Farrel et al. J. Am. Chem. Soc. 2018, 140, 11214). Intersystem crossing itself is calculated to occur with a time scale of 452 ± 38 fs, highlighting that the TAS is the result of a complex average of signals coming from different nonradiative processes and not intersystem crossing alone.
KW - intersystem crossing
KW - nonadiabatic dynamics
KW - nucleobase analogues
KW - photobiology
KW - QM/MM
KW - transient absorption spectroscopy
KW - ultrafast processes
UR - http://www.scopus.com/inward/record.url?scp=85143784726&partnerID=8YFLogxK
U2 - 10.1021/jacsau.2c00250
DO - 10.1021/jacsau.2c00250
M3 - Article
AN - SCOPUS:85143784726
SN - 0002-7863
VL - 2
SP - 1699
EP - 1711
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 7
ER -