Position of the Benzene Ring Substituent Regulates the Excited-State Deactivation Process of the Benzyluracil Systems

Abstract

A systematic theoretical study of the regulating effect of the substituent position on the photoinduced deactivation process of the benzyluracil systems has been performed based on the high-level static electronic structure calculations and on-the-fly full-dimensional excited-state dynamics simulations. Similarities and differences coexist for the two systems by comparative studies on the photoinduced deactivation process of the 5-benzyluracil (5-BU) and 6-benzyluracil (6-BU) systems. They both obey an S2 → S1 → S0 two-step decay pattern, and the decay coordinates of the S2 → S1 and S1 → S0 processes are mainly driven by the elongation of the bridging bond and the out-of-plane ring deformation motion, respectively. However, the puckering motion occurring at the C2 atom in the uracil fragment dominates the decay pathway of the 5-BU system. On the contrary, the puckering motion at the C5 atom in the benzene fragment mainly drives the decay coordinate of the 6-BU system. Therefore, the substituent position could play significant roles in the deactivation process of the benzyluracil systems. Moreover, the S1 → S0 decay process of the 6-BU system consists of five pathways, possessing a more complex deactivation picture than the 5-BU system. The fitted time scale of the puckering motion is compatible with the experimentally observed lifetimes. This work provides a fundamental understanding of the photophysical and photochemical properties of the benzyluracil systems and can give rational suggestions to further design or regulate the bionic molecular systems.

Excited-state dynamics of 3-hydroxychromone in gas phase

“…The photoinduced deactivation dynamics of 3-HC were followed by performing the on-the-fly surface hopping dynamics simulation procedure NAIMD-DICP, which has been successfully employed to study the deactivation process of many different molecular systems. [41][42][43][44][45][46] The nuclear trajectory propagation was integrated with the velocity Verlet algorithm. 47 The transition probability between different electronic states was estimated based on the Zhu-Nakamura theory, [48][49][50][51] which was compared with a random number generated between 0 and 1 to determine whether to hop or not.…”

Revealing the excited-state dynamics of cytidine and the role of excited-state proton transfer process

“…Further computational details can be found in the previous publications. 41,50–52 Taking the nπ* state into consideration, all the trajectories started exclusively from the S 2 state. A total of 58 and 45 trajectories were calculated for syn -Cyd and anti -Cyd, respectively, with the maximal simulation time of 250 fs.…”

Theoretical Study of Light-Induced Crosslinking Reaction Between Pyrimidine DNA Bases and Aromatic Amino Acids

“…Given that these photochemical reactions are very difficult to follow, theoretical modeling can reveal many small details in addition to a global understanding of the processes and thus explain intermediate steps that we cannot observe with our experimental tools ( Kleinermanns et al, 2013 ; González et al, 2016 ). Accordingly, the model system of benzyluracil was also intensively investigated considering different theoretical frameworks, and several photoreaction mechanisms were proposed ( Micciarelli et al, 2013 ; Micciarelli et al, 2014 ; Bende and Toşa, 2015 ; Micciarelli et al, 2017 ; Valadan et al, 2019 ; Zhao et al, 2021 ).…”

“…In contrast, a simpler photochemical reaction can also take place between two nearby aromatic systems. This phenomenon is known in the literature as thymine dimerization ( Boggio-Pasqua et al, 2007 ; Schreier et al, 2007 ; Law et al, 2008 ; Kancheva and Delchev, 2016 ; Mendieta-Moreno et al, 2016 ; Zhao et al, 2021 ). This kind of reaction mechanism does not include any intermediate steps of charge or proton transfer as well as of radical ion pair formation, just a formation of a cyclic adduct (CA) between unsaturated fragments of two molecules.…”