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<p>The current research aims to explain the high photostability of the Watson–Crick base pair isoguanine (iG)–isocytosine (iC) in water solution. In this order, five conical intersections S<sub>0</sub>/S<sub>1</sub> connected with ring deformations of the two nucleobases in the base pair were optimized and involved in mechanisms of excited-state relaxations to the ground state in water surroundings. For the first time, we reported a conical intersection S<sub>0</sub>/S<sub>1</sub> connected with imidazole ring deformation of iG. However, it was found that the most relevant mechanism is connected with the iG deformation at the C–NH<sub>2</sub> fragment. This study is a part of the global research, the purpose of which is to explain the high photostability of nucleobases which directly reflects the photostability of life. The mechanisms were studied at the TD DFT (B3LYP, CAM-B3LYP, and M06-2X) with PCM (water) and CC2 levels of theory with aug-cc-pVDZ basis functions.</p> Graphical Abstract <p></p>

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Non-radiative relaxation of the excited states of the base pair isogunine–isocytosine through conical intersections S0/S1 connected with ring puckering

  • 期刊论文

  • 发表日期：

    2026年4月13日

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  • Vassil B. Delchev,
  • Ernst Horkel

摘要

The current research aims to explain the high photostability of the Watson–Crick base pair isoguanine (iG)–isocytosine (iC) in water solution. In this order, five conical intersections S0/S1 connected with ring deformations of the two nucleobases in the base pair were optimized and involved in mechanisms of excited-state relaxations to the ground state in water surroundings. For the first time, we reported a conical intersection S0/S1 connected with imidazole ring deformation of iG. However, it was found that the most relevant mechanism is connected with the iG deformation at the C–NH2 fragment. This study is a part of the global research, the purpose of which is to explain the high photostability of nucleobases which directly reflects the photostability of life. The mechanisms were studied at the TD DFT (B3LYP, CAM-B3LYP, and M06-2X) with PCM (water) and CC2 levels of theory with aug-cc-pVDZ basis functions.

Graphical Abstract