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Halogen substituent effect on the water-assisted excited-state tautomerization of 2, 7-diazaindole-H2O complex in
1Department of Chemistry and Material Science, College of Science, Nanjing Forestry University, Nanjing 210037, People's Republic of China.
Abstract:
We studied the ESPT process in the 2-DAI-H2O complex theoretically for the first time, and compared the kinetics of 2-DAI-H2O with those features of 7-DAI-H2O. The substituted effect on the dynamics of excited-state double proton transfer in 2-DAI-H2O and 7-DAI-H2O clusters in water were also investigated at the TD-M06-2X/6-311+G(d, p) level. In this work, 2,7-DAI-H2O is also expressed as 2-DAI-H2O and 7-DAI-H2O, in which correspond to different ESPT reactions and generate two tautomers (N2H form and N7H form). In both the 2-DAI-H2O and 7-DAI-H2O complexes, ESPT processes happened in a concertedly but asynchronously protolysis pathway. The ESPT process preferred to occur in the 7-DAI-H2O complex due to its lower barrier height. For the 3-X-2-DAI-H2O and 3-X-7-DAI-H2O (X = H, F, Cl, Br) complexes, the replacement of halogen atom did not influence the ESPT mechanism. However, the replacement of halogen atom changed the structural parameters evidently, reduced the barrier height up to 4-5 kcal/mol, and enlarged the asynchronicity of ESPT apparently. ∆(R1+R2) values in the 3X-2-DAI-H2O and 3X-7-DAI-H2O complexes have linear correlation to the ZPE-corrected ESPT barrier height linearly.
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