Theoretical Investigation On The Excited-state Intermolecular Proton Transfer

A systematic study on the first excited-state intermolecular double proton transfer in2XAI-H₂O?X=F,Cl,Br?,2RAI-H₂O?R=OH,OCH₃;CN,NO₂,CHO?and nXAI-H₂O?n=3,5,6,7;X=F,Cl,Br?complexes were investigated by using TD-M06-2X method with 6-31+G?d,p?basis set in solution.The excited-state double proton transfer in the above complexes took place in a concerted but asynchronous protolysis pathway.The vibrational-mode of excited-state intermolecular double proton transfer in 2XAI-H₂O?X=F,Cl,Br?and 2RAI-H₂O?R=OH,OCH₃;CN,NO₂,CHO?complexes were confirmed.The specific vibrational-mode could shorten the reaction path and lead to accelerate the reaction rate.The substituent effects of different groups on the excited-state intermolecular proton transfer thermodynamics and kinetics were discussed.It was obvious that the geometrical parameters,barrier height,asynchrony and specific vibrational-mode of excited-state intermolec-ular proton transfer changed with the different substituent groups.The sum of the N₁-O₁₁1 and O₁₁-N₈distances in the 2XAI-H₂O?X=H,F,Cl,Br?complexes was liner dependence on the ZPE-corrected barrier height.The changes in the sum of the N₁-O₁₁1 and O₁₁-N₈ distances,in the NBO charge of H₃O⁺-part in the TS,and in the ZPE-corrected barrier height were all have good correlations with Pauling electronegativity of halogen atom X in the 2XAI-H₂O?X=H,F,Cl,Br?complexes.The sum of the N₁-O₁₁1 and O₁₁-N₈ distances in the 2RAI-H₂O?R=OH,OCH₃;CN,NO₂,CHO?complexes was linearly dependent on the ZPE-corrected barrier height of excited-state proton transfer.The substitution position had a significant effect on the excited-state proton transfer reaction.The substituent of halogen atom at C₂?C₃ and C₅?C₆?C₇ positions resulted in changing the geometrical parameters obviously in the nXAI-H₂O?n=2,3,5,6,7;X=F,Cl,Br?complexes.The substituent of halogen atom at C₂?C₃ position reduced the barrier height and the substituent of halogen atom at C₅?C₇ position increased the barrier height.And the replacement of X at C₆position made the barrier height rise/reduce due to the substituent halogen atom X.The sum of the N₁-O₁₁and O₁₁-N₈ distances in the nXAI-H₂O?n=2,3,5,6,7;X=F,Cl,Br?complexes was linearly dependent on the ZPE-corrected barrier height of excited-state proton transfer.