Effect of different alkyl groups on excited-state tautomerization of 7AI-azaindole-H 2 O: A theoretical study.

The effect of substituted alkyl groups at different substituted position on the first excited-state proton transfer of nR7AI-H2 O (n = 2-6; R = CH3 , C2 H5 , CF3 ) complexes were theoretically investigated at the TD-M06-2X/6-31 + G(d, p) level. Here n value denoted the substituted position Cn of R group. The replacement of alkyl R group had no effect on the features of HOMO and LUMO, but influenced the S0  → S1 adiabatic transition energies of the nR7AI-H2 O complex. Through computation, we found that the double proton transfer took place in a concerted but asynchronous protolysis pattern regardless of substituted group R and substituted position in the nR7AI-H2 O complex. The vibrational-mode specific nature of ESPT was verified. The alkyl group R changed the geometrical parameters of TS, and resulted in enlarging/narrowing the asynchronousity of ESPT. The ESPT barrier height was also affected by the substituted group and position.