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Updated: Sep 23, 2025

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Pre-Dewar structure modulates protonated azaindole photodynamics.

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Protonated 7-azaindole

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Area of Science:

  • Photochemistry
  • Theoretical Chemistry
  • Molecular Dynamics

Background:

  • Protonated azaindoles are important in photochemistry.
  • Experimental studies show differing excited-state lifetimes for protonated 7- and 6-azaindole.

Purpose of the Study:

  • To elucidate the reasons behind the significantly longer S3 state lifetime in protonated 7-azaindole compared to protonated 6-azaindole.
  • To investigate the nonradiative decay pathways of these isomers.

Main Methods:

  • Simulations of nonradiative decay pathways using trajectory surface hopping dynamics.
  • Analysis of excited-state topographies and nonadiabatic transition regions.

Main Results:

  • Both isomers primarily undergo ππ* relaxation from S3 to S1 on a subpicosecond timescale.
  • Protonated 6-azaindole readily accesses regions for nonadiabatic transitions.
  • Protonated 7-azaindole's internal conversion is hindered by a pre-Dewar bond formation and a boat conformation.

Conclusions:

  • The difference in S3 state lifetimes is attributed to distinct excited-state dynamics and conformational landscapes.
  • The formation of a pre-Dewar bond in protonated 7-azaindole significantly delays internal conversion, leading to its longer lifetime.