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Excited state intramolecular proton transfer (ESIPT) occurs rapidly in SAA and DHAQ systems. Higher energy excitation affects product yield and vibrational patterns, not the core ESIPT rate.

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Area of Science:

  • Physical Chemistry
  • Spectroscopy
  • Quantum Mechanics

Background:

  • Excited state intramolecular proton transfer (ESIPT) is a crucial photophysical process.
  • Ultrafast dynamics in ESIPT systems are not fully understood, especially upon excitation to higher energy states.

Purpose of the Study:

  • To investigate ESIPT dynamics in salicylaldehyde azine (SAA) and 1,5-dihydroxyanthraquinone (DHAQ) upon excitation to higher excited states (Sn).
  • To delineate the ultrafast photophysics and understand the influence of excitation energy on ESIPT.

Main Methods:

  • Transient absorption spectroscopy with sub-30 fs pulses and broadband visible probing.
  • Steady-state measurements and Time-Dependent Density-Functional Theory (TD-DFT) calculations.

Main Results:

  • In SAA, ESIPT occurred in ~30 fs, with wavelength-dependent coherent vibrational beats influenced by the excited state.
  • In DHAQ, ESIPT showed a primary time-constant of ~85 fs and a slower component of 9 ps.
  • The ESIPT rate was invariant to excitation energy, but product yield and coherent oscillations varied.

Conclusions:

  • Ultrafast ESIPT rates are largely independent of excitation energy.
  • Higher energy excitation can alter product yields and vibrational coherences due to alternative decay pathways.