Influence of local microenvironment on the double hydrogen transfer in porphycene

Piotr Kasprzycki , Przemysław Kopyck, Arkadiusz Listkowski, Aleksander Gorski, Czesław Radzewicz, David J. S. Birch, Jacek Waluk, Piotr Fita

Research output: Contribution to journalArticle

Abstract

We performed time-resolved transient absorption and fluorescence anisotropy measurements in order to study tautomerization of porphycene in rigid polymer matrices at cryogenic temperatures. Studies were carried out in poly(methyl methacrylate) (PMMA), poly(vinyl butyral) (PVB), and poly(vinyl alcohol) (PVA). The results prove that in all studied media hydrogen tunnelling plays a significant role in the double hydrogen transfer which becomes very sensitive to properties of the environment below approx. 150 K. We also demonstrate that there exist two populations of porphycene molecules in rigid media: “hydrogen-transferring” molecules, in which tautomerization occurs on time scales below 1 ns and “frozen” molecules in which double hydrogen transfer is too slow to be monitored with nanosecond techniques. The number of “frozen” molecules increases when the sample is cooled. We explain this effect by interactions of guest molecules with a rigid host matrix which disturbs symmetry of porphycene and hinders tunnelling. Temperature dependence of the number of hydrogen-transferring molecules suggests that the factor which restores the symmetry of the double-minimum potential well in porphycene are intermolecular vibrations localized in separated regions of the amorphous polymer.
Original languageEnglish
Pages (from-to)17117-17128
Number of pages12
JournalPhysical Chemistry Chemical Physics
Volume22
Issue number30
Early online date13 Jul 2020
DOIs
Publication statusPublished - 14 Aug 2020

Keywords

  • time-resolved transient absorption
  • fluorescence anisotropy
  • cryogenic temperatures
  • hydrogen tunnelling
  • double hydrogen transfer

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    Kasprzycki , P., Kopyck, P., Listkowski, A., Gorski, A., Radzewicz, C., Birch, D. J. S., Waluk, J., & Fita, P. (2020). Influence of local microenvironment on the double hydrogen transfer in porphycene. Physical Chemistry Chemical Physics, 22(30), 17117-17128. https://doi.org/10.1039/D0CP02687E