Unexpected photophysical properties of symmetric indolylmaleimide derivatives

J Phys Chem A. 2005 Jul 28;109(29):6440-9. doi: 10.1021/jp051035u.

Abstract

Arcyriarubin A and arcyriaflavin A, two strongly emissive and intensely colored natural products containing both two indoles and a maleimide unit, are investigated (in the flavin the two indole moieties are coupled by a cyclization). The photophysical properties of these compounds were studied in several solvents using UV-vis absorption, steady-state and time-resolved emission, nano- and femtosecond transient absorption spectroscopy. Furthermore, the effect of complexation with zinc(II) 1,4,7,11-tetraazacyclododecane on the photophysical properties of these natural products has been investigated. The chemical structures of the compounds would suggest a charge transfer (CT) character in the ground and/or excited states, since indole is a well-known electron donor and maleimide is a good electron acceptor. Their solvatochromic behavior was investigated by using the Kamlet-Taft approach and indicates only a small CT character in the excited state. This is substantiated by the time-resolved spectroscopy and the complexation study. Molecular orbital calculations indicate that there are no electronic transitions in which a large electron density is transferred from one indole unit to the maleimide part. All calculated orbitals show a strong delocalization of the electron density over the whole molecule. These findings corroborate the experimental results. Whereas the two compounds do have a substantial (calculated) ground-state dipole moment (6 D) and show some solvatochromic behavior, they behave more like conjugated aromatic systems than like electron donor-acceptor systems.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Indoles / chemistry*
  • Maleimides / chemistry*
  • Methylation
  • Models, Molecular
  • Molecular Structure
  • Photochemistry
  • Solvents
  • Spectrophotometry
  • Stereoisomerism
  • Temperature

Substances

  • Indoles
  • Maleimides
  • Solvents