Photophysical properties of β-substituted free-base corroles

Inorg Chem. 2015 Mar 16;54(6):2713-25. doi: 10.1021/ic502860g. Epub 2015 Feb 25.

Abstract

Corroles are an emergent class of fluorophores that are finding an application and reaction chemistry to rival their porphyrin analogues. Despite a growing interest in the synthesis, reactivity, and functionalization of these macrocycles, their excited-state chemistry remains undeveloped. A systematic study of the photophysical properties of β-substituted corroles was performed on a series of free-base β-brominated derivatives as well as a β-linked corrole dimer. The singlet and triplet electronic states of these compounds were examined with steady-state and time-resolved spectroscopic methods, which are complemented with density functional theory (DFT) and time-dependent DFT calculations to gain insight into the nature of the electronic structure. Selective bromination of a single molecular edge manifests in a splitting of the Soret band into x and y polarizations, which is a consequence of asymmetry of the molecular axes. A pronounced heavy atom effect is the primary determinant of the photophysical properties of these free-base corroles; bromination decreases the fluorescence quantum yield (from 15% to 0.47%) and lifetime (from 4 ns to 80 ps) by promoting enhanced intersystem crossing, as evidenced by a dramatic increase in knr with bromine substitution. The nonbrominated dimer exhibits absorption and emission features comparable to those of the tetrabrominated derivative, suggesting that oligomerization provides a means of red-shifting the spectral properties akin to bromination but without decreasing the fluorescence quantum yield.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Absorption, Physicochemical
  • Crystallography, X-Ray
  • Dimerization
  • Models, Molecular
  • Molecular Conformation
  • Porphyrins / chemistry*
  • Quantum Theory
  • Spectrometry, Fluorescence

Substances

  • Porphyrins
  • corrole