Molecules (Apr 2007)

Multi-step Redox Systems with NIR-Fluorescence Based on 4H-Imidazoles

  • Martin Matschke,
  • Rainer Beckert

DOI
https://doi.org/10.3390/12040723
Journal volume & issue
Vol. 12, no. 4
pp. 723 – 734

Abstract

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A new class of 4H-imidazoles was synthesized starting from fused-ring aromatic dinitriles. Strong bathochromic shifts of the longest wavelength absorptions were observed in the corresponding UV/vis spectra due to a conversion of the merocyanine chromophores into cyanines/(aza)oxonoles upon protonation/deprotonation of the 4H-imidazoles. Novel boratetraazapentalenes were synthesized via a cyclization reaction with boron trifluoride. These mesoionic species bearing a cyanine chromophore not only show NIR-fluorescence, they also participate as part of a quasi-reversible multi-step redox system. Large calculated semiquinone formation constants KSEM (3x1010 to 5x1011) indicate a high thermodynamic stability of the corresponding radical anions (SEM).

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