Radikale aus Polymethin‐Farbstoffen. IV—Dikation‐Radikale aus Polymethincyanin‐Farbstoffen mit Indolenin‐Endgruppen

Abstract

Dication radicals have been prepared by electrolytic oxidation of polymethinecyanine dyes. Their e.s.r. spectra c o b the expected structure of the radicals.

Cyanines during the 1990s: A Review

“…The probable favored dimerization sites are at the even methine carbons of the dye, and the process is reversible in the presence of alkyl substituents at these positions. From ESR studies, Oehling and Baer also proposed that the odd electron in the radical dication of cyanine and carbocyanine dyes resides at even-numbered methine carbons. The thermodynamic parameters for 77 are K d = 350 × 10 -7 M at 10 °C, Δ G = 5.6 kcal/mol, Δ H = 12.2 kcal/mol, and Δ S = 22.5 cal/mol·deg and those for 78 are K d = 7.0 × 10 -7 M at 10 °C, Δ G = 7.7 kcal/mol, Δ H = 16.4 kcal/mol, and Δ S = 29.8 cal/mol·deg.…”

Electrochromics by Intramolecular Redox Switching of Single Bonds

“…By using ESR spectroscopy [33,34] and MO calculations, [12,13] the highest spin densities of neutral cyanine radicals have been found to reside mainly at the odd methine carbon atoms, whereas in the corresponding radical dications the highest spin densities rest on the even methine carbon atoms as shown in Figure 1. Alkyl substitution in these positions will stabilize the radical state electronically but also render dimerization more difficult due to steric hindrance.…”