Redox-active, near-infrared dyes based on ‘Nindigo’ (indigo-N,N′-diarylimine) boron chelate complexes

Reactions of indigo-N,N'-diarylimine ('Nindigo') derivatives with BF sub(3).Et sub(2)O give mono- or bis-BF sub(2) chelate complexes 2 or 3 respectively. The product distribution between 2 and 3 is sensitive to the auxiliary base and solvent. Although the bis-BF sub(2) complexes 3 are...

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Bibliographic Details
Published in:Chemical science (Cambridge) 2013-01, Vol.4 (2), p.612-621
Main Authors: Nawn, Graeme, Oakley, Simon R., Majewski, Marek B., McDonald, Robert, Patrick, Brian O., Hicks, Robin G.
Format: Article
Language:English
Subjects:
Chelating
Derivatives
Electronic spectra
Electronics
Mathematical analysis
Oxidation
Reduction
Solvents
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Summary:Reactions of indigo-N,N'-diarylimine ('Nindigo') derivatives with BF sub(3).Et sub(2)O give mono- or bis-BF sub(2) chelate complexes 2 or 3 respectively. The product distribution between 2 and 3 is sensitive to the auxiliary base and solvent. Although the bis-BF sub(2) complexes 3 are isolable, they gradually decompose in solution to the corresponding mono-BF sub(2) species 2; this process is accelerated by water. The instability of 3 is believed to be due to ring stain effects based on structural analyses of 2. Electrochemical studies of 2 reveal one quasi-reversible oxidation process and two irreversible reductions, whereas derivatives of 3 possess a reversible oxidation and two sequential reversible reductions. The electronic spectra of 2 and 3 contain intense ( epsilon similar to 3 10 super(4) M super(-1) cm super(-1)) long-wavelength absorptions near 650 nm and 750 nm respectively. Both series of compounds are weakly emissive in the near-infrared. Time-dependent DFT calculations reveal the electronic transitions to be pi - pi * in nature.
ISSN:2041-6520
2041-6539
DOI:10.1039/C2SC21307A