NIR Absorbing Squaraines by Extension of the Conjugation with (Aminothiazolyl)ethenyl Groups
✍ Scribed by Herbert Meier; Ralf Petermann
- Publisher
- John Wiley and Sons
- Year
- 2004
- Tongue
- German
- Weight
- 163 KB
- Volume
- 87
- Category
- Article
- ISSN
- 0018-019X
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✦ Synopsis
Abstract
The bis{4‐{2‐[2‐(dialkylamino)thiazol‐5‐yl]ethenyl}‐2,6‐dihydroxyphenyl}squaraines 12a,b were synthesized from ethyl carbonochloridate (1) in six steps (Scheme). The donor–acceptor–donor systems 12a,b are dark blue dyes with absorption maxima in the NIR region, unless the measurements are performed in the presence of EtOH. In the latter case, the long‐wavelength band disappears, and the absorption in the UV region is strongly enhanced. The λ~max~ values in CHCl~3~ and CHCl~3~/EtOH differ by more than 450 nm. The completely reversible effect can be rationalized by the reversible degradation of intramolecular H‐bonds and a consequent torsion between the acceptor and the donor moieties.