Squaraine dye

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Squaraine Dyes are a class of organic dyes which posses very intense fluorescence spectra in the near infrared region. (excitation are typically around 620nm and fluorescence are typically upward of 660-670nm for aniline derivatives). They are typically encumbered by nucleophilic attack of the central squaric acid derivative which is highly electron deficient. This encumbrance can be attenuated by the formation of a rotaxane around the dye to protect it from nucleophiles. They are currently used as sensors for ions and have recently, with the advent of protected squanaine derivatives, been exploited in biomedical imaging.

They are synthetically derived from squaric acid which undergoes an electrophilic aromatic substitution reaction with an aniline or another electron rich aromatic derivative to form a highly conjugated product with extensive charge distribution.

References

• Selective Calcium Ion Sensing with a Bichromophoric Squaraine Foldamer E. Arunkumar, A. Ajayaghosh, J. Daub J. Am. Chem. Soc. 2005, 127, 3156-3164
• Selective Proton Controlled Intramolecular Photoinduced Electron Transfer (PET) in Podand Linked Squaraine–Aniline Dyads E. Arunkumar, A. Ajayaghosh. Chem. Commun. 2005, 599-601
• A Controlled Supramolecular Approach Towards Cation Specific Chemosensors: Alkaline Earth Metal Ion-Driven Exciton Signaling in Squaraine Tethered Podands. E. Arunkumar, P. Chithra, A. Ajayaghosh. J. Am. Chem. Soc. 2004, 126, 6590-6598
• A Highly Specific Ca2+-ion Sensor: Signaling By Exciton Interaction in a Rigid-Flexible-Rigid Bichromophoric "H"-foldamer A. Ajayaghosh, E. Arunkumar, J. Daub. Angew. Chem. Int. Ed. 2002, 41, 1766-1769
• Squaraine-Derived Rotaxanes: Highly Stable Fluorescent Near-IR dyes E. Arunkumar, N. Fu, B. D. Smith. Chem. Eur. J. 2006, 12, 4684-4690
• Squaraine Derived Rotaxanes: Sterically Protected Fluorescent Near-IR Dyes E. Arunkumar, C. C. Forbes, B. C. Noll, B. D. Smith. J. Am. Chem. Soc. 2005, 127, 3288-3289

External links

• Bradley Smith Research Group. Developing Squaraine based rotaxane dyes which are extremely stable to aqueous environments.. Retrieved on November 4, 2005.