849667-83-0Relevant academic research and scientific papers
1H NMR spectral evidence for a specific host-guest complexation induced charge localization in squaraine dyes
Ajayaghosh, Ayyappanpillai,Arunkumar, Easwaran
, p. 3135 - 3138 (2005)
(Chemical Equation Presented) Experimental support is provided for the charge localization in squaraines, a class of fundamentally and technologically important organic dyes, by 1H NMR analysis through a host-guest complexation approach. Specific binding of Ca2+ ions to the squaraine 2 with a podand sidearm resulted in a charge-localized structure 2a with dramatic shifts and resolution of the proton signals when compared to those of 2.
Selective calcium ion sensing with a bichromophoric squaraine foldamer
Arunkumar, Easwaran,Ajayaghosh, Ayyappanpillai,Daub, Joerg
, p. 3156 - 3164 (2005)
Several squaraine tethered bichromophoric podand systems 1a-d and a monochromophoric analogue 2 were prepared and characterized. Among these, the bichromophore, 1b, containing five oxygen atoms in the flexible podand moiety was found to specifically bind Ca2+ in the presence of other metal ions such as K+, Na+, and Mg2+. The selective binding of Ca2+ is clear from the absorption and emission spectral changes as well as by the visual color change of 1b from light-blue to an intense purple-blue. Benesi-Hildebrand and Job plots confirmed a 1:1 binding between 1b and Ca2+. Signaling of the binding event is achieved by the cation-induced folding of the bichromophore and the resultant exciton coupling between the squaraine chromophores. The monochromophoric squaraine dye 2 failed to give optical signals upon Ca2+ binding, due to the absence of exciton interaction in the bound complex. Titration of the folded complex 9 with EDTA released the metal ion from the complex, thereby regaining the original absorption and emission properties of the bichromophore. The squaraine foldamer 1 b reported here is the first example of a selective chromogenic Ca2+ sensor, which works on the principle of exciton interaction in the folded Ca2+ complex of a bichromophore, the optical properties of which are similar to those of the "H"-type aggregates of analogous squaraine dyes.
