1,3-indane-based chromogenic calixpyrroles with push-pull chromophores: synthesis and anion sensing.

TLDR: Knoevenagel condensation of 2-formyl-octamethylcalix with selected 1,3-indanedione derivatives yields calix[4]pyrrole anion sensors with push-pull chromophores displaying strong intramolecular charge transfer that results in augmented signal output and dramatic changes in anion selectivity.

About: This article is published in Organic Letters.The article was published on 2006-01-10 and is currently open access. It has received 131 citations till now. The article focuses on the topics: Knoevenagel condensation & Indane.

Figures

Figure 1. Structures of sensors2-4 designed for tuning of anion affinity, selectivity, and also a degree of color response.

Figure 3. X-ray structures of sensors1 (left) and 2 (2DMSO) (right) with an integrated calixpyrrole indan-1-ylidene chromophore.

Figure 2. Anion-hydrogen bonding results in partial charge transfer from electron-rich pyrrole to electron-poor indanylidene.

Figure 6. 1H NMR spectra (selected regions) of sensor2 (10 mM) in DMSO-d6 titrated by fluoride. The NH andâ-pyrrole CH proton resonances in free and complexed sensor2 are labeled as follows: NHfree, CHfree, NHcomplex, and CHcomplex.

Figure 7. Absorption spectra of sensor3 (50µM in DMSO) titrated by fluoride. Absorption spectra (left) and binding isotherms derived from absorbance at 460 and 515 nm (right).

Figure 4. Structure and absorption spectra of sensors1 (black line), 2 (blue line),3 (orange line), and4 (pink line) in CH2Cl2 (50 µM). Inset shows solutions.

Frequently asked questions

Q1. What have the authors contributed in "1,3-indane-based chromogenic calixpyrroles with push-pull chromophores: synthesis and anion sensing" ?

Here, by using 1H NMR, the authors demonstrate that the anion binding is the prevalent process. The authors were concerned that the dramatic changes in color and the high binding constants might be caused by deprotonation of the acidic NH of the dye pyrrole rather than ( 11 ) Hydrated tetrabutylammonium ( TBA ) salts of the anions were used in this study: fluoride ( ×6H2O ), chloride, phosphate ( ×2H2O ), and pyrophosphate ( ×2H2O ). 360 Org. Lett., Vol. 8, No. 3, 2006 Visual inspection of solutions of sensors 1-4 ( 50 μM in CH2Cl2 or DMSO with 0. 5 % water ) before and after the addition of anion salts11 showed a dramatic change in color in the case of fluoride, acetate, and, to a lesser extent, dihydrogenphosphate, suggesting strong binding, whereas the addition of chloride, bromide, or nitrate resulted in weak or no changes in color ( Figure 5 ).