Anion-induced switching of the helical orientation of a chiral indolocarbazole dimer

作者：Lee Hyun Ji; Jeon Hae Geun; Jeong Kyu Sung^*

来源：Supramolecular Chemistry, 2015, 27(5-6): 378-385.

DOI：10.1080/10610278.2014.941293

• hydrogen bond
• helicity
• anion binding
• indolocarbazole
• urea

An indolocarbazole dimer, containing chiral urea appendages, that adopts a helically folded conformation by intramolecular hydrogen bonds as proven by H-1 NMR and circular dichroism (CD) spectroscopy has been prepared. Owing to the preferential formation of one helical conformer, strong CD signals appear in relatively non-polar solvents such as chloroform (CHCl3) and dichloromethane (CH2Cl2) but the signal is negligible in dimethyl sulfoxide (DMSO). In addition, the optical rotation of the dimer is highly sensitive to the polarity of solvents. For example, the magnitude of the specific rotation ([alpha](D)) is -934 degrees in CH2Cl2 and -657 degrees in CHCl3 but it is only -75 degrees in DMSO. These observations suggest that the dimer folds to a helical structure by intramolecular hydrogen bonds in relatively non-polar solvents but exists in an unfolded extended conformation in polar solvents such as DMSO. The dimer strongly binds anions such as chloride, acetate and sulfate by multiple hydrogen bonds. In addition, anion binding leads to considerable CD spectral changes with the different pattern and degree of Cotton effects depending on the kind of anions. The dimer may be therefore utilised for the construction of an anion-responsive chiroptical sensor or switch.

• 出版日期2015-6-3