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The solution binding properties of calix[4]pyrroles with anion (as tetraalkylammonium salts) were investigated using UV-Vis spectroscopic techniques. The obvious red-shift of absorption maximum band of calix[4]pyrrole in EtOH in the presence of the tetramethylammonium (TMA+) salts or tetraethylammonium (TEA+) salts were observed, due to the charge-transfer interactions between the electron-rich pyrrole rings of calix[4]pyrroles and TMA+ or TEA+ cation subunit. The results indicated that calix[4]pyrrole receptors, which link the anionic species through multiple hydrogen bonding interactions, can use the periphery cavity for selectively binding cation subunits by cation-π charge-transfer interaction. The subsidiary interaction mode helps to further stabilize the calix[4]pyrrole-anion complex.
The apparent binding energy of calix [4] pyrroles with anion (as tetraalkylammonium salts) were investigated using UV-Vis spectroscopic techniques. The significant red-shift of absorption maximum band of calix [4] pyrrole in EtOH in the presence of the tetramethylammonium TMA +) salts or tetraethylammonium (TEA +) salts were observed, due to the charge-transfer interactions between the electron-rich pyrrole rings of calix [4] pyrroles and TMA + or TEA + which link the anionic species through multiple hydrogen bonding interactions, can use the peripheral cavity for selectively binding cation subunits by cation-π charge-transfer interaction. The subsidiary interaction mode helps to further stabilize the calix [4] pyrrole-anion complex.