A modified calix[4]arene based receptor 2, conjugated with four bithiophene–cyanoacrylic acid groups, not only recognizes acidic amino acids (Asp and Glu) by quenching fluorescence, but also shows highly selective sensing for basic amino acids (Lys and Arg) by turning on fluorescence in sodium phosphate buffer solution without any organic solvent. The UV-Vis spectroscopy binding analysis and ESI-MS studies indicate that the above complexes have a 1 : 1 stoichiometry. ¹H NMR and molecular modeling studies suggest a supramolecular complex structure like the relationship between a lid and cup, but not a typical host-guest relationship of the cavity. A plausible mechanism involving intramolecular charge transfer (ICT) is proposed.