A new 1,3,5-tris-triazole linked picolylimine conjugate of calix[6]arene (L) has been shown to be selective toward La 3+ by turn on fluorescence with ∼70-fold enhancement and emits blue, with a minimal detection limit of 65 ± 5 ppb (490 nM). The species of recognition has been modeled computationally to have a monocapped twisted square antiprism with a N 6O 3 binding core about La 3+. The in situ complex of L with La 3+ recognizes F – via fluorescence quenching. The reversible response of sensing La 3+ and F – sequentially by L has been demonstrated. © 2012 American Chemical Society.