Anion-coordination-induced turn-on fluorescence of an oligourea- functionalized tetraphenylethene in a wide concentration range

A tetrakis(bisurea)-decorated tetraphenylethene (TPE) ligand (L ²) was designed, which, upon coordination with phosphate ions, displays fluorescence "turn-on" over a wide concentration range, from dilute to concentrated solutions and to the solid state. The fluorescence enhancement can be attributed to the restriction of the intramolecular rotation of TPE by anion coordination. The crystal structure of the A₄L ₂ (A=anion) complex of L² with monohydrogen phosphate provides direct evidence for the coordination mode of the anion. This "anion-coordination-induced emission" (ACIE) is another approach for fluorescence turn-on in addition to aggregation-induced emission (AIE). Phosphate ions in a bind: The tetrakis(bisurea)-decorated tetraphenylethene (TPE) displays fluorescence "turn-on" over a wide concentration range upon phosphate coordination. The fluorescence enhancement can be attributed to the restriction of the intramolecular rotation of TPE by anion coordination. This "anion-coordination-induced emission" (ACIE) is another approach for fluorescence turn-on.