The synthesis of the asymmetric ligand 3phenyl-1-(pyridin-2-yl)-1H-pyrazol-5-amine (L1) and its single-crystal X-ray structure are reported. L1 displays crystallographic symmetry (orthorhombic, Pccn) higher than its molecular symmetry (point group C 1 ) and also displays supercooling, with a difference in the melting and solidification points of over 100 °C. Upon complexation with ZnCl 2 , L1 engages in both primary cation and secondary anion coordination via hydrogen bonding, and the complex exhibits a room-to-low-temperature single crystal-to-crystal phase transition. The ZnCl 2 complex becomes a birefringent fluid mixed with crystalline domains at high temperatures, as detected by polarized optical microscopy. Examination of the photoluminescence properties showed that the emission intensity increased and a pronounced bathochromic shift was observed in the emission maximum upon going from solution to the solid state, for both the ligand and complex, consistent with aggregation-induced emission behavior.

The synthesis and single crystal structures of 3-phenyl-1-(pyridin-2-yl)-1<i>H</i>-pyrazol-5-amine (<b>L1</b>) and its complex with ZnCl₂are reported. <b>L1</b> exhibits supercooling, with a difference in melting and solidification points of over 100 ^oC. The complex [<b>L1</b>ZnCl₂] has a room-to-low temperature single crystal-to-crystal phase transition in the solid state, while a birefringent fluid phase mixed with crystalline domains is observed at high temperatures. Significant fluorescence enhancement is observed upon formation of the ZnCl₂ complex.

The synthesis and single crystal structures of 3-phenyl-1-(pyridin-2-yl)-1<i>H</i>-pyrazol-5-amine (<b>L1</b>) and its complex with ZnCl₂are reported. <b>L1</b> exhibits supercooling, with a difference in melting and solidification points of over 100 ^oC. The complex [<b>L1</b>ZnCl₂] has a room-to-low temperature single crystal-to-crystal phase transition in the solid state, while a birefringent fluid phase mixed with crystalline domains is observed at high temperatures. Significant fluorescence enhancement is observed upon formation of the ZnCl₂ complex.