Re-arrangements of 4-[(4H-1,2,4-triazol-4-ylimino)methyl]phenol with different inorganic anions: Crystal structure and fluorescence properties

Abstract

Fluorescent materials have many interesting applications, but it remains difficult to control the luminescence of organic materials and in particular to retain the same luminescence in solution and in the solid state, a property of interest for various imaging applications. In this work, the influence of inorganic-anions on the crystal structure and physical–chemical properties of a series organic salts L+Cl− (1), L+ClO4− (2), L+NO3−·H2O (3), 2L+SO42−·2H2O (4) (L=4-[(4H-1,2,4-triazol-4-ylimino)methyl]phenol) has been investigated. Single crystal X-ray analyzes revealed that salt 1 formed a linear structure connected by H⋯O interactions, while salts 2–4 all formed 2D network structures through O⋯O interactions. The protonated L+s adopt face-to-face slipped π-stacked arrangement in salts 1 and 3, while display monomer arrangements in 2 and 4, the latter can be attribute to the entrapment of heavy anions in the crystal lattices. Optical-properties measurements of these four salts have shown L+ arrangements dependent on solid-state properties: salt 1 and 3 show broad emission bands (λ1=478nm, λ2=487nm) with a red shift of about 60nm relative to its fluorescence in solvents, while 2 and 4 are similar to each other, exhibiting sharp bands (λ3=453nm, λ2=433nm) with the higher ϕPL values (ϕPL1=0.08, ϕPL1=0.15, ϕPL1=0.06, ϕPL1=0.14). These results demonstrated the significant influence of inorganic-anions on the organic salts and the optical properties of organic materials could be modulated by entrapping different anions in lattice.