X-shaped π-conjugated fluorophores enable cooperative ion-pair recognition with multicolour emission

Abstract

An X-shaped π-conjugated molecule (X1) incorporating orthogonal cation- and anion-recognition sites, azacrown ethers and dimesitylborane units, respectively, was synthesised and compared with two linear analogues (L1 and L2). UV/Vis absorption and fluorescence titration experiments revealed that X1 undergoes stepwise binding of both CN⁻ and K⁺ ions, accompanied by distinct spectral changes. Binding constants determined from non-linear fitting, together with electrostatic potential calculations, demonstrated negative cooperativity for homo-ion binding, and the sequential binding of CN⁻ and K⁺ ions induced positive hetero-ion cooperativity. The spatially separated architecture of X1 allows independent modulation of HOMO and LUMO orbitals, leading to multicolour photoluminescence. Notably, all X1 ion complexes retained high photluminscence quantum yields (>25%), unlike the linear analogues, highlighting its potential as a modular platform for selective and responsive ion-pair sensing.