4′–phenyl −2, 2′: 6′, 2′’-terpyridine derivatives as metal chemosensors. Chelation and fluorescence capabilities towards Zn(II), Cd(II), and Hg(II) from experiment and theory

4′-phenylterpyridine (TPY) involves four conjugated rings, leading to a multi-resonant chromophore with exceptional luminescent features. Further functionalization of the 4′-phenyl moiety enables a versatile set of chemosensors. In the series, the optical transitions remain similar, where λ_max ranges from 253 to 269 nm, with emissions from 357 to 365 nm. Calculations of the natural transition orbitals NTOs deliver the localized hole-electron densities, indicating that the electronic transitions vary as a local-excitation (LE), charge transfer (CT), and mixed LE-CT along with the set. We employ the energy decomposition analysis to evaluate the possible coordination toward Zn(II), Cd(II), and Hg(II) cations, showing a favorable formation of complexes, where the interaction nature exhibits a ∼ 49 and ∼ 50 % electrostatic and orbital character for the Zn(II), Cd(II) and Hg(II) centers. Furthermore, the density deformation channels confer an explicit picture of the bonding scheme, denoting π- and σ-bonding contributions.