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 lambda maxranges from 253 to 269 nm, with emissions from 357 to 365 nm. Calculations of the natural transition orbitals NTOs deliver the localized holeelectron 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 pi- and sigma-bonding contributions.