Construction of SCO-fluorescence bifunctional cobalt(ii) complexes with anthracene-decorated terpy ligands

Abstract

The development of bifunctional materials integrating spin-crossover (SCO) and fluorescence properties has attracted increasing attention. However, no reports have thus far described Co(II)-based SCO systems exhibiting such dual functionality. In this study, we designed a terpyridine ligand incorporating an anthracene-decorated fluorophore, 4′-(anthracen-9-yl)-4,4″-dimethyl-2,2′:6′,2″-terpyridine (L), and synthesized three mononuclear Co(II) complexes: [Co(L)₂](BF₄)₂·Et₂O·0.8CH₃OH·H₂O (1), [Co(L)₂]Br₂·3DMF (2) and [Co(L)₂](ClO₄)₂·0.5H₂O (3). Magnetic susceptibility measurements revealed that all three complexes exhibit incomplete SCO behavior. Variable-temperature fluorescence spectroscopy demonstrated the coexistence of SCO and fluorescence in these systems. The intramolecular luminescence emission characteristics were further elucidated through variable-temperature UV-vis absorption spectroscopy and time-dependent density functional theory calculations. This work expands the system of bifunctional SCO-fluorescent materials and provides valuable insights into the design of multifunctional molecular systems.