Fluorescence behaviour of an anthracene–BODIPY system affected by spin states of a dioxolene–cobalt centre
Dioxolene cobalt complexes, [Co(L)(TPA)]PF6 (1) and [Co(L)(Me3TPA)]PF6 (2), were synthesized using a catechol with anthracene and boron-dipyrromethene (BODIPY), H2L, and tris(pyridin-2-ylmethyl)amine (TPA) or tris[(6-methylpyridin-2-yl)methyl]amine (Me3TPA) and characterised by UV-vis absorption, IR and NMR spectroscopy. Complexes 1 and 2 are a low-spin cobalt(III) catecholate form and a high-spin cobalt(II) semiquinonate form, respectively, in CH3CN at room temperature. The effect of the spin states of the dioxolene–cobalt centre on fluorescence was investigated in CH3CN at room temperature. The fluorescence intensity of 1 was clearly lower than that of 2, although both complexes showed weaker fluorescence compared with that of H2L. The difference in the intensity between 1 and 2 is mainly due to the enhancement of nonradiative decay processes based on the stronger metal–ligand interactions for the cobalt(III) catecholate form of 1 compared with the cobalt(II) semiquinonate form of 2.