AcetylacetonateBODIPY−biscyclometalated Iridium(III) complexes: effective strategy towards smarte fluorescentphotosensitizer agents

Abstract

Biscyclometalated Ir(III) complexes involving BODIPYbased ancillary ligands, where the BODIPY unit is grafted to different chelating cores (acetylacetonate for Ir-1 and Ir-2, and bipyridine for Ir-3) by the BODIPY meso position, have been synthesized and characterized. Complexes having the BODIPY moiety directly grafted to acetylacetonate (Ir-1 and Ir-2) exhibit higher absorption coefficient (ca. ε = 4.46 104 M-1 cm-1 and 3.38 104 M-1cm-1 at 517 nm and 594 nm, respectively), higher moderate-fluorescence emission (ca. fl = 0.08 and 0.22 at 528 nm and 652 nm, respectively) and, especially, more efficient singlet oxygen generation upon visible-light irradiation (ca.  = 0.86 and 0.59, respectively) than that exhibited by Ir-3 (ca.  = 0.51, but only under UV light). Phosphorescence emission, nanosecond time-resolved transient absorption and DFT calculations suggest that BODIPY-localized long-lived 3IL states are populated for Ir-1 and Ir-2. In-vitro photodynamic therapy (PDT) activity studied for Ir-1 and Ir-2 in HeLa cells shows that such complexes are efficiently internalized into the cells, exhibiting low dark- and high photo-cytoxicity, even at significant low complex concentration, making them potentially suitable as theranostic agents.