Cobalt­(III) complexes [Co­(TPA)­(L1)]­(ClO4)2 (1), [Co­(4-COOH-TPA)­(L1)]­(ClO4)2 (2), [Co­(TPA)­(L2)]­Cl2 (3), and [Co­(4-COOH-TPA)­(L2)]­Cl2 (4) having acetylacetonate-linked boron-dipyrromethene ligands (L 1 , acac-BODIPY; L 2 , acac-diiodo-BODIPY) were prepared and characterized, and their utility as bioimaging and phototherapeutic agents was evaluated (TPA, tris-(2-pyridylmethyl)­amine; 4-COOH-TPA, 2-((bis-(2-pyridylmethyl)­amino)­methyl)­isonicotinic acid). HL 1 , HL 2 , and complex 1 were structurally characterized by X-ray crystallography. Complexes 1 and 2 on photoactivation or in a reducing environment (excess GSH, ascorbic acid, and 3-mercaptopropionic acid) released the acac-BODIPY ligand. They exhibited strong absorbance near 501 nm (ε ∼ (5.2–5.8) × 104 M–1 cm–1) and emission bands near 513 nm (ΦF ∼ 0.13, λex = 490 nm) in dimethyl sulfoxide (DMSO). Complexes 3 and 4 with absorption maxima at ∼536 and ∼538 nm (ε ∼ (1.2–1.8) × 104 M–1 cm–1), respectively, afforded high singlet oxygen quantum yield (ΦΔ ∼ 0.79) in DMSO. Complexes 1–4 showed Co­(III)–Co­(II) redox responses near −0.2 V versus saturated calomel electrode (SCE) in dimethylformamide (DMF)–0.1 M tetrabutylammonium perchlorate (TBAP). The photocleavage of pUC19 DNA by complex 4 revealed the formation of both singlet oxygen and superoxide anion radicals as the reactive oxygen species (ROS). Confocal fluorescence microscopy showed the selective accumulation of complex 1 in the endoplasmic reticulum (ER) in A-549 cells. Complex 4 exhibited a high phototherapeutic index value (PI > 7000) in HeLa cancer cells (IC50 ∼ 0.007 μM in visible light of 400–700 nm, total dose ∼5 J cm–2). The ancillary ligands in the complexes demonstrated a structure–activity relationship and modulated the Co­(III)–Co­(II) redox potential, the complex solubility, acac-BODIPY ligand release kinetics, and phototherapeutic efficacy.

We found an error in Fig. 6 showing similarity among few lanes of the gel diagram. The earlier image has been replaced with the corrected one which is given below. This correction does not change the conclusions of the article. The authors would like to apologise for any inconvenience caused.

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