posted on 2021-10-21, 16:34authored bySubhadeep Paul, Paramita Kundu, Paturu Kondaiah, Akhil R. Chakravarty
A series of multichromophoric ruthenium(II)
complexes with the
formulation [Ru(tpy-BODIPY)(tpy-R)]Cl2 (1–4), having a heteroleptic Ru(II)-bis-tpy (tpy = 4′-phenyl-2,2′:6′,2″-terpyridine)
moiety covalently linked to a boron-dipyrromethene (BODIPY) pendant,
have been prepared and characterized and their application as a phototherapeutic
and photodetection agent in cancer therapy has been explored. Ligand
L1 with a terpyridine-BODIPY moiety and complex 1 as its PF6 salt (1a) have been structurally
characterized by a single-crystal X-ray diffraction study. Complex 1a has a distorted-octahedral RuN6 core with a
Ru(II)-bis-terpyridine unit that is covalently linked to one photoactive
BODIPY unit. The complexes exhibit strong absorbance near 502 nm (ε
≈ (3.7–7.8) × 104 M–1 cm–1) and high singlet oxygen sensitization ability,
giving singlet oxygen quantum yield (ΦΔ) values
ranging from 0.57 to 0.75 in DMSO. An emission-based study using complex 4 and Singlet Oxygen Sensor Green (SOSG) displays the formation
of singlet oxygen inside the cells and also in the buffer medium upon
light irradiation. DNA (pUC19) photocleavage experiments using ROS
scavengers/stabilizers reveal photoinduced generation of singlet oxygen
by a type-II process and of the superoxide anion radical by a type-I
process. Complex 4 having a pendant biotin moiety as
a cancer cell targeting group shows high photocytotoxicity with a
remarkable phototherapeutic index (PI) value of >1400 in HeLa cancer
cells with a low light dose activation (400–700 nm, 2.2 J cm–2). The complexes display reduced activity in noncancerous
HPL1D cells. The emission property of the complexes is used for cellular
imaging, thus making them suitable as next-generation theranostic
PDT agents.