Photodynamic therapy applications of Re(I)‐BODIPY functionalized nanoparticles

Abstract

Organometallic Re(I)‐BODIPY compounds have recently received attention as metal‐based photosensitizers for photodynamic therapy (PDT) applications owing to their strong absorption in the visible region. We synthesized and characterized an organometallic [ReI(L)2(CO)3Br] (ReL) complex containing a BODIPY ligand (L) and prepared nanoparticles of the ligand (NPL) as well as the complex (NPReL). The formation of nanoparticles was confirmed by dynamic light scattering (DLS), atomic force microscopy (AFM), transmission electron microscopy (TEM), and energy dispersive X‐ray (EDX) analyses. Single‐crystal structure of ReL showed octahedral environment around Re center, and the BODIPY chromophore was placed at distances of around 12 Å. Detailed photophysical properties of ReL were investigated which showed strong visible absorption at 551 nm (ε = 1.46 × 105 M−1 cm−1) owing to π‐conjugation of BODIPY with the metal center Re(I). Efficient intersystem crossing (ISC) and formation of triplet‐excited states with lifetimes of 0.80 and 0.65 μs for L and ReL, respectively, were confirmed through nanosecond‐laser flash photolysis and density functional theory (DFT) calculations. The photosensitization efficiency of ReL was observed to be ϕΔ = 0.77. In vitro biological studies of NPReL showed negligible toxicity and reactive oxygen species (ROS) generation in the dark as compared with NPL despite the good photosensitization ability of NPL. Therefore, NPReL showed coordination‐enhanced cytotoxicity under irradiation conditions and interestingly found to be nontoxic to normal NIH3T3 cell lines in comparison with L. Flow cytometry studies further indicated that the major cause of cell death by NPReL was via apoptotic pathways (54%), which authenticates its potential as a PDT agent.