Cancers treated by chemotherapy use reagents such as cisplatin. Cisplatin, cis-[PtII(NH3)2Cl2], a square planar, Pt(II) metal complex terminates cancer cells after undergoing a thermal hydrolysis in solution that activates covalent binding to DNA. Cisplatin is problematic in differentiating healthy cells from cancer cells and targets them indiscriminately causing side effects such as ototoxicity and nephrotoxicity. Photodynamic therapy uses the photochemical properties of chemical reagents to selectively target cancer cells using visible light. Most photodynamic therapeutics are oxygen dependent and cannot effectively treat tumors in hypoxic environments. The research aims to reduce oxygen dependency using Rh(III) polypyridyl complexes’ photochemical properties. When irradiated with UV light, cis-[RhIII(NN)2Cl2]+ complexes (NN=bidentate polypyridyl ligand) can photodissociate chloride and covalently bind to DNA, but UV light damages tissue. To make the cis-[RhIII(NN)2Cl2]+ complexes more visible light active, a BODIPY fluorophore is coupled to the Rh(III) metal center. BODIPY is a very emissive fluorophore which absorbs visible light strongly and can undergo excited state electron transfer. The research will discuss the photophysical and electrochemical properties of a new visible light active Rh-BODIPY complex. The coupling of BODIPY to Rh(III) greatly expands the electronic absorbance into the visible region. A cyclic voltammogram of the Rh-BODIPY complex shows a BODIPY-based HOMO and a Rh(III)-based LUMO. Fluorescence quenching is observed using emission spectroscopy upon coordination of the BODIPY to Rh(III). Upon irradiation using 532 nm light (green light), it is observed that the BODIPY π→π* transition at 529 nm decreases. Using spectroelectrochemistry, a similar decrease is observed upon BODIPY oxidation. This supports photo-oxidation of BODIPY upon irradiation with visible light. It is hypothesized that an excited state electron transfer can occur from the BODIPY-based HOMO to the Rh(III)-based LUMO to photodissociate chloride and bind to DNA as a possible new phototherapeutic.

Photophysical and photochemical properties of Rh(III)-BODIPY polypyridyl complexes

ACS Fall 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.