Pentafluorophenyl-bis(2-phenylbenzothiazole) PtIV Derivatives: Optoelectronic and Biological Studies

Abstract

Luminescent complexes based on organic chromophores with late transition metals haveattracted a great interest due to their interesting applications in fields such as photocatalysis,biosensing, photosensitizers and optoelectronic devices. In particular, numerous studies havebeen published on cyclometalated d6 (RuII, OsII or IrIII) and d8 (PtII) systems, whereasluminescent PtIV complexes have received less attention.[1] Our group has recently publishedtwo series of neutral pentafluorophenylbis(cyclometalated) PtIV with Cl- or CN- as auxiliaryligands.[2] In this field, 2-arylbenzothiazole chromophores have been employed as ligands toform yellow-orange phosphorescent metal complexes and recent studies have alsodemonstrated promising antiproliferative activity.[3]In this communication, we present a series of luminescent mononuclear PtIV complexes,fac-[Pt(pbt)2(C6F5)L]n+ (pbt = 2-phenylbenzothiazole; L = 4-Mepy 1, pybt 2, 4,4’-bpy 3, bpe 4,bpyb 5, n = 1; OCOCF3, 6 n = 0), and a bimetallic complex fac-[{Pt(pbt)2(C6F5)}2(-bpyb)](PF6)2(7), in which the trans ligand to the C(pbt) is varied to modify the optical properties andlipophilicity. All complexes have been fully characterized and their structure confirmed by X-raydiffraction studies on 1, 4 and 6. Optical properties have been investigated in detail andsupported by DFT/TD-DFT theoretical calculations. 4 is not emissive due to a fastphotoisomerization process E/Z on the bpe ligand. The in-vitro antiproliferative activity ofselected compounds (1-3 and 6) against two human tumor cell lines (A549 and HeLa) and theirselectivity index against the non-tumor cell line BEAS-2B were examined. Cationic complexes1-3 exhibit IC50 values in the nanomolar range, revealing an encouraging antineoplastic activity,whereas the neutral complex 6 shows low cytotoxicity in the dark and high photocytotoxicity byshort irradiation with blue light