Propriedades fotofísicas de complexos bis-heterolépticos de Ir(III) contendo o ligante 2-(2-piridil)benzimidazol e seus potenciais usos como biomarcadores

Abstract

In this work the [Ir(ppy)2(pbi)] (Ir1), [Ir(pq)2(pbi)] (Ir2) and [Ir(ppz)2(pbi)] (Ir3) complexes where ppy = 2 -phenylpyridine, pq = 2-phenylquinoline, ppz = 1-phenypyrazole, and pbi = 2-(2-pyridyl)benzimidazole were synthesized and characterized along with their respective conjugated acids [Ir(ppy)2(pbiH)]+ (Ir1-H), [Ir(pq)2(pbiH)]+, (Ir2-H), [Ir(ppz)2(pbiH)]+ (Ir3-H). The influence of the protonation of the imidazole site of the 2-(2-pyridyl)benzimidazole ligand on the photophysical and electrochemistry properties of the complexes was investigated in detail, evidencing a significant stabilization of the HOMO orbitals with the protonation of the imidazole group. The neutral complexes exhibit emission quantum yields (Φem) between 22 and 44% higher than their respective conjugated acids, which is justified by greater energetic separation between their triplets excited states as shown by TD-DFT calculations. Complementary low temperature emission experiments (77 K) allowed classifying the complexes according to the nature of their emitting state. The Ir1-H, Ir3-H and Ir3 complexes are grouped in the A system, which are characterized by having a 3MLCT state, while the Ir1, Ir2-H and Ir2-H complexes are grouped in the B system in which emission is mainly 3IL in character. The excited state lifetimes are significantly higher for 3IL emitters and revealed, together with temperature-dependent steady-state emission measurements (110 to 300 K) the existence of complex non-radiative processes for the systems studied in this work. Biomarking assays were performed to point out the potential use of the complexes as biomarkers. %uptake in HeLa cells ranged between 19 (Ir2) and 45% (Ir3). Flow cytometry assays showed cell staining above 70% of the cell population among all complexes. Additionally, no morphological changes are observed in the incubated cells, suggesting low cytotoxicity. Finally, confocal microscopy assays showed perinuclear labeling of all complexes distributed throughout the cytoplasm with potential specificity for labeling lysosomes.