Iridium(III) coordination compounds based on organophosphorus ancillary ligands showing cytotoxicity against breast cancer cells and Fe(III) luminescent sensing

Three phosphorescent iridium(III) complexes consisting bis-diphosphine ligands were prepared and characterized by single-crystal XRD, CHN analysis, spectroscopic techniques, cyclic voltammetry, and DFT. The synthesized complexes were the three monomeric [Ir(ppy)2(L1)Cl] (1), [Ir(ppy)2(L2)]Cl (2) and [Ir(ppy)2(L3)]Cl (3) where L1 = bis-(diphenylphosphino)methane (dppm), L2 = bis-(diphenylphosphino)propane (dppp) and L3 = bis-(diphenylphosphino)benzene (dppbe). Complexes 1-3 gave an absorption band between 240 to 380 nm in both CH2Cl2 and DMSO, which is assigned as a charge transfer transition based on theoretical calculation. They showed a blue-green emission at 460-520 nm in DMSO with an absolute quantum efficiency of 0.013-0.046 at room temperature. The selective photo-induced electron transfer (PET) by Fe3+ in DMSO, was studied to obey the Rehm-Weller principle. The 1:1 binding soichiometry between 1-3 and Fe3+ was established by Job's plot. The binding constants (Ka) were determined using the Benesi-Hildebrand plot. All the complexes are extremely more potent than cisplatin for in vitro antiproliferative activity towards the human breast cancer cells, HCC1937, MCF-7, and MDA-MB-231. The values of IC50 were in the range of 0.077-0.485 μM, and 1 exhibited the most effective IC50 against MDA-MB-231 cell line, the triple-negative breast cancer cell. Their lipophilicities (log P) were also examined to explain the penetration ability of the studied complexes towards cell barriers, and transport to the molecular target.

Featuring long-lifetime deep-red emitting iridiumIII complexes with high colour purity: insights into the excited state dynamics from spectroscopic and theoretical perspectives

The significant attention drawn to IrIII-complexes in recent years has boosted the development of new compounds with advantageous photophysical features. However, obtaining IrIII deep-red-emitting complexes with long lived excited state, high colour purity and high quantum yield (Φ) remains a challenging task. To address this issue, this study reports the synthesis and photophysical investigation of three novel zwitterionic complexes, [Ir(C^N)2bqdc] (C^N = ppy, phq, and bzq), with ppy = 2-phenylpyridine (Ir-pb), phq = 2-phenylquinoline (Ir-qb), bzq = benzo[h]quinoline (Ir-bb), and bqdc = potassium 2,2'-biquinoline-4,4'-dicarboxylate. These complexes exhibit high quantum yields and long emission lifetimes with high colour purity in the deep-red region. The structural characterisation carried out by usual spectroscopic measurements supports the proposed structures, while the photophysical study unveiled the high contribution of the 3MLCT state to the hybrid emitter state, as endorsed by theoretical investigations. The desired correspondence between the calculations and the experimental data set affirmed the accuracy of the theoretical analysis, which enabled us to establish a relationship between the ground-to-excited-state geometry distortion and the lifetime through the nonradiative decay (knr). Furthermore, these newly synthesized complexes exhibit quenching in the presence of molecular oxygen. In deoxygenated DMSO solution the knr values halve, increasing the quantum yields (34.0, 10.6, and 26.6%) and the lifetimes (1.13, 1.11, and 1.72 μs), while leading to quite pure deep-red emission - CIE coordinates: (0.67, 0.33), (0.60, 0.40;), (0.65, 0.35) for Ir-pb, Ir-qb, and Ir-bb, respectively. These complexes display considerable potential for a wide range of applications, such as photodynamic therapy, due to their attractive photophysical properties, and are among the deep-red-emitting complexes reported in the literature with longer lifetimes and higher Φ.