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Ir(III) and Ru(II) polypyridyl complexes are promising photosensitizers (PSs) for photodynamic therapy (PDT) due to their outstanding photophysical properties. Herein, one series of cyclometallated Ir(III) complexes and two series of Ru(II) polypyridyl derivatives bearing three different thiazolyl-β-carboline N^N' ligands have been synthesized, aiming to evaluate the impact of the different metal fragments ([Ir(C^N) 2 ] + or [Ru(N^N) 2 ] 2+ ) and N^N' ligands on the photophysical and biological properties. All the compounds exhibit remarkable photostability under blue-light irradiation and are emissive (605 < λ em  < 720 nm), with the Ru(II) derivatives displaying higher photoluminescence quantum yields and longer excited state lifetimes. The Ir PSs display pK a values between 5.9 and 7.9, whereas their Ru counterparts are less acidic (pK a > 9.3). The presence of the deprotonated form in the Ir-PSs favours the generation of reactive oxygen species (ROS) since, according to theoretical calculations, it features a low-lying ligand-centered triplet excited state (T 1  =  3 LC) with a long lifetime. All compounds have demonstrated anticancer activity. Ir(III) complexes 1-3 exhibit the highest cytotoxicity in dark conditions, comparable to cisplatin. Their activity is notably enhanced by blue-light irradiation, resulting in nanomolar IC 50 values and phototoxicity indexes (PIs) between 70 and 201 in different cancer cell lines. The Ir(III) PSs are also activated by green (with PI between 16 and 19.2) and red light in the case of complex 3 (PI = 8.5). Their antitumor efficacy is confirmed by clonogenic assays and using spheroid models. The Ir(III) complexes rapidly enter cells, accumulating in mitochondria and lysosomes. Upon photoactivation, they generate ROS, leading to mitochondrial dysfunction and lysosomal damage and ultimately cell apoptosis. Additionally, they inhibit cancer cell migration, a crucial step in metastasis. In contrast, Ru(II) complex 6 exhibits moderate mitochondrial activity. Overall, Ir(III) complexes 1-3 show potential for selective light-controlled cancer treatment, providing an alternative mechanism to chemotherapy and the ability to inhibit lethal cancer cell dissemination., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Masson SAS.. All rights reserved.)

The theoretical calculation of the temperature-dependent nonradiative decay rate constant is fundamental for predicting the usefulness of transition-metal complexes for technological applications. Such a computation implies the determination of the barriers separating the emitting triplet state from metal-centered states, which are key mediators of this type of radiationless relaxation. We here do so for the two green-emitting cyclometalated Ir(III) complexes, [Ir(ppy) 2 (pyim)] + and [Ir(diFppy) 2 (dtb-bpy)] + , of general formula [Ir(C ∧ N) 2 (N ∧ N)] + , performing DFT calculations with both B3LYP and PBE0 functionals. On the basis of the obtained results and the comparison with the experimental nonradiative decay rate constants, we conclude that B3LYP provides too low energy barriers to the metal-centered states, while the PBE0 provides reasonable values. We consequently recommend to avoid the use of the commonly employed B3LYP functional for the evaluation of such an energy barrier for cyclometalated Ir(III) complexes.

Donor-acceptor-substituted biphenyl derivatives are particularly interesting model compounds, which exhibit intramolecular charge transfer because of the extent of charge transfer between both substituents. The connection of a 4-[1,1'-biphenyl]-4-yl-2-pyrimidinyl) moiety to differently disubstituted amino groups at the biphenyl terminal can offer push-pull compounds with distinctive photophysical properties. Herein, we report a comprehensive study of the influence of the torsion angle of the disubstituted amino group on the emissive properties of two pull-push systems: 4-[4-(4- N , N -dimethylaminophenyl)phenyl]-2,6-diphenylpyrimidine ( D1 ) and 4-[4-(4- N , N -diphenylaminophenyl)phenyl]-2,6-diphenylpyrimidine ( D2 ). The torsion angle of the disubstituted amino group, either N , N -dimethyl-amine or N , N -diphenyl-amine, at the biphenyl end governs their emissive properties. A drastic fluorescence quenching occurs in D1 as the solvent polarity increases, whereas D2 maintains its emission independently of the solvent polarity. Theoretical calculations on D1 support the presence of a twisted geometry for the lowest energy, charge-transfer excited state (S 1,90 ), which corresponds to the minimum energy structure in polar solvents and presents a small energy barrier to move from the excited to the ground state, thereby favoring the non-radiative pathway and reducing the fluorescence efficiency. In contrast, this twisted structure is absent in D2 due to the steric hindrance of the phenyl groups attached to the amine group, making the non-radiative decay less favorable. Our findings provide insights into the crucial role of the substituent in the donor moiety of donor-acceptor systems on both the singlet excited state and the intramolecular charge-transfer process., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Cortés-Villena, Soriano-Díaz, Domínguez, Vidal, Rojas, Aliaga, Giussani, Doménech-Carbó, Ortí, Galian and Pérez-Prieto.)

In the present contribution, the following three cyclometallated Ir(III) complexes were theoretically investigated using density functional theory calculations to explain their different photophysical properties: [Ir(ppy) 2 (bpy)] + , where Hppy is 2-phenylpyridine and bpy is 2,2'-bipyridine, [Ir(ppy) 2 (pbpy)] + , where pbpy is 6-phenyl-2,2'-bipyridine, and [Ir(ppy) 2 (dpbpy)] + , where dpbpy is 6,6'-diphenyl-2,2'-bipyridine. Despite sharing the same molecular skeleton, with the only difference being the addition of one or two phenyl groups attached to the ancillary bpy ligand, the complexes show different emission quantum yields in CH 2 Cl 2 solution (0.196, 0.049 and 0.036, respectively). Such a behavior was previously justified as a consequence of a different ability to non-radiatively decay through an axial metal-centered (MC) triplet state. In the present contribution, a new non-radiative decay path has been characterized to be mediated by the so-called equatorial MC states, in which an Ir-N bpy bond is elongated instead of an Ir-N ppy bond as observed in the axial MC states. The decay path involving the equatorial MC states is more favorable than that associated with the axial MC states, and the different ability to decay through the former better explains the photoemission properties exhibited by the three complexes.

The outbreak of viral infectious diseases urges airborne droplet and surface disinfection strategies, which may rely on photocatalytic semiconductors. A lipid bilayer membrane generally encloses coronaviruses and promotes the anchoring on the semiconductor surface, where, upon photon absorption, electron-hole pairs are produced, which can react with adsorbed oxygen-containing species and lead to the formation of reactive oxygen species (ROSs). The photogenerated ROSs may support the disruptive oxidation of the lipidic membrane and pathogen death. Density functional theory calculations are employed to investigate adsorption modes, energetics, and electronic structure of a reference phospholipid on anatase TiO 2 nanoparticles. The phospholipid covalently bound on TiO 2 , engaging a stronger adsorption on the (101) than on the (001) surface. The energetically most stable structure involves the formation of four covalent bonds through phosphate and carbonyl oxygen atoms. The adsorbates show a reduction of the band gap compared with standalone TiO 2 , suggesting a significant interfacial coupling.

The photophysical behavior of the cyclometalating Ir(III) complexes [Ir(ppy) 2 (bpy)] + , where Hppy is 2-phenylpyridine and bpy is 2,2'-bipyridine (complex 1 ), and [Ir(diFppy) 2 (dtb-bpy)] + , where diFppy is 2-(2,4-difluorophenyl)pyridine and dtb-bpy is 4,4'-di- tert -butyl-2,2'-bipyridine (complex 2 ), has been theoretically investigated by performing density functional theory calculations. The two complexes share the same molecular skeleton, complex 2 being derived from complex 1 through the addition of fluoro and tert -butyl substituents, but present notable differences in their photophysical properties. The remarkable difference in their emission quantum yields (0.196 for complex 1 in dichloromethane and 0.71 for complex 2 in acetonitrile) has been evaluated by characterizing both radiative and nonradiative decay paths. It has emerged that the probability of decaying through the nonradiative triplet metal-centered state, normally associated with the loss of the emission quantum yield, does not appear to be the reason behind the reported substantially different emission efficiency. A more critical factor appears to be the ability of complex 2 to emit from both the usual metal-to-ligand charge-transfer state and from two additional ligand-centered states, as supported by the fact that the respective minima belong to the potential energy surface of the lowest triplet T 1 state and that their phosphorescence lifetimes are in the same order of magnitude. In contrast, the emission of complex 1 can be originated only from the metal-to-ligand charge-transfer state, being the only emissive T 1 minimum. The results constitute a significant case in which the emission from ligand-centered states is the key for determining the high emission quantum yield of a complex.