Bichromophoric Photosensitizers: How and Where to Attach Pyrene Moieties to Phenanthroline to Generate Copper(I) Complexes

Abstract

Pyrene is a polycyclic aromatic hydrocarbon and organic dye that can form superior bichromophoric systems when combined with a transition metal-based chromophore. However, little is known about the effect of the type of attachment (i.e., 1- vs 2-pyrenyl) and the individual position of the pyrenyl substituents at the ligand. Therefore, a systematic series of three novel diimine ligands and their respective heteroleptic diimine-diphosphine copper(I) complexes has been designed and extensively studied. Special attention was given to two different substitution strategies: (i) attaching pyrene via its 1-position, which occurs most frequently in the literature, or via its 2-position and (ii) targeting two contrasting substitution patterns at the 1,10-phenanthroline ligand, i.e., the 5,6- and the 4,7-position. In the applied spectroscopic, electrochemical, and theoretical methods (UV/vis, emission, time-resolved luminescence and transient absorption, cyclic voltammetry, density functional theory), it has been shown that the precise choice of the derivatization sites is crucial. Substituting the pyridine rings of phenanthroline in the 4,7-position with the 1-pyrenyl moiety has the strongest impact on the bichromophore. This approach results in the most anodically shifted reduction potential and a drastic increase in the excited state lifetime by more than two orders of magnitude. In addition, it enables the highest singlet oxygen quantum yield of 96% and the most beneficial activity in the photocatalytic oxidation of 1,5-dihydroxy-naphthalene.

Cu(ii) flavonoids as potential photochemotherapeutic agents

“…5,9 In this context, the significance of copper complexes should be noted due to their participation in vital biological functions and relatively modest toxicity in comparison to other heavy metals. [16][17][18] Moreover, these complexes exhibit anticancer properties attributed to their photo-redox activity, enabling them to produce cytotoxic reactive oxygen species (ROS). 19 Although the primary responsibility of incorporating free Cu(II) ions into cells lies with the copper transporter hCTR1, it is passive diffusion that predominantly accounts for the absorption of Cu(II) complexes.…”

Enhanced Visible Light Absorption in Heteroleptic Cuprous Phenanthrolines

“…Two classes of Cu­(I) bis -phenanthrolines engender either homoleptic or heteroleptic ligand topologies. Homoleptic cuprous phenanthrolines have been studied since the 1970s for their potent photoreducing capabilities, long-lived excited states, and tremendous durability to high-power laser excitation. ,,− Heteroleptic complexes using diimine- and bis -phosphine-type ligands have been growing in interest, especially for applications in dye-sensitized solar cells, − photoredox catalysis, − and the construction of supramolecular donor–acceptor architectures. ,,− The HETPHEN strategy leverages 2,9-mesityl-1,10-phenanthroline (mesPhen), ,, which is unable to form a bis -homoleptic complex but enables the binding of another suitable phenanthroline, assisted through π-interactions with the 2,9-mesityl substituents and the B-ring of the orthogonally coordinated phenanthroline. This platform facilitates a facile pathway for obtaining heteroleptic Cu­(I) complexes with the generic formula [Cu­(mesPhen)­(L)] + , where L is a second and distinct phenanthroline ligand (Chart ).…”

Controlling Excited State Localization in Bichromophoric Photosensitizers via the Bridging Group

“…One means by which this can be achieved is through the incorporation of large aromatic chromophores. This can facilitate a population of triplet ligand-centered ( 3 LC) states, which typically have much longer lifetimes than their triplet metal-to-ligand charge-transfer ( 3 MLCT) state counterparts due to their localization away from the metal center. ,,− For example, a recent study by Choroba et al investigated pyrene-substituted Re­(I) complexes with room-temperature phosphorescent lifetimes greater than 1000 μs . Similarly, a study by Wenger and co-workers showed that naphthalene was able to function as a triplet reservoir in an Ir­(III) complex, leading to lifetimes of 72.1 μs .…”