Multidentate Phenanthroline Ligands Containing Additional Donor Moieties and Their Resulting Cu(I) and Ru(II) Photosensitizers: A Comparative Study

Abstract

To bind or not to bind: Driven by the motivation to increase the (photo)stability of traditional Cu(I) photosensitizers, multidentate diimine ligands, which contain two additional donor sites, were designed. To this end, a systematic series of four 1,10phenanthroline ligands with either OR or SR (R = i Pr or Ph) donor groups at the 2 and 9 positions and their resulting hetero-and homoleptic Cu(I) complexes were prepared. In addition, the related Ru(II) complexes were also synthesized to study the effect of another metal center. In the following, a combination of NMR spectroscopy and X-ray analysis was used to evaluate the impact of the additional donor moieties on the coordination behavior. Most remarkably, for the homoleptic bis(diimine)copper(I) complexes, a pentacoordinated copper center, corresponding to a (4 + 1)-fold coordination mode, was found in the solid state. This additional binding is the first indication that the extra donor might also occupy a free coordination site in the excited-state complex, modifying the nature of the excited states and their respective deactivation processes. Therefore, the electrochemical and photophysical properties of all novel complexes (in total 13) were studied in detail to assess the potential of these photosensitizers for future applications within solar energy conversion schemes. Finally, the photostabilities and a potential degradation mechanism were analyzed for representative samples.

Photostable Ruthenium(II) Isocyanoborato Luminophores and Their Use in Energy Transfer and Photoredox Catalysis

“… 24 − 26 Against this background, the development of ruthenium(II)- and iridium(III)-based photosensitizers continues to be important. 27 − 46 …”

The surprising effects of sulfur: achieving long excited-state lifetimes in heteroleptic copper(i) emitters

“…In line with our observations, Rentschler et al recently reported a series of [Cu(xantphos)(N^N)] + complexes in which the N^N ligands were 2,9-(RSCH 2 )-phen (R = phenyl or iso-propyl) but the authors did not report any intense absorption bands between 300 and 400 nm, despite the substituent containing a sulfur atom. 12 Excitation into the absorption bands around 400 nm of the [Cu(P^P)(N^N)] + complexes in deaerated solutions of THF or CH 2 Cl 2 at 293 K leads to luminescence (Fig. 5, S65-S67 and Table 3).…”

“…Light-emitting electrochemical cells (LECs) are devices for solidstate lighting, which were first described in 1995. 12 In these devices, a polymer (PLEC) or ionic transition metal complex (iTMC-LEC) is employed as a luminescent compound. Traditionally, iridium(III) and ruthenium(II) complexes have been used in iTMC-LECs due to their colour tunability (especially for Ir) and because their large spin-orbit coupling (SOC) leads to the mixing of singlet and triplet excited-states, thereby allowing for singlet as well as triplet exciton-harvesting.…”

“…Although the spin-orbit coupling of copper is rather small compared to that of the heavier d-block metals, there are several examples of heteroleptic [Cu(P^P)(N^N)] + complexes with high photoluminescence quantum yields (PLQYs). [10][11][12] This is attributed to thermallyactivated delayed fluorescence (TADF), a phenomenon in which the energy separation of the excited singlet (S 1 ) and excited triplet (T 1 ) states is very small, permitting reverse intersystem crossing to repopulate the S 1 state from the T 1 state at room temperature. 13 The most commonly used ligands in mononuclear heteroleptic [Cu(P^P)(N^N)] + complexes are POP (bis(2-(diphenylphosphano)phenyl)ether) or xantphos (4,5-bis(diphenylphosphano)-9,9dimethylxanthene) (Scheme 1) as the bis(phosphane) P^P, and bpy or phen derivatives as the N^N ligands.…”

Designing luminescent diimine-Cu(i)–phosphine complexes by tuning N-ligand and counteranions: correlation of weak interactions, luminescence and THz absorption spectra

“…For tetrahedral diimine-Cu(I)-phosphine complex system, the emission state usually has a metal-toligand charge transfer (MLCT) characteristic, which is sensitive to the coordination environment. 7,8 In general, the excited state geometry is susceptible to Jahn-Teller geometric distortion and becomes a flattened conformation, facilitating relaxation to ground state through non-radiative decay pathways. 9 In general, the structural modification of common organic ligands such as phen or the design of new ligands are considered to be the most important methods for the synthesis of Cu(I) luminescent complexes.…”