Cross-Coupled Phenyl- and Alkynyl-Based Phenanthrolines and Their Effect on the Photophysical and Electrochemical Properties of Heteroleptic Cu(I) Photosensitizers

Abstract

With the aims of increasing the antenna system and improving the photophysical properties of Cu(I)-based photosensitizers, the backbone of 2,9-dimethyl-1,10-phenanthroline was selectively extended in the 5,6-position. Applying specifically tailored Suzuki−Miyaura and "chemistry-on-the-complex" Sonogashira cross-coupling reactions enabled the development of two sets of structurally related diimine ligands with a broad variety of different phenyl-and alkynyl-based substituents. The resulting 11 novel heteroleptic Cu(I) complexes, including five solid-state structures, were studied with respect to their structure− property relationships. Both sets of substituents are able to red-shift the absorption maxima and to increase the absorptivity. For the alkynyl-based complexes, this is accompanied by a significant anodic shift of the reduction potentials. The phenyl-based substituents strongly influence the emission wavelength and quantum yield of the resulting Cu(I) complexes and lead to an increase in the emission lifetime of up to 504 ns, which clearly indicates competition with the benchmark system [(xantphos)Cu(bathocuproine)]PF 6 .

How the Way a Naphthalimide Unit is Implemented Affects the Photophysical and -catalytic Properties of Cu(I) Photosensitizers

“…Similar observations were made for Cubiipo (Argüello and other asymmetrically substituted [(xant)Cu(diimine)] + complexes (Schmid et al, 2018). This in strong contrast to the commonly observed single signal at around 1.7-1.8 ppm for the two methyl groups (s, 6H, CH 3 ) in related symmetrically substituted Cu(I) complexes (Luo et al, 2013;Mejía et al, 2013;Kim et al, 2017;Doettinger et al, 2021) and is also in contrast to the unsubstituted Cuphen complex (1.76 ppm, s, 6H, CH 3 ) (Supplementary Figure S7). The same splitting phenomenon can also be seen in the 13 C NMR spectra of CuNIphen and Cubiipo.…”

“…As a consequence of their limited absorptivity in the visible region, numerous efforts have been made to modify and to adjust the diimine ligand. For example, several phenanthroline derivatives bearing phenyl and alkynyl substituents (Mejía et al, 2013;Chen et al, 2017;Kim et al, 2017;Zhang et al, 2018a;Doettinger et al, 2021;Forero Cortés et al, 2021) or (diaza)anthracene (Heberle et al, 2017;Soulis et al, 2018;Giereth et al, 2019) moieties were explored, but with limited success. Therefore, in some other studies naphthalene imides were applied as a promising alternative (Tyson et al, 2001;Yarnell et al, 2011;Castellano, 2015;Argüello Cordero et al, 2022).…”

Closo- or Nido-Carborane Diphosphane as Responsible for Strong Thermochromism or Time Activated Delayed Fluorescence (TADF) in [Cu(N^N)(P^P)]0/+

“…The synthesis and study of heteroleptic copper complexes [Cu­(N^N)­(P^P)] n ( n = 0, 1) represents a growing field in the study of emissive coordination complexes. − One evident reason is the use of a cheaper metal (Cu) compared to those widely selected for the design of phosphors for emissive devices, such as Ir, Pt, or Au. Another relevant reason is related to their composition, which combines a diimine and a diphosphane.…”

Pyrimidoquinxoalinophenanthroline opens next chapter in design of bridging ligands for artificial photosynthesis

“…[27] Only few articles integrate acceptor-substituted phenyl compounds because monosubstitution and/or dehalogenation reactions hamper those synthetic pathways. [28] Especially, cross-coupling with electron-deficient nitrogen heterocycles proves to be challenging. [29][30][31] Published reaction conditions for Stille cross-coupling yielded exclusively in mono-substitution and concomitant dehalogenation of the second halogen substituent.…”

“…The range of the observed torsion angels is in accordance to other σv symmetric systems reported in literature. [28] Medium steric hinderance produced by the x protons (recall Figure 1) of the pyrimidine rings yields less tilted geometries than observed for higher sterically crowded substituents. [32] Hydrogen bonding of one of the pyrimidine nitrogen atoms of Rudpymp towards co-crystallized water (1.884 Å) may affect this as well.…”