Homoleptic Bis(aryl)acenaphthenequinonediimine–Cu^I Complexes – Synthesis and Characterization of a Family of Compounds with Improved Light‐Gathering Characteristics

Abstract

A group of bis(aryl)acenaphthenequinonediimine (Ar‐BIAN) ligands were synthesized through a modified procedure, which bypasses the need for absolutely dry conditions during the initial template synthesis. The molecular and electronic structure of the corresponding homoleptic [Cu(Ar‐BIAN)2]BF4 complexes were probed by means of a variety of spectroscopic methods. In accord with solution 13C NMR spectra, X‐ray crystallography reveals D2 or approximate D2 symmetry for the [Cu(p‐Cl‐BIAN)2]+ and [Cu(p‐Me‐BIAN)2]+ cations and noncrystallographic C2 symmetry for the [Cu(o‐Ph‐BIAN)2]+ cation. The structures of the p‐Cl‐, p‐Me, and o‐Ph‐BIAN complexes agree with the presence of ligands in their neutral form according to the lengths of the relevant C–C and C=N bonds of the organic skeleton. The concerted stereo–electronic effects of the substituents on the aryl rings affect the electron donor/acceptor capacities of the ligands and the structures of the complexes, as the study of the visible absorption spectra of the complexes indicates. The spectra of the complexes are dominated by intense and broad metal‐to‐ligand charge transfer (MLCT) bands that enter the near‐infrared (NIR) region. Additionally, electrochemical studies undertaken reveal several successive electron capture and release processes, which further manifest the redox versatility of the ligands.

Development of earth-abundant copper photosensitizers for artificial photosynthesis

“…To find out the oxidation state of both the metal and Ar-BIAN ligand, Tkachenko and co-workers carried out NMR spectroscopy and crystallographic analysis to verify the presence of a Cu I center and that the coordinated Ar-BIAN ligands were structurally similar to the neutral ones within acceptable experimental error. 38 The sharp peaks in the NMR spectra obtained suggest the absence of paramagnetic behavior. The structure shown in Figure 1.9 shows the Ar-BIAN ligands and the corresponding Cu I complexes that they synthesized.…”

“…37 Scheme 1.3 Schematic representation of the rapid interconversion between the two conformers. 38 Another factor influencing the chelation to the metal center is the substituent group on the imine as it affects the stereoelectronic tunability. 37b This is evident from a series of experiments performed by the Ragaini group to obtain the relative coordination strength of different chelating nitrogen ligands toward Pd 0 and Pd II .…”

“…The MLCT absorption of the complexes has λmax in the visible region between 580 and 610 nm. 38 They postulated that when MLCT transitions are low-lying, they result in amply long photoexcited lifetimes and potential emission from the complexes. 38 Subsequently, Zysman-Colman and group observed weak emission signals, which were previously unobserved in Ar-BIAN Ir complexes, after installing ester and carboxylate functionalities in their heteroleptic Ir complexes at the bay region of the acenaphthene (Figure 1.10).…”

“…38 They postulated that when MLCT transitions are low-lying, they result in amply long photoexcited lifetimes and potential emission from the complexes. 38 Subsequently, Zysman-Colman and group observed weak emission signals, which were previously unobserved in Ar-BIAN Ir complexes, after installing ester and carboxylate functionalities in their heteroleptic Ir complexes at the bay region of the acenaphthene (Figure 1.10). The electron-withdrawing substituents were initially installed to improve the π-accepting ability and better anchoring of the complexes for incorporation into DSSCs.…”

“…Molecular structures of the Ar-BIAN ligands and the corresponding Cu I complexes Papanikolaou et al synthesized and studied 38. …”