Di- and tetranuclear transition metal complexes of a tetrakisguanidino-substituted phenazine dye by stepwise coordination

Abstract

2,3-Bis- and 2,3,7,8-tetrakisguanidino-substituted phenazines are intensely-coloured dyes that offer two different sites for metal coordination or benzylation, namely the imino nitrogen atoms of the guanidino groups and the phenazine nitrogen atoms. In this work, sequential coordination at both sites is studied, and the effects on the electronic structure and optical properties are analyzed. The step-wise coordination is used to synthesize tetranuclear mixed-valence (CuI)2(CuII)2 and heterobimetallic Cu2Ni2 complexes. Coordination at the guanidino groups switches on a ligand-metal charge-transfer character of electronic transitions in the visible region, leading to a massive intensity gain in the case of copper coordination. The second coordination step with CuI takes place at the phenazine nitrogen atoms and further decreases the ligand frontier orbitals. In the case of two tricoordinated CuI atoms in the product complex, the charge-transfer character of the electronic excitation vanishes, while their energies are very similar. On the other hand, for CuI atoms with a coordination number of only 2, the stronger Cu-N bond leads to a red-shift of the electronic transitions.

Hydrogen bonds and dispersion forces serving as molecular locks for tailored Group 11 bis(amidine) complexes

“…S1, ESI†) are within the range of comparable CuCl complexes with coordination number two. 32 The resulting formation of two weak to moderately strong 33 N–H⋯Cl–Cu hydrogen bonds is evidenced by donor–acceptor distances of 3.34–3.36 Å (Table 1), which are similar in literature examples such as a CuCl complex with a tris(pyridyl-2-methyl)amine-based ligand (3.342(2) Å, 3.366(2) Å, and 3.418(2) Å) 4 b or the example shown in Fig. 2 (3.26 and 3.353 Å, no e.s.d.…”

Strongly Coupled Phenazine–Porphyrin Dyads: Light-Harvesting Molecular Assemblies with Broad Absorption Coverage

“…Phenazines are highly conjugated heterocycles that can be structurally modified by many convenient synthetic methods. − For example, a simple condensation of o -phenylenediamine derivatives with functionalized o -quinones directly permits a variety of polyaromatic-based structures. ,, Accordingly, they are widely used as building blocks for a wide range of applications, including anticancer agents, − fluorescent markers in biological systems, − electroactive materials for organic light-emitting diodes, , organic electronics, conductive polymers, photoredox catalysts, and as photoactive materials for photocatalysis and dye-sensitized solar cells (DSSCs). − Phenazines are particularly attractive as light-absorbing molecules because their absorption bands can be systematically tuned by increasing the number of arene rings (Figure ). However, the majority of reported phenazines have limitations from their low extinction coefficients and their maximum absorption occurring in the green visible region.…”