1,2,5,6‐Tetrakisguanidino‐naphthalenes: Electron Donors, Fluorescent Probes, and Redox‐Active Ligands

In this work we report new redox-active 1,2,5,6-tetrakis(guanidino)-naphthalene compounds, isolable and storable in the neutral and deep-green dicationic redox states, and oxidizable further in two one-electron steps to the tetracations. Protonation switches on blue fluorescence, with the fluorescence intensity (quantum yield) increasing with the degree of protonation. Reactions with N -halogeno-succinimides or N -halogeno-phthalimides lead to a series of new redox-active halogeno- and succinimido-/phthalimido-substituted derivatives. We propose these highly selective reactions to proceed via the tri- or tetracationic state as intermediate. The derivatives are oxidized reversibly at slightly higher potentials than the unsubstituted compounds to dications and further to tri- and tetracations. Finally we show that the integration as redox-active ligands in transition-metal complexes shifts the redox-potentials to higher values and also allows reversible oxidation in two potentially-separated one-electron steps.