Protonation-State-Dependent Luminescence and Excited-State Electron-Transfer Reactions of 2- and 4-Pyridine (-ium)-Substituted Metallo-1,2-enedithiolates

Abstract

Luminescence and excited-state electron-transfer reactions of (dppe)Pt{S2C2(2-pyridine)(H)} and (dppe)Pt{S2C2(4-pyridine)(H)} (dppe = diphenyldiphosphinoethane) are enabled by protonation of the appended pyridine, thus serving as a novel means of electronic switching. The neutral complexes have low-lying d-to-d transitions that lead to rapid decay of excited states by nonradiative processes. However, upon protonation, a 1,2-enedithiolate-to-heterocycle π* intraligand charge-transfer transition (ILCT) becomes lower in energy than the d-to-d transition, thus giving rise to emissive 1ILCT* and 3ILCT* excited states for [(dppe)Pt{S2C2(2-pyridinium)(H)}][BF4] and [(dppe)Pt{S2C2(4-pyridinium)(H)}][BF4]. The assignment of these excited states was based on their energies and lifetimes (τ) which range from τ = 3 to 4 ns for the singlet and from τ = 2000 to 7500 ns for the triplet, respectively. Emission quantum yields (φ) increase with solvent polarity and range from φ = 0.0006 to 0.003 for the singlet and from φ ...