Antenna-Enhanced Triplet-State Emission of Individual Mononuclear Ruthenium(II)-Bis-terpyridine Complexes Reveals Their Heterogeneous Photophysical Properties in the Solid State

The ability of supramolecular transition metal coordination complexes to form stabilized, long-living, radiative charge-separated states has drawn interest to employ these triplet-state emitters for the design of photonic devices. Their applicability as photosensitizers of electron transfer in molecular photonic systems is directly coupled to fundamental studies of their rich and highly versatile photochemical and photophysical properties. Here, we demonstrate that the properties of individual dual-luminescent Ru²⁺-bis-terpyridine complexes can be addressed with excellent sensitivity in single-complex antenna-enhanced phosphorescence investigations. This sensitivity enables studying environmentally imposed alterations of their photophysical properties, e.g., in thin film applications. In contrast to ensemble averaging investigations in solution, single-complex antenna-enhanced phosphorescence investigations corroborate the existence of Ru²⁺-bis-terpyridine complexes with spectrally shifted emission peaks and diverging intrinsic quantum yields in the solid state. Across the sample of investigated individual complexes the observed emission spectra resemble the expected unique features of this specific Ru²⁺-bis-terpyridine complex. The origin of the shifted emission is discussed in terms of the existence of different molecular conformers of this specific Ru²⁺-bis-terpyridine complex facilitated by the embedment into a rigid solid matrix.