Luminescence properties of metallo-supramolecular coordination polymers assembled from pyridine ring functionalized ditopic bis-terpyridines and Ru(ii) ion

Abstract

We present the study of photophysical properties of several Ru(II)-based metallo-supramolecular coordination polymers (MEPEs) constructed from various ditopic bis-terpyridines (bis-tpy) bearing electron-rich (OMe) or electron-deficient (Br) groups at the 6-position of the pyridyl periphery and having different spacers for connecting the two tpy moieties. The MEPEs are distinct from the frequently reported analogues derived from unsubstituted tpy. The photophysical properties such as emission spectroscopic properties and lifetime at both room temperature and 77 K are presented. The MEPEs are luminescent at room temperature with quantum yields (Φ_lum) < 10⁻⁶ and lifetimes on a timescale of nanoseconds (τ = ca. 6.6–22.4 ns), and display strong luminescence at 77 K with Φ_lum = ca. 0.21–2.5 × 10⁻² and lifetimes on a timescale of microseconds (τ = ca. 2.4–7.9 μs). More importantly, we find that introduction of either an electron-rich or an electron-deficient functional group at the 6-position of the ligands results in a clearly decreased absorption intensity of the derived MEPEs. This result is in contrast to the reported data in the literature where an increased intensity was observed when substitution occurred at the 4′-position of tpys, regardless of the electron-rich or electron-deficient nature of the substituents. In accordance with the absorption behaviour, substitution at the 6-position also leads to a notably different effect on the luminescent properties of the complexes. Thus, our results provide an alternative strategy for the de novo design of new materials.