Visible and Near-IR Emissions from k2 N- and k3 N-Terpyridine Rhenium(I) Assemblies Obtained by an [n×1] Head-to-Tail Bonding Strategy.

An [n×1] head-to-tail bonding strategy has been used for the synthesis of ReI metallacycles. From a k3 N-dicarbonyl precursor, a single discrete [4×1] square assembly was isolated and characterized, whereas a k2 N-tricarbonyl precursor led to two major species, a square and a [3×1] triangular assembly. Solid-state X-ray diffraction study has confirmed the high angular distortion (71° to 96°) of the k2 N precursors. The electrochemical reversibility of the triangular (5) and square (6, 7) assemblies is increased with respect to that of their precursors. Photophysical investigation has confirmed pronounced red-shifts in the emissions of the k3 N-dicarbonyl species 4 (935 nm) and 7 (980 nm), as confirmed by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations.