Synthesis and Properties of Covalently Linked Terpyridine‐BODIPY and Terpyridine‐3‐Pyrrolyl BODIPY Conjugates

A series of covalently linked terpyridine‐BODIPY and terpyridine‐3‐pyrrolyl BODIPY conjugates were synthesized by strategically tuning the position of the terpyridine moiety at the α and/or meso positions of the BODIPY (3–4) and 3‐pyrrolyl BODIPY cores (5–7). These compounds were synthesized over a sequence of synthetic steps and their identities were confirmed by HR‐MS, 1D, 2D NMR, and X‐ray crystallography of one of the conjugates and studied by various spectroscopic, electrochemical, and theoretical techniques. The presence of terpyridine moieties on BODIPY and 3‐pyrrolyl BODIPY cores significantly alters their electronic properties and these conjugates absorb strongly in the 505–640 nm region. Furthermore, the α‐terpyridinyl 3‐pyrrolyl BODIPY conjugate was used as a ligand to form heteroleptic ruthenium(II/III) complexes. The Ru(II)/Ru(III) complexes exhibit weak fluorescence with significantly reduced quantum yield and single‐state lifetime due to the presence of a heavy Ru(II)/Ru(III) ion, which enhances spin‐orbit coupling and increases the rate of intersystem crossing (ISC), leading to non‐radiative relaxation. DFT and TD‐DFT studies corroborated our experimental findings, providing deeper insights into the structural, photophysical, and electronic properties of these conjugates.