Morphological Evolution of Strongly Fluorescent Water Soluble AIEEgen-Triblock Copolymer Mixed Aggregates with Shape-Dependent Cell Permeability

Fine-Tuning the Excited-State Dynamics of Heteroleptic Ruthenium(II) Polypyridyl Complexes with Systematic Variation of Benzazole-Substituted 8-Hydroxyquinolines

A series of structurally related bistridentate heteroleptic Ru(II) polypyridyl complexes, [RuII(ttpy)(8-HQLS/N/O)]+ (Ru1-Ru3), were synthesized, where ttpy = p-tolyl terpyridine and 8-HQLS/N/O are monoanionic N^N^O-donor tridentate ligands (8-HQLX), derived from 8-hydroxyquinoline (8-HQ), namely, 8-HQLS = 2-(2'-benzothiazole)-8-hydroxyquinoline, 8-HQLN = 2-(2'-benzimidazole)-8-hydroxyquinoline, and 8-HQLO = 2-(2'-benzoxazole)-8-hydroxyquinoline. The electronic structures of these rigid ligands were systematically tuned by varying the noncoordinating heteroatoms (S, O, NH) in the five-membered heterocyclic ring, impacting the electronic properties, redox potentials, excited-state lifetime/dynamics, and deactivation pathways and photophysical behavior of the corresponding Ru(II) complexes. Notably, [RuII(ttpy)(8HQLN)]+ (Ru2) exhibited an excited-state lifetime (τ > 1 ns in CH3CN at RT) surpassing that of the homoleptic complex [Ru(ttpy)2]2+ (τ ∼ 0.62 ns), despite its more distorted octahedral geometry. These heteroleptic complexes (Ru1-Ru3) showed extended excited-state lifetimes compared to their homoleptic counterpart Ru4. The complexes displayed absorption in the red region, which is favorable for phototherapeutic applications. Their relative singlet oxygen (1O2) quantum yields (ΦΔ) in CH3CN ranged from 0.03 to 0.10. Given their reasonable excited-state lifetimes and 1O2 generation ability, these Ru(II) complexes demonstrated potential as photocatalysts for organic substrates, as evidenced by their effectiveness in the photooxidation of PPh3 to Ph3P=O as a model reaction.