Aggregation-Induced Emission from Titanium Complexes Supported by Imido and Phosphinic Amidato Ligands

Treatment of Ti(NMe₂)₄ with diphenylphosphinic amides Ph₂P(O)(NHR) (R = Me, Ph) followed by reaction with tert-butylamine afforded dimeric complexes {Ti(N^tBu)[κ²-Ph₂P(O)(NR)][μ₂-Ph₂P(O)(NR)]}₂ (R = Ph, 3; Me, 4), which were characterized crystallographically. Variable-temperature NMR studies demonstrated significant structural flexibility of both compounds in solution, and Eyring analysis suggests intramolecular conformational fluxionality of the eight-membered Ti₂N₂P₂O₂ metallacycles. While nonemissive in THF solution at room temperature, both complexes exhibit aggregation-induced emission upon the addition of hexane as a counter solvent. Solid-state photoluminescence bands occur with maxima at 648 and 632 nm for 3 and 4, respectively, with quantum yields of 4.3% and 6.3% and long-lived emission lifetimes (6.8 and 3.4 μs, respectively). Time-dependent density functional theory calculations reveal that the low-energy absorption features originate from mixed π_(Ti=N) to π_(P-phenyl) and π_(Ti=N) to d_(Ti) charge transfer transitions.