Unusual Aggregation/Gelation-Induced Phosphorescence of Propeller-Type Binuclear Platinum(II) Enantiomers

Three binuclear cyclometalated Pt-II complexes, [(ppy)Pt(mu-SA)Pt(ppy)] (ppy = 2-phenylpyridine, SA: salicylaldehyde azine), have been synthesized and characterized. Owing to the blockage of the intramolecular rotation of the bridging SA ligands, all three complexes exhibit propeller-type enantiomers and aggregation-induced phosphorescence (AIP). Interestingly, one complex with -NEt2 groups instead of long alkyl chains, amide, urea peptides, cholesterol, sugar, or steroidal groups was found to show strong phosphorescence enhancement gated by the gelation process. This unusual gelation behavior is rarely encountered, as the metallogel has no intermolecular hydrogen bonding or Pt-Pt interactions. We attribute the driving force of this gelation-induced phosphorescence (GIP) to the propeller-type structure, optimally balanced solubility of -NEt2 groups, enantiomer-induced - stacking interactions, and strong multiple intermolecular H-C, H-O, and H-H interactions.