Hydrogen Bonding‐Induced Inversion and Amplification of Circularly Polarized Luminescence (CPL) in Supramolecular Assemblies of Axially Chiral Luminogens
Sandipan Ghorai, Soumyadip Show, Anindita Das
Abstract
Abstract Herein, we report the self‐assembly and chiroptical properties of two axially chiral π‐conjugated luminogens, R‐ NMI and S‐ NMI , each equipped with two pyridyl moieties for hydrogen (H)‐bonding with chiral diacids. The two enantiomers display aggregation‐induced emission enhancement (AIEE) and increased CD and CPL signals in the self‐assembled state with a high g lum value of 1.5 (±0.06)×10 −2 in 1:9 dioxane:methylcyclohexane. Crystallographic analysis confirmed mirror‐image helical structures for R ‐NMI and S ‐NMI involving both intra‐ and intermolecular π‐π stacking, leading to elongated hexagonal platelets. Supramolecular co‐assembly of R‐ NMI with D ‐ and L ‐tartaric acids ( D ‐TA and L ‐TA ) could remarkably modulate and invert the chiroptical properties of R‐ NMI , which is unachievable with control chiral monoacids. The co‐assembled structures were driven by pyridine‐carboxylic acid H‐bonding as revealed from the crystal structure analysis, which was also supported by computational studies. Strikingly, R ‐NMI+ D ‐TA leads to an exceptionally high fourfold amplification in the g lum value [5.4 (±0.04)×10 −2 ] with an inverted sign, which additionally demonstrates intriguing temperature‐dependent switching. In contrast, R ‐NMI+ L ‐TA results in a threefold reduction in the g lum value [0.54 (±0.015)×10 −3 ], also with an inverted sign compared to R ‐NMI alone, establishing a clear strategy for chiral discrimination between the two enantiomers of TA .