The solid-state fluorescence of fluorophores is usually weakened or quenched by strong π-π interactions. Here, the solid-state fluorescence quantum yields (ΦSF) of tetrasubstituted tetrahydro-pyrimidines (TTHPs) are enhanced rather than decreased/or quenched by strong π-π interactions. All investigated TTHPs (5a−k) possess with aggregation-induced emission (AIE) characteristics: completely no emission in solutions owing to their soft, stero and low-conjugated molecular structures, but become emission upon aggregation, with ΦSF equal to 3%−87.7%, because of the formation of excellent through-bond/space/hyperconjugation-mixed electron cojugation system and radiative--transition-favored molecular packing modes as well as the restriction of molecular motions. Unexpectedly, achiral TTHPs aggregate via meso-enantiomers for 5k (both N1 and N3 atoms show pyramidal configuration) and via rac-enantiomers for other TTHPs (N1 shows racemic pyramidal inversion configurations and N3 shows planar configuration). Even more surprisingly, unlike conventional AIE fluorophores that can efficiently prevent cofacial π−π interaction, strong cofacial π−π interaction exists between the N1-inversion-based rac-enantiomers and can significantly enhance rather than decrease ΦSF values by efficiently decreasing knr values, which is first reported. Designing compounds with pyramidal inverstion might be an efficient stratgy to obtain highly emissive π−π stacking aggregates.

You have access to this article

Please wait while we load your content... Something went wrong. Try again?