Schiff base particles with aggregation-induced enhanced emission: random aggregation preventing π–π stacking

Abstract

Three Schiff bases containing phenylbenzoxazole were synthesized and characterized, which exhibited distinct aggregation-induced enhanced emission (AIEE) behavior in THF-water. However, the singlecrystals of L3 show obvious p-p stacking that would induce fluorescent quenching in the solid state. In order to further gain insight into the AIEE mechanism of the three compounds, the size and growth process of particles with different water fractions were studied using SEM, TEM and DLS. The results show that the molecules of compounds can slowly assemble in an ordered fashion to form morecrystalline but less-emissive particles in the THF-water mixtures with low water contents, while in mixtures containing very large amounts of water, the molecules of compounds abruptly agglomerate to form less-crystalline or even amorphous but more-emissive clusters, which effectively avoid p-p stacking. Fig. 1 Molecular structures of L1-L3.

Hydrogen‐Bond and Supramolecular‐Contact Mediated Fluorescence Enhancement of Electrochromic Azomethines

“…The emission enhancement modes have principally been from aromatic stacking [13] or weak bindingo fa na nalyte. These have relied on the imine nitrogen to promote intermolecular =N···HSÀ [16] and =N···HCÀ [17] bonds in addition to intramolecular =N···HOÀ [17] supramolecular contacts. These have relied on the imine nitrogen to promote intermolecular =N···HSÀ [16] and =N···HCÀ [17] bonds in addition to intramolecular =N···HOÀ [17] supramolecular contacts.…”

“…Although it was recently demonstrated that supramolecular contacts that drive crystallization in the solid state can be used for AIE enhancement, only a limited number of examples have used such contacts for enhancing the fluorescence of azomethines. These have relied on the imine nitrogen to promote intermolecular =N⋅⋅⋅HS− and =N⋅⋅⋅HC− bonds in addition to intramolecular =N⋅⋅⋅HO− supramolecular contacts.…”

Conjugates of Benzoxazole and GFP Chromophore with Aggregation‐Induced Enhanced Emission: Influence of the Chain Length on the Formation of Particles and on the Dye Uptake by Living Cells

“…On the one hand, the 2‐phenylbenzoxazole fragment bore its chemical and photochemical stability together with excellent optical properties that make it the basis of widely used fluorescent materials . It must be underlined that this motif leads to many derivatives that are strongly emissive in the solid state and sometimes display AIE behavior . On the other hand, many synthetic derivatives of the GFP chromophore display fluorescence enhancement upon rigidification, for example after inclusion in a protein matrix, hence their use for biological imaging .…”

Novel highly emissive H-aggregates with aggregate fluorescence change in a phenylbenzoxazole-based system

“…The targeted molecules show strong absorption bands at 388, 327 and 414 nm, respectively, and emission maxima (λ em ) at 499, 389 and 495nm, respectively. The weak absorption peaks at 300-320 nm that are 45 mainly attributed to π-π* electronic transitions derived from the benzoxazolyl-benzene unit 9 . The molar extinction coefficient values also are in agreement with π-π* transitions 10 .…”