Crystal Structures and Fluorescence Spectroscopic Properties of a Series of α,ω‐Di(4‐pyridyl)polyenes: Effect of Aggregation‐Induced Emission

Abstract

Crystal structures and fluorescence spectroscopic properties were investigated for a series of all-(E) α,ω-di(4-pyridyl)polyenes (1-5) with different number of double bonds (n). Molecules 1 and 2 (n = 1, 2) in crystals are arranged to form partially πoverlapped structures, whereas those of 3-5 (n = 3-5) are stacked in a herringbone fashion. All these molecules, the shorter polyenes in particular, are almost nonfluorescent in solution. In the solid state, 1 and 2 are highly emissive as pure organic solids [fluorescence quantum yields (ϕ f) = 0.3-0.5], while 3 and 4 are only weakly fluorescent (ϕ f < 0.05). The strongly n-dependent fluorescence properties can be attributed to the largely different molecular arrangements in the crystals. Although 5 is nonfluorescent in the solid state, we observe a very clear structure-property relationship in 1-4. Compounds 1 and 2 become much more emissive in the solid state than in solution as a result of the aggregation-induced emission (AIE) effect.

Design of Fmoc-Phenylalanine Nanofibrillar Hydrogel and Mechanistic Studies of Its Antimicrobial Action against Both Gram-Positive and Gram-Negative Bacteria

“…The resultant pH of the G2 (TSC) hydrogel helped to attain the zwitterionic state, which decreased the electrostatic repulsion between monomers, resulting in closer association of monomer units, leading to fluorescence. The crystalline arrangement of G2 may also contribute to its fluorescence property . Further, the fluorescence of hydrogels was confirmed through fluorescence microscopic imaging of self-assemblies (Figure b).…”

“…The crystalline arrangement of G2 may also contribute to its fluorescence property. 37 Further, the fluorescence of hydrogels was confirmed through fluorescence microscopic imaging of self-assemblies (Figure 6b). Both data support the fluorescence property of G2 (TSC) (Figure 6a,b).…”