67232-08-0

Upstream product

• 646-24-2 1.9-diaminononane 
• 90-02-8 salicylaldehyde 

Relevant academic research and scientific papers

Functionalized Salen ligands linking with non-conjugated bridges: unique and colorful aggregation-induced emission, mechanism, and applications

A series of novel, simple, and colorful Salen ligands (56 samples), salicylaldehyde-based bis-Schiff bases, linking with different non-conjugated alkyl bridges ((CH2)n, n = 2-9, 12; cyclohexyl) and containing different electron-accepting (-NO2, -F, and -Cl), electron-donating (-OMe, -OH, and -NEt2), or sterically hindering (-t-butyl) substituents or a π-extended system (naphthalene ring) have been designed and synthesized. The photophysical properties of these Salen ligands can be well-tuned by the introduction of side functional substituents, π-extended systems, and central N-alkyl chain bridges. It is unusual that they contain a small π-conjugated system but display strong blue, green, and red aggregation-induced emission (AIE) with large Stokes shifts (up to 162 nm) and high fluorescence quantum yields (up to 0.44 and 0.75 in water and in solid, respectively). Combining with their advantages of AIE and good stability and biocompatibility, the Salen ligands can be potentially used in mechanofluorochromism (crystal-defect-induced emission) and living cell imaging. Moreover, the inherent relationships between their chemical structures and AIE properties are studied, which provide unequivocal insights for the design of AIE-active dyes.

Effects of diamine bridge length and substituents on the spectral properties of N,N′-bis(α-substituted salicylidene)diamines in solution

Absorption and fluorescence spectra of thirteen N,N′-bis(α-substituted salicylidene)diamines in solution were investigated with the intention of investigating the role of the substituent and diamine bridge length on their optical properties. The fluorescence efficiency was improved by an increase in the electron-donating property of the substituents on the azomethine carbon accompanied by an increase of the n→π* transition absorption. However, the effect did not occur for the substituents on the azomethine nitrogen, in which no drastic changes in fluorescence efficiency could be observed. Through the investigation of the diamine bridge length effects, it was found that a diamine Schiff base seems to form neither an inter- nor an intramolecular dimer with any peculiar fluorescence in the solution even if it has a long methylene bridge. It was also suggested that the diamine Schiff base has a third fluorescence species in the excited state, which might be a pre-keto form, the existence of which is strongly affected by the hydrogen bond strength between the hydroxy and azomethine groups.