Synthesis, crystal structures, photophysical properties and self-assembly of fluorene-based bis-Schiff bases

Five fluorene-based derivatives (C1-C5) were conveniently synthesized and characterized. X-ray analysis revealed the molecular structures and column stacking in the single crystal of compound C1 and C4. Good thermal stability was observed by thermogravimetric analysis. Their optical properties were studied by UV-vis and fluorescence spectroscopy, and electrochemical properties were investigated by cyclic voltammetry (CV). Interestingly, SEM studies showed that C3 was assembled into 1D micron-scale ribbons with an average width of 1 μm and an average length exceeding 50 μm. STM imaging indicated that C1 can form ordered self-assembled monolayers on HOPG. Density functional theory method was employed to optimize the structure and analyze the electron distribution of compound C1-C3.