Color- and Morphology-Controlled Self-Assembly of New Electron-Donor-Substituted Aggregation-Induced Emission Compounds

• Published in: Langmuir Vol. 30; no. 9; pp. 2351 - 2359
• Main Authors: Niu, Caixia, Zhao, Liu, Fang, Tao, Deng, Xuebin, Ma, Hui, Zhang, Jiaxin, Na, Na, Han, Jingsa, Ouyang, Jin
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 11.03.2014
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la404436v

Four electron-donor-substituted aggregation-induced emission (AIE) compounds, N,N′-bis(4-methoxylsalicylidene)-p-phenylenediamine (BSPD-OMe), N,N′-bis(4-methylsalicylidene)-p-phenylenediamine (BSPD-Me), N,N′-bis(salicylidene)-p-phenylenediamine (BSPD), and N,N′-bis(4-hydroxylsalicylidene)-p-phenylenediamine (BSPD-OH), are designed and synthesized. They are all found to exhibit controlled self-assembly behaviors and good thermal properties. By changing the terminal electron-donor groups, they are controlled to self-assemble into three emission colors (green, yellow, and orange) and four morphologies (microblocks, microparticles, microrods, and nanowires) in THF/water mixtures. Their self-assembled structures were investigated with scanning electron microscopy (SEM), fluorescent microscopy images, transmission electron microscopy (TEM), and powder X-ray diffraction (PXRD) techniques. In addition, the emission colors of BSPD-OH can be successfully controlled to three colors (green → yellow → orange) through simply changing the water fraction (f w). Their thermal gravimetric analysis (TGA) results indicate that their thermal decomposition temperatures (T d, corresponding to 5% weight loss) range from 282 to 319 °C. Their differential scanning calorimetry (DSC) data show that BSPD-OH bears a glass-transition temperature (T g) of 118 °C. The good T d and T g values will ensure them to be luminogens for organic light-emitting diodes (OLEDs). The theoretical calculations and single-crystal X-ray diffraction (XRD) analysis of BSPD-OMe and BSPD suggest that the stronger electron donor substituent can twist the molecular conformation, decrease the degree of π conjugation, increase the energy gap, and then induce the emission colors’ blue shift and morphology variation. The results are meaningful in controlling the emission colors and self-assembly shapes of these derivatives, and they also provide a novel but facile way to get color-tunable AIE luminogens for OLEDs.