Molecular-Oriented Self-Assembly of Small Organic Molecules into Uniform Microspheres

Self-assembly of small organic π-conjugated molecules into micro- and nanostructures has drawn much attention because of their wide applications in miniature optoelectronic devices. Many efforts have been focused on the controlled fabrication of organic micro/nanostructures, which are determined by various factors including kinetic and thermodynamic process but still remain poorly understood. In our research, two π-conjugated molecules of (E)-3-(4-(diphenylamino)­phenyl)-1-(4-fluoro-2-hydroxyphenyl)­prop-2-en-1-one (DFHP) and (E)-3-(4-(bis­(4-methoxyphenyl)­amino)­phenyl)-1-(4-fluoro-2-hydroxyphenyl)­prop-2-en-1-one (DFPHP) with a small difference of substituent groups were designed and synthesized. By the solution-exchange method, DFHP are self-assembled into amorphous microspheres while DFPHP tend to grow into crystalline rhombic microcrystals. The head of DFHP organic molecules can form hydrogen bonds with ethanol molecules and the tail of DFHP dissolves in the dichloromethane (DCM) phase, which exhibits amphiphilic nature, contributing to the self-assembly of microspheres. In a contrast, both the head and the tail of DFPHP can have hydrogen bonds with the ethanol molecules, which leads to the ordered DFPHP molecular packing and then the formation of rhombic microcrystals. Furthermore, based on simulated growth/equilibrium morphology, DFHP form the amorphous microspheres other than the crystalline microcrystals due to the lower attachment energy (E_total = −43.5 kcal/mol) as compared with that (E_total = −53.1 kcal/mol) of DFPHP. Our demonstration can indeed builds the structure–morphology relationship for rational fabrication of organic micro/nanostructures, which would contribute to integrated optoelectronics.