Rearrangement of the aggregation of the gelator during sol-gel transcription of a dimeric cholesterol-based viologen derivative into fibrous silica

New dimeric cholesterol-based viologen derivative 1 has been prepared and can form a very stable supergel in 1-butanol. To characterize the aggregation mode of 1 in the organogel phase, transmission electron microscopy (TEM) images, small-angle X-ray diffraction (SAXRD) patterns, and circular dichroism (CD) spectra were obtained. The TEM images show that 1 assembles into a fibrous structure composed of thin fibers with 10 nm diameters, which are derived from two twist unimolecular stacking fibers, and the dipole moments tend to orient in a clockwise direction as shown in the CD spectrum. The SAXRD pattern illustrates that the gelator maintains a layered structure with an interlayer distance of 4.96 nm. Therefore, we propose that a 1D helical column with a clockwise direction is the basic structural building block of the organogel fibers. On the other hand, the fibrous structure of the organogel is successfully transcribed into silica fibers with unique 15 nm inner diameters by the sol-gel polycondensation of tetraethoxysilane in the gel phase. It is first found that the aggregation of the gelator can rearrange into a stable hexagonal structure to lead to the hollow silica fibers with 15 nm inner diameters due to the adsorption of the oligomeric silica species onto the incipient cationic organogel fibers during the sol-gel transcription.