Fluorescent organogels as templates for sol–gel transcription toward creation of optical nanofibers

Abstract

1,10-Phenanthroline-appended cholesterol-based gelators (1 and 2) and their non-gelling reference compounds (1′ and 2′) were synthesized. It was shown that the gelation abilities of 1 and 2 are quite different, in spite of their structural similarity. Compound 1 can form gels with various kinds of organic solvents, whereas 2 is capable of gelation only in acidic solvents. This difference in gelation abilities seems to be due to the difference in the stacking mode of the phenanthroline moieties, as confirmed by CD spectra. TEM and AFM observations showed that fibrillar aggregates are entangled in a three-dimensional network structure. The gels also showed beautiful fluorescence, characteristic of their molecular structures and gelation conditions (in the presence and the absence of acid). Organic assemblies thus characterized were subjected as templates for sol–gel polycondensation of metal alkoxide such as tetraethyl orthosilicate (TEOS) and tetra-n-butyl titanate. The resultant organic–inorganic composite materials showed the same fluorescence properties as the organic gels. After calcination, it was revealed by TEM observation that the silica and titania materials have a hollow structure, indicating that the sol–gel polycondensation reaction proceeds selectively at the surface of the organic assemblies. The CD spectrum of the organic–inorganic composite was similar to that of the organogel, indicating that the aggregation stacking mode of the original phenanthroline moieties is still retained even in the silica-gel phase. The organic–inorganic hybrids obtained are expected to lead to various nanostructured optoelectronic devices.