Synthesis of chiral TiO₂ nanofibre with electron transition-based optical activity.

Abstract

The optical chirality induced at the absorption bands due to electronic exciton coupling of the transition dipole moments between chromophores in close proximity is ubiquitous in helical organic materials. However, inorganic materials with optical activity resulting from electronic transitions have not been explored. Here we report the synthesis of chiral TiO(2) fibres via transcription of the helical structure of amino acid-derived amphiphile fibres through coordination bonding interactions between the organics and the TiO(2) source. Upon calcination, the as-prepared amorphous TiO(2) double-helical fibres with a pitch length of ~100 nm were converted to double-helical crystalline fibres with stacks of anatase nanocrystals in an epitaxial helical relationship. Both the amorphous and anatase crystalline helical TiO(2) fibres exhibited optical response to circularly polarized light at the absorption edge around ~350 nm. This was attributed to the semiconductor TiO(2)-based electronic transitions from the valence band to the conduction band under an asymmetric electric field.