Photoinduced Tuning of Optical Stop Bands in Azopolymer Based Inverse Opal Photonic Crystals

Abstract

Photo‐tunable photonic crystals were prepared from three dimensional (3D) colloidal crystal templates using a photoresponsive azopolymer. For the preparation of azopolymer infiltrated photonic crystals, silica colloidal crystals were fabricated by gravity sedimentation, a self‐assembly technique. The interstitial voids between colloidal particles were filled with azopolymer and azopolymer inverse opals were produced by treatment with aqueous hydrofluoric acid. These photonic crystals exhibited stop bands in their transmission spectra measured in the normal incidence to the (111) plane of face centered cubic (fcc). The photonic bandgap of the azopolymer infiltrated opal and inverse opal could be controlled by the refractive index change due to the photoinduced orientation of azobenzene chromophores. When the azopolymer photonic crystals were irradiated with linearly polarized light, their bandgap positions were shifted to shorter wavelength regions with increasing irradiation time. This behavior experimentally produced a photoinduced orientation of the azobenzene groups in parallel with the incidence of the excitation light. Through such an out‐of‐plane orientation of azo chromophores, parallel to the [111] fcc crystallographic axis, the effective refractive index of the photonic crystal medium was decreased. Therefore, a blue‐shift in bandgap positions was consequently induced with 20–40 nm tuning ranges. The out‐of‐plane orientation was confirmed by angular resolved absorption spectral measurements.

Tunable Colors in Opals and Inverse Opal Photonic Crystals

“…[ 36 ] They showed the ability to blue shift the stop band when the azo-polymer was excited by an Ar + laser at 488 nm. Azobenzene groups in the polymer were oriented by the linearly polarized irradiation, and this alignment reduced the effective refractive index of the polymer.…”

Optical and Physical Applications of Photocontrollable Materials: Azobenzene-Containing and Liquid Crystalline Polymers

“…As a result, the refractive index change increased under irradiation, and a shift in the spectral maximum of more than 55 nm was achieved. The inverse opal structure can be also fabricated from a photocontrollable polymer as reported by Kim and coworkers [42]. Silica colloidal crystals were infiltrated with a solution of azopolymer (poly(disperse orange 3)), and the solvent was evaporated.…”

Facile fabrication of mechanochromic-responsive colloidal crystal films

“…Yin and co-workers prepared colloidal crystal with magnetically tunable stop band covering the entire visible spectrum [6,7]. Colloidal crystal with tunable photonic band gap can also be achieved through the application of electric-field, [8,9] pH [10], temperature [11], UV-irradiation [12,13] and solvent [14][15][16].…”