π‑Conjugated Polymer Anisotropic Organogel Nanofibrous Assemblies for Thermoresponsive Photonic Switches

The
present work demonstrates one of the first examples of π-conjugated
photonic switches (or photonic wave plates) based on the tailor-made
π-conjugated polymer anisotropic organogel. New semicrystalline
segmented π-conjugated polymers are designed with rigid aromatic
oligophenylenevinylene π-core and flexible alkyl chain along
the polymer backbone. These polymers are found to be self-assembled
as semicrystalline or amorphous with respect to the number of carbon
atoms in the alkyl units. These semicrystalline polymers produce organogels
having nanofibrous morphology of 20 nm thickness with length up to
5 μm. The polymer organogel is aligned in a narrow glass capillary,
and this anisotropic gel device is further demonstrated as photonic
switches. The glass capillary device behaves as typical λ/4
photonic wave plates upon the illumination of the plane polarized
light. The λ/4 photonic switching ability is found to be maximum
at θ = 45° angle under the cross polarizers. The orthogonal
arrangements of the gel capillaries produce dark and bright spots
as on-and-off optical switches. Thermoreversibility of the polymer
organogel (also its xerogel) was exploited to construct thermoresponsive
photonic switches for the temperature window starting from 25 to 160
°C.
The organic photonic switch concept can be adapted to large number
of other π-conjugated materials for optical communication and
storage.