Photoinduced Chirality in Thin Films of Achiral Polymer Liquid Crystals Containing Azobenzene Chromophores

Abstract

Circular dichroism and circular birefringence were induced in thin films of achiral polymer liquid crystals containing 7 or 15 mol % azobenzene chromophores by irradiation with circularly polarized light (CPL). Circular dichroism was observed not only for the azobenzene moieties but also for the nonphotoactive mesogens, cyanobiphenyl groups, due to a cooperative motion. CPL with opposite handedness produces enantiomeric structures, and a chiroptical switch can be achieved by alternating irradiation with left and right CPL. The level of photoinduced chirality depends on the incorporation methods (doped or chemically bound) of the azobenzene chromophores, the amount of azobenzene units, and the sample temperature. The photoinduced circular dichroism can be erased by heating the films above the clearing temperatures or by annealing the films in the liquid-crystalline phase.

Synthesis and chiroptical properties of liquid crystalline copolymers containing azobenzene chromophores

“…The second negative Cotton effect located at about 359 and 430 nm with a crossover point at about 402 nm, and the negative CD band located at about 494 nm, are related to the n–π* electronic transition of azobenzene chromophores. The Cotton effects could be assigned to the presence of cooperative dipolar interactions between the neighboring azobenzene chromophores, as previously observed in several polymers bearing side‐chain azobenzene chromophores 24, 32, 33. The CD spectrum of copoly‐0.17 suggests that helical arrangements of the whole or at least some segments of the polymer occur in films of copoly‐0.17.…”

Stimuli-responsive conjugated polymers. Synthesis and chiroptical properties of polyacetylene carrying l-glutamic acid and azobenzene in the side chain

“…Jaycox and coworkers have found that azobenzene-modified polyaramides with atropisomeric 2,2 0 -binaphthyl linkages exhibit thermo-and photo-responsive chiroptical properties [5]. Rochon and coworkers have demonstrated the photo-induced chirality in thin films of achiral polymer liquid crystals containing azobenzene chromophores [6]. The photo-induced circular dichroism (CD) can be erased by heating the films above the clearing temperature of the polymer liquid crystals or by annealing the films.…”

Absolute asymmetric electrochemical polymerization

“…Control of both chirality of azobenzene liquid crystalline polymers with CPL and photo-induced chirality with CPL for amorphous azobenzene polymer films has been achieved [14][15][16][17][18]. Chirality induction for polyfluorene derivatives having no photochromic groups in thin film form upon irradiation of CPL was reported [19].…”