Chirality amplification of syndiotactic polystyrene induced circular dichroism chiral film in δ form upon annealing

Chiroptical Properties in Thin Films of π-Conjugated Systems

Chiral π-conjugated molecules provide new materials with outstanding features for current and perspective applications, especially in the field of optoelectronic devices. In thin films, processes such as charge conduction, light absorption, and emission are governed not only by the structure of the individual molecules but also by their supramolecular structures and intermolecular interactions to a large extent. Electronic circular dichroism, ECD, and its emission counterpart, circularly polarized luminescence, CPL, provide tools for studying aggregated states and the key properties to be sought for designing innovative devices. In this review, we shall present a comprehensive coverage of chiroptical properties measured on thin films of organic π-conjugated molecules. In the first part, we shall discuss some general concepts of ECD, CPL, and other chiroptical spectroscopies, with a focus on their applications to thin film samples. In the following, we will overview the existing literature on chiral π-conjugated systems whose thin films have been characterized by ECD and/or CPL, as well other chiroptical spectroscopies. Special emphasis will be put on systems with large dissymmetry factors (g_abs and g_lum) and on the application of ECD and CPL to derive structural information on aggregated states.

Supramolecular chirality of amphiphilic block copolymer films made through two steps: self-assembling first, and then solution coating

Supramolecular chirality is achieved in amphiphilic block copolymer films made through two-step fabrication: self-assembling first and then solution coating. The amphiphilic block copolymer is composed of poly(N-isopropyl acrylamide) (pNIPAM) as hydrophilic segments and poly(methyl methacrylate) with chiral side groups as hydrophobic segments. The films fabricated by two steps show sensible circular dichroism (CD) signals around a wavelength of 200 nm. However, CD signals cannot be detected from films made by directly coating the solution of copolymers on the quartz surface. The CD signal at about 200 nm is from supramolecular arrangement of benzene units connected to the chiral group in the hydrophobic segment. This result is thought to be originated from the aggregation of the copolymer during the first step of the film forming process, and the corresponding investigation into factors affecting this process has been performed in this work. It is also found that the films fabricated by two steps can adsorb chiral small molecules enantioselectively, while the films obtained by coating the solution of copolymers directly have no such enatioselective adsorption ability.

Chirality on Amorphous High-Tg Polymeric Nanofilms: Optical Activity Amplification by Thermal Annealing

The chiroptical properties of amorphous chiral polymers functionalized with conjugated trans-azoaromatic chromophore linked to the backbone through a chiral cyclic pyrrolidine moiety of one single configuration at the solid state, as thin films, were investigated. For the first time nanometric thin films of amorphous polymers (not liquid crystals) showed a remarkable chiral amplification upon thermal treatment at a temperature close to their Tg. The side-chain azobenzene chromophores rearrangement driven by the enhanced chain mobility seems to favor the formation of nanodomains of conformationally ordered macromolecular chains with one prevailing helical handedness whose optical activity depends on the configuration of the intrinsic chirality of the monomeric units and which as a result are stable at room temperature for a long time.

Enantiomeric guests with the same signs of chiral optical responses

The chiral response of non-racemic molecules, being guests of s-PS co-crystalline films, does not depend on their R or S molecular chirality but essentially only on the polymer host supramolecular chirality.