Homochiral Supramolecular Thin Film from Self-Assembly of Achiral Triarylamine Molecules by Circularly Polarized Light

Abstract

Here, we report the formation of homochiral supramolecular thin film from achiral molecules, by using circularly polarized light (CPL) only as a chiral source, on the condition that irradiation of CPL does not induce a photochemical change of the achiral molecules. Thin films of self-assembled structures consisting of chiral supramolecular fibrils was obtained from the triarylamine derivatives through evaporation of the self-assembled triarylamine solution. The homochiral supramolecular helices with the desired handedness was achieved by irradiation of circularly polarized visible light during the self-assembly process, and the chiral stability of supramolecular self-assembled product was achieved by photopolymerization of the diacetylene moieties at side chains of the building blocks, with irradiation of circularly polarized ultraviolet light. This work provides a novel methodology for the generation of homochiral supramolecular thin film from the corresponding achiral molecules.

Chiroptical Properties in Thin Films of π-Conjugated Systems

“…Interestingly, the authors simulated the ECD spectrum of isolated π-conjugated systems in a twisted conformation by using the DeVoe coupled oscillator calculation approach. A similar CP-light-induced chirality was also found in thin films of achiral hydrogen-bonded complexes of azobenzene and melamine derivatives, triarylamine-based achiral compounds, as well as in samples of organogels based on an achiral small molecule azobenzene gelator . This latter is thought to acquire a twisted conformation in the gel form consistent with the one observed in the crystal, as confirmed by TD-DFT calculations of ECD spectra.…”

Spontaneous Deracemizations

“…These are given by reported enantioselective behavior on ferromagnetic surfaces due to spin-polarization , as well as the vortex-induced chiral sign induction in open flow systems . Along with these observations, reaction systems giving rise to asymmetric amplification processes have been shown to enhance the usually small ee values obtained through physical forces as for instance, during the CPL irradiation of the Soai reaction, as well as during the Viedma deracemization or the self-assembly of nanostructures. − Hence it became evident that from the coupling between chiral physical forces and appropriate amplification processes, such as enantiospecific autocatalysis, high ee values can be achieved, which could play a prominent role for possible scenarios in the abiotic origin of biomolecular homochirality. On the other hand, parity violation, as one prominent and frequently debated candidate for directed asymmetry induction in respect to such scenarios, has to be taken as with skepticism at the current state …”

“…The chirality induction and modulation of polymers by CPL has been reviewed recently . In further regards to self-assembled structures, lately homochiral supramolecular structures were obtained from achiral triarylamine derivatives, achiral porphyrin derivatives through irradiation with CPL (Figure ), as well as the irradiation of gold salt solutions that result in the formation of gold nanoparticles and their assembly into chiral nanostructures . Furthermore, significant chiral biases of around ee = 25% were observed in the static crystallization of sodium chlorate when the nucleation was induced by the optical trapping of Ag nanoparticles during irradiation with right- or left-handed laser CPL …”

Circularly Polarized Light‐Driven Supramolecular Chirality

“…Li et al also reported the emergence of supramolecular chirality by CPL with a stilbene-extended TPA core. [84] While they interestingly demonstrated the induction, modulation, and locking of the supramolecular chirality by CPL, a plausible mechanism explaining the light-matter chirality transfer was not provided.…”