This tutorial provides a comprehensive description of the origin of chiroptical properties of supramolecular and plasmonic assemblies in the UV–visible region of the electromagnetic spectrum.

The chemical and physical properties of molecules and materials are known to be modified significantly under vibrational strong coupling (VSC). In order to gain insight into the effects of VSC on − interactions involved in molecular self-assembly, themselves sensitive to vacuum electromagnetic field fluctuations, the aggregation of two structural isomers (linear and V-shaped) of phenyleneethynylene under cooperative coupling was investigated. By coupling the aromatic C=C stretching band, the assembly of one of the molecules results in the formation of spheres as opposed to flakes under normal conditions. As a consequence, the electronic absorption and emission spectra of the self-assembled structures are also modified significantly. The VSC induced changes depend not only on the type of vibration that is coupled but also on the symmetry of the phenyleneethynylene isomer. These results confirm that VSC can be used to drive molecular assemblies to new structural minima and thereby provide a new tool for supramolecular chemistry.

Silicon-based light-emitting materials have emerged as a favorable substitute to various organic and inorganic systems due to silicon’s high natural abundance, low toxicity, and excellent biocompatibility. However, efforts on the design of free-standing silicon nanoparticles with chiral non-racemic absorption and emission attributes are rather scare. Herein, we unravel the structural requirements for ligand-induced chirality in silicon-based nanomaterials by functionalizing with D- and L-isomers of a bifunctional ligand, namely, tryptophan. The structural aspects of these systems are established using high-resolution high-angle annular dark-field imaging in the scanning transmission electron microscopy mode, solid-state nuclear magnetic resonance, Fourier transform infrared, and X-ray photoelectron spectroscopy. Silicon nanoparticles capped with L- and D-isomers of tryptophan displayed positive and negative monosignated circular dichroic signals and circularly polarized luminescence indicating their ground- and excited-state chirality. Various studies supported by density functional theory calculations signify that the functionalization of indole ring nitrogen on the silicon surface plays a decisive role in modifying the chiroptical characteristics by generating emissive charge-transfer states. The chiroptical responses originate from the multipoint interactions of tryptophan with the nanoparticle surface through the indole nitrogen and −CO2 – groups that can transmit an enantiomeric structural imprint on the silicon surface. However, chiroptical properties are not observed in phenylalanine- and alanine-capped silicon nanoparticles, which are devoid of Si–N bonds and chiral footprints. Thus, the ground- and excited-state chiroptics in tryptophan-capped silicon nanoparticles originates from the collective effect of ligand-bound emissive charge-transfer states and chiral footprints. Being the first report on the circularly polarized luminescence in silicon nanoparticles, this work will open newer possibilities in the field of chirality.

The phenomenon of excited-state symmetry breaking is often observed in multibranched molecular systems, significantly affecting their photophysical and charge separation behavior. As a result of this phenomenon, the electronic...