Raman Optical Activity Enhanced via Supramolecular Aggregation and Other Intermolecular Interactions-A Review

In this review, we show that Raman optical activity (ROA) combined with electronic circular dichroism (ECD) are effective tools for detecting supramolecular chirality and related processes such as chiral signal amplification and chirality transfer (also called induction) between chiral and achiral solutes. Research on spontaneous self-organization has led to significant discoveries in vibrational optical activity (VOA) over the past decade. As a leading topic, we discuss different aggregation pathways of carotenoids, which contributed to the definition of new phenomena in the field of ROA, i.e., aggregation-induced resonance Raman optical activity (AIRROA), and the first chirality induction observed in nature. We present the chirality of carotenoids as i) amplification via supramolecular assembly, ii) induction by a small number of chiral monomers, and iii) transfer from the local environment. We also report here other complex systems that are relevant to the VOA community in the context of chiroptical analysis. These include ROA signal enhancement, e.g., recorded for amyloid fibrils or achiral linker aggregates attached to silver colloid (plasmonic effects). Finally, we highlight the challenges faced by ROA studies of supramolecular aggregates of strongly absorbing compounds, where chirality transfer may be misinterpreted as artifacts due to the ECD-Raman effect.