Thirty years of ionic liquids: a personal perspective

Over the past 30 years, ionic liquids (ILs) have emerged as a versatile class of compounds, bridging fundamental research and applied chemistry. This work offers a historical perspective on ILs, mainly covering fundamental and structural aspects, filtered through the author's personal experience and with no claim of completeness, focusing on four milestone topics: nanostructuring at the mesoscopic level, nanostructuring at the atomic level via intermolecular nuclear Overhauser effect (NOE) studies, the unexpected ability of ILs to selectively dissolve gases, and their potential in promoting sustainable chemistry. These aspects have expanded our understanding of ILs beyond their initial classification as merely molten salts. Among the many challenges ILs face, sustainability is a key factor shaping their present and future applications. As environmental policies evolve, IL-based processes must be evaluated through life cycle assessment and green metrics. However, sustainability extends beyond toxicity and biodegradability, requiring a broader assessment of ecosystem impact and societal acceptance. Addressing these challenges demands a multidisciplinary approach, integrating chemistry with environmental science and engineering. By embracing these perspectives, ILs can continue to drive greener and more efficient chemical processes in the 21st century.