Action-based two-dimensional infrared spectroscopy on the horizon

Time domain two-dimensional infrared (2DIR) spectroscopy extends the capabilities of traditional infrared spectroscopy by revealing information on vibrational modes' anharmonicities, couplings, and energy transfer processes, making it a powerful tool for studying fast dynamic processes. Recent advancements in mid-IR laser technology and detection methods have significantly improved the resolution and acquisition rate of 2DIR spectroscopy. Despite these exciting developments, 2DIR spectroscopy remains limited by Abbe's diffraction limit, which restricts its spatial resolution. Aimed to address this challenge, the integration of action-based detection methods, notably the atomic force microscope (AFM)-based photothermal detection, offers a promising solution. AFM-2DIR spectroscopy combines the high spatial resolution of AFM with the richness of molecular insights of 2DIR, allowing nanoscale analysis of heterogeneous samples. This new type of technique would open avenues for investigating complex molecular systems, surface phenomena, and nanostructures with unprecedented spatial precision, offering potential for research in chemistry, materials science, bio-macromolecules, and nanotechnology for the chemical physics community.