In Situ Optical Imaging-Enabled New Insights into Nanoscale Photofunctional Materials: Visualization, Manipulation, and Beyond.

Photofunctional materials, especially semiconductors and plasmonic metals, have attracted increasing interest for solar energy harvesting and utilization. Structurally engineering these materials into the nanoscale remarkably enhances their efficiencies. However, this also exacerbates the structural complexities and heterogeneous activities among individuals and compromises the efficiencies of traditional bulk-level activity measurements. Over the last decades, in situ optical imaging has emerged as a promising tool to disentangle such heterogeneities of activities among individuals. Through the discussion of representative work in this Perspective, we highlight the power of in situ optical imaging in revealing new findings from photofunctional materials, including (1) revealing the spatiotemporal heterogeneities of chemical reactivities at a single (sub)particle level and (2) visually manipulating the photophysical and photochemical process of photofunctional materials at the micro/nanoscale. Finally, we conclude with our opinions on easily ignored aspects during in situ optical imaging of photofunctional materials and the future directions in this field.