Longdaysin is primarily used in biological research to study the regulation of circadian rhythms. It functions as an inhibitor of casein kinase I (CKI), which plays a crucial role in the timing mechanisms of the circadian clock. By modulating CKI activity, Longdaysin helps researchers investigate the molecular pathways that control daily biological cycles in cells and organisms. This compound is particularly valuable in experiments aimed at understanding how disruptions in circadian rhythms can affect health and disease, potentially leading to insights into treatments for sleep disorders, metabolic conditions, and other circadian-related issues. Its application extends to screening assays and pharmacological studies focused on identifying new therapeutic targets for circadian rhythm modulation.