The second near-infrared (NIR-II) spectrum in the 1000-1700 nm range offers many advantages for deep-tissue imaging and modulation owing to its reduced light scattering, absorption, and tissue autofluorescence. It has been demonstrated by us and many other groups that fluorescence imaging in the NIR-II window can resolve the fine structures and fast hemodynamics of cerebral vessels in the mouse brain through the intact scalp and skull. We are developing NIR-II light-absorbing conjugated polymers for modulating brain activity with neuron-type specificity, thus enabling infrared optogenetics in freely behaving and socially interactive animals in an implant-free and tether-free manner. Read our Nature Photonics and Nature Biomedical Engineering papers to learn more. Stay tuned for our recently accepted paper in Nature Biomedical Engineering (2021)!