8-NBD-cGMP
8-NBD-cGMP is a fluorescent analog of cyclic guanosine monophosphate and a potent, membrane-permeable, fluorescent activator of cGMP-dependent protein kinase isozymes I α and I β. 8-NBD-cGMP is barely fluorescent in aqueous solution but fluoresces strongly in hydrophobic environments such as hydrophobic protein binding sites