Compositions of matter comprising 5-phenoxyalkoxypsoralen compounds and their method of synthesis and use. The compounds are useable to treat diseases or disorders in human or animal subjects, including autoimmune diseases. The compounds inhibit potassium channels, including the Kv1.3 channel and at least some of the therapeutic effects of such compounds may be due at least in part to potassium channel inhibition. In some embodiments, the compounds are more selective for certain potassium channels (e.g., Kv1.3 channels) than other potassium channels (e.g., Kv1.5 channels).