QAQ dichloride (100 μM) does not cross the membrane and can be injected into cells through a micropipette to photosensitize a single cell and afford subcellular control of action potential propagation. It blocks Shaker-IR current in the trans configuration and unblocks it in the cis configuration [1]. QAQ dichloride can be used to develop red-shifted derivatives of QAQ wihch are powerful doubly charged photochromic blockers.These derivatives allow for remote control of K v and Na v channel conductance with light and offer the opportunity to silence neuronal activity reversibly [2].