Photoswitches are an old idea, one that predates caged compounds. Invented by Erlanger in the 1970s, the reality is they never worked very well for cell physiology, so fell out of favor, even though he made photoswitchable drugs and tethered photoswitchable ligands. Caged compounds worked so well, they blew photoswitches out of the buffer! In 2000 Drew Woolley revived biological application of these photoprobes to control peptide conformation. In 2004 the Berkeley group revived the idea for neuroscience. In 2018 we published our first two papers in this area, includng a study of Hecht's tetrafluoroazobenzene, which we called "4FAB". I wanted to call "FAB4" as I come from Liverpool, but that was not quite right. Importantly, we show for the first time that 2P excitation switches in a chromatically independent manner in both directions.