“…In the past years, a huge amount of photoswitchable fluorophores has been developed including photochromic compounds, [54][55][56] conventional organic fluorophores, [31,35,36,40,47,57] caged fluorescent dyes, [58] push-pull fluorophores, [59] and a variety of photoswitchable FP. [4,[60][61][62] In the following, we restrict our considerations to irreversible photoswitching of photoactivatable or photoconvertible FP and reversible photoswitching of FP and synthetic organic fluorophores since they are currently the most promising candidates for single-molecule based localization microscopy.…”