pcStar is a monomeric fluorescent protein that can be irreversibly photoconverted from an initial green fluorescent form to a red fluorescent form upon UV irradiation. The green fluorescent form has an excitation peak of 505nm and an emission peak of 515nm, while the red fluorescent form has an excitation peak of 567nm and an emission peak of 579nm in vitro. pcStar is an artificial derivative of the naturally occurring fluorescent protein encoded by the Lobophyllia hemprichii EosFP gene (GenBank:AY765217), derived by mutagenesis of mEos3.2; it contains the amino acid substitutions D28E, L93M, and N166G relative to mEos3.2. pcStar shows high photoconversion contrast, high labeling density, and a fast on-switching rate (FBrf0245368).