mEos4b 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 516nm, while the red fluorescent form has an excitation peak of 570nm and an emission peak of 580nm in vitro. mEos4b is an artificial derivative of the naturally occurring fluorescent protein encoded by the Lobophyllia hemprichii EosFP gene (GenBank:AY765217). It contains the mutations K9R, F34Y, S39T, A69V, I102N, H158E, Y189A and C195A relative to mEos2 (PMID:25581799).