tdimer2(12) is a red fluorescent protein with an excitation peak of 552nm and an emission peak of 579nm in vitro. It is an artificial derivative of the naturally occurring fluorescent protein encoded by the Discosoma drFP583 gene (GenBank:AF168419; AAF03369), consisting of a tandem dimer of the dimer2 fluorescent protein linked by a 12 residue linker (PMID:12060735).