5(6)-TMR C6 maleimide is an excellent replacement to tetramethylrhodamine-5-(and 6)-maleimide. It selectively reacts with thiol groups of peptides, proteins and other biological molecules (such as thiol-modified oligonucleotides and small thiol-containing organic molecules). It might give higher conjugation yield than tetramethylrhodamine-5-(and 6)-maleimide under similar conjugation conditions. 5(6)-TMR C6 maleimide has the spectral properties identical to those of tetramethylrhodamine-5-(and 6)-maleimide, thus all the instrument settings of the tetramethylrhodamine-5-(and 6)-maleimide would be applicable to the applications of 5-TMR C6 maleimide conjugates.