A platinum(II) complex Pt(phen)C CC6H4CHO has been demonstrated as a highly selective phosphorescent chemodosimeter for cysteine and homocysteine. Upon addition of homocysteine or cysteine to its acetonitrile-water solution, an evident luminescent color variation from green to orange was observed. This red-shift of phosphorescence emission could be attributed to formation of a thiazinane through a selective reaction of aldehyde group of Pt(phen)C CC6H4CHO with cysteine/homocysteine, which was con. rmed by H-1 NMR investigation and density functional theory (DFT) calculations. The further selectivity investigation indicates that it displays high selectivity for homocysteine and cysteine, and therefore can be utilized as cysteine/homocysteine phosphorescent chemodosimeter. (C) 2008 Elsevier B.V. All rights reserved.