Synthesis of Small Fluorescent Molecules and Evaluation of Photophysical Properties.

A series of aniline-based fluorophores were newly synthesized. To increase their fluorescence quantum yields, it was particularly important to substitute 3,3,3-trifluoroprop-1-enyl (TFPE) groups next to the amino group to benefit from an extended π-electron delocalization. Among these, 5-CN-2-TFPE-aniline was found to behave as an excellent fluorophore with a reasonable fluorescence quantum yield of 0.89 even in aqueous solution. l-Alanine peptide, a nonfluorescent analogue of 5-CN-2-TFPE-aniline, was synthesized and successfully employed as an enzyme probe to detect aminopeptidase N activity.