5-4-(Dimethylamino)phenyl-2-benzamidopyrazines: Fluorescent dyes based on Cypridina oxyluciferin

摘要

To clarify the acyl substitution effect on the fluorescent property of Cypridina oxyluciferin analogs, which have the 4-(dimethylamino)phenyl group at C5, we compared the spectroscopic properties of benzamide 1b and its 2,6-dimethylphenyl derivative 1c in various solvents with those of acetamide 1a. Similarity of the fluorescence wavelengths of 1a-c indicates that the π-electronic conjugation in the excited singlet (S_1) state is terminated at the acyl group and that the benzamide moiety in 1b has little effect on modulating the florescence color. The similar fluorescence solvatochromism of 1a-c reveals that their S_1 states have a similar intramolecular charge transfer character. The fact that 1a-c have various fluorescence quantum yields and lifetimes depending on solvent polarity and hydrogen bonding interactions in solutions provides information about the decay processes competing with the fluorescence process in the S_1 states. Among 1a-c, benzamide 1b exhibits the most sensitive variation of the fluorescence intensity depending on the solvent used. Similarity of the fluorescence spectra of 1a-c adsorbed in NaY zeolites was also observed, which indicates that the S_1 states of 1a-c give mobile conformers in the NaY supercages. The relationship between the molecular structures of 1a-c and their spectroscopic properties will provide a guide for designing a new fluorophore based on Cypridina oxyluciferin. Graphical Abstract: Figure not available: see fulltext.