Chem. Pharm. Bull., 53(7),750-758, July 2005

Regular Articles

Improvement of Fluorescence Characteristics of Coumarins: Syntheses and Fluorescence Properties of 6-Methoxycoumarin and Benzocoumarin Derivatives as Novel Fluorophores Emitting in the Longer Wavelength Region and Their Application to Analytical Reagents

Chiyomi MURATA,^a Toshinobu MASUDA,^a Yasuko KAMOCHI,^a Kenichiro TODOROKI,^b Hideyuki YOSHIDA,^b Hitoshi NOHTA,^b Masatoshi YAMAGUCHI,^b and Akira TAKADATE^*,a

^a Daiichi College of Pharmaceutical Sciences; 22-1 Tamagawa, Minami-ku, Fukuoka 815-8511, Japan: and ^b Faculty of Pharmaceutical Sciences, Fukuoka University; 8-19-1 Nanakuma, Jonan-ku, Fukuoka 814-0180, Japan. * To whom correspondence should be addressed. e-mail: takadate@daiichi-cps.ac.jp

To improve the fluorescence characteristics, especially emission wavelength, of coumarins, various 3-substituted-6-methoxycoumarin derivatives were synthesized, and then benzocoumarin derivatives were also synthesized in expectation of the shift to the longer wavelength region by the extension of the conjugated system. Their fluorescence properties were investigated spectrophotometrically in acetonitrile and evaluated from the viewpoint of the intramolecular charge transfer (ICT) between push- and pull-substituents in the ground and the excited states. Among them, benzocoumarin derivatives especially fluoresced in the longer wavelength around 540 nm with remarkably large Stokes shifts beyond 10000 cm−1. Using such fluorophores, some novel fluorescence derivatization reagents for carboxylic acids, alcohols, phenols, and amines were preliminarily prepared as an example, and their derivatized products were also found to fluoresce in the longer wavelength region with large Stokes shifts.

Key words fluorescence characteristic; stokes shift; methoxycoumarin; benzocoumarin; intramolecular charge transfer; fluorescence derivatization