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Paper | Special issue | Vol 70, No. 1, 2006, pp.345-354
Published online, 6th October, 2006
DOI: 10.3987/COM-06-S(W)32
Dual Fluorescence Spectra of 1-Hydroxyindoles with Various C-C-Nb Side Chains at 3-Position in Methanol

Kunihiro Tokumura,* Akio Hayashi, Kenta Imai, and Masanori Somei*

*Division of Pharmaceutical Sciences, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa, Ishikawa 920-1192, Japan


Almost the same ultraviolet absorption spectra with a broad peak at 292-294 nm and a shoulder peak at 275 nm were observed for methanol solutions of 1-hydroxyindoles with various C-C-Nb side chains at 3-position such as 1-hydroxy-Nb-methoxycarbonyltryptamine (1), Nb-acetyl-1-hydroxytryptophan methyl ester (2), N,N-dimethyl-1-hydroxyindole-3-acetamide (3), and 1-hydroxy-Nb-pivaloyltryptamine (4). Dual fluorescence excitation and emission spectra resulting from 1La1A and 1Lb1A fluorescence emissions were observed for these 1-hydroxyindoles (1 - 4). Excitation spectra were found to be dependent on observing wavelength of broad fluorescence emission spectra (λmax = 346-350 nm for 1, 2, and 3; λmax = 366 nm for 4). Dual fluorescence behaviors can be explained by the fact that 1La state locates slight below 1Lb state, and it is supported by time-dependent density functional theory calculations of 1 - 4 in methanol. It is noteworthy that dual fluorescence behaviors are delicately modified by C-C-Nb side chain at 3-position of indole ring.