Pyrazole-substituted Near-infrared Cyanine Dyes Exhibit pH-dependent Fluorescence Lifetime Properties

• Published in: Photochemistry and photobiology Vol. 89; no. 2; pp. 326 - 331
• Main Authors: Lee, Hyeran, Berezin, Mikhail Y., Tang, Rui, Zhegalova, Natalia, Achilefu, Samuel
• Format: Journal Article
• Language: English
• Published: United States Blackwell Publishing Ltd 01.03.2013
• Subjects: Acidity; Carbocyanines - chemistry; Dimethyl Sulfoxide; Electron transfer; Electrons; Fluorescence; Fluorescent Dyes - chemistry; Hydrogen-Ion Concentration; Indocyanine Green - analogs & derivatives; Indocyanine Green - chemistry; Organic chemistry; Photochemistry; Physical properties; Pyrazoles - chemistry; Spectrometry, Fluorescence; Spectroscopy, Near-Infrared; Spectrum analysis
• ISSN: 0031-8655; 1751-1097
• DOI: 10.1111/php.12009

Near‐infrared heptamethine cyanine dye is functionalized with pyrazole derivatives at the meso‐position to induce pH‐dependent photophysical properties. The presence of pyrazole unsubstituted at 1N‐position is essential to induce pH‐dependent fluorescence intensity and lifetime changes in these dyes. Replacement of meso‐chloro group of cyanine dye IR820 with 1N‐unsubstituted pyrazole resulted in the pH‐dependent fluorescence lifetime changes from 0.93 ns in neutral media to 1.27 ns in acidic media in DMSO. Time‐resolved emission spectra (TRES) revealed that at lower pH, the pyrazole consists of fluorophores with two distinct lifetimes, which cor‐responds to pH‐sensitive and non‐pH‐sensitive species. In contrast, 1N‐substituted pyrazoles do not exhibit pH response, suggesting excited state electron transfer as the mechanism of pH‐dependent fluorescence lifetime sensitivity for this class of compounds. Pyrazole meso‐substituted heptamethine cyanine dye showed pH‐dependent fluorescence lifetime change within physiological useful range. This novel fluorescent probe is a good candidate for in vivo diagnostics using fluorescence lifetime imaging method.