title: Pyrazole-substituted near-infrared cyanine dyes exhibit pH-dependent fluorescence lifetime properties.
abstract: 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 (1) N-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 (1) N-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, (1) N-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.
authors.affiliation: Department of Radiology, Washington University, St. Louis, MO, USA.
authors.forename: Hyeran
authors.initials: H
authors.lastname: Lee
authors.forename: Mikhail Y
authors.initials: MY
authors.lastname: Berezin
authors.forename: Rui
authors.initials: R
authors.lastname: Tang
authors.forename: Natalia
authors.initials: N
authors.lastname: Zhegalova
authors.forename: Samuel
authors.initials: S
authors.lastname: Achilefu
mesh_terms: D002232:Carbocyanines / Q000737:chemistry*; D004121:Dimethyl Sulfoxide; D004583:Electrons; D005453:Fluorescence; D005456:Fluorescent Dyes / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007208:Indocyanine Green / Q000031:analogs & derivatives* / Q000737:chemistry; D011720:Pyrazoles / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D019265:Spectroscopy, Near-Infrared
chemical_list: D002232:Carbocyanines; D005456:Fluorescent Dyes; C541053:IR 820; D011720:Pyrazoles; D007208:Indocyanine Green; D004121:Dimethyl Sulfoxide