title: Near-infrared-emitting squaraine dyes with high 2PA cross-sections for multiphoton fluorescence imaging.
abstract: Designed to achieve high two-photon absorptivity, new near-infrared (NIR) emitting squaraine dyes, (E)-2-(1-(2-(2-methoxyethoxy)ethyl)-5-(3,4,5-trimethoxystyryl)-1H-pyrrol-2-yl)-4-(1-(2-(2-methoxyethoxy)ethyl)-5-(3,4,5-trimethoxystyryl)-2H-pyrrolium-2-ylidene)-3-oxocyclobut-1-enolate (1) and (Z)-2-(4-(dibutylamino)-2-hydroxyphenyl)-4-(4-(dibutyliminio)-2-hydroxycyclohexa-2,5-dienylidene)-3-oxocyclobut-1-enolate (2), were synthesized and characterized. Their linear photophysical properties were investigated via UV-visible absorption spectroscopy and fluorescence spectroscopy in various solvents, while their nonlinear photophysical properties were investigated using a combination of two-photon induced fluorescence and open aperture z-scan methods. Squaraine 1 exhibited a high two-photon absorption (2PA) cross-section (δ2PA), ∼20 000 GM at 800 nm, and high photostability with the photochemical decomposition quantum yield one order of magnitude lower than Cy 5, a commercially available pentamethine cyanine NIR dye. The cytotoxicity of the squaraine dyes were evaluated in HCT 116 and COS 7 cell lines to assess the potential of these probes for biomedical imaging. The viability of both cell lines was maintained above 80% at dye concentrations up to 30 μM, indicating good biocompatibility of the probes. Finally, one-photon fluorescence microscopy (1PFM) and two-photon fluorescence microscopy (2PFM) imaging was accomplished after incubation of micelle-encapsulated squaraine probes with HCT 116 and COS 7 cells, demonstrating their potential in 2PFM bioimaging.
authors.affiliation: Department of Chemistry and ‡CREOL, The College of Optics and Photonics, University of Central Florida , P.O. Box 162366, Orlando, Florida 32816-2366, United States.
authors.forename: Hyo-Yang
authors.initials: HY
authors.lastname: Ahn
authors.forename: Sheng
authors.initials: S
authors.lastname: Yao
authors.forename: Xuhua
authors.initials: X
authors.lastname: Wang
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Belfield
mesh_terms: D000818:Animals; D019556:COS Cells; D002470:Cell Survival / Q000187:drug effects; D002522:Chlorocebus aethiops; D003503:Cyclobutanes / Q000737:chemistry* / Q000633:toxicity; D005456:Fluorescent Dyes / Q000737:chemistry* / Q000633:toxicity; D045325:HCT116 Cells; D006801:Humans; D008823:Micelles; D008856:Microscopy, Fluorescence; D010636:Phenols / Q000737:chemistry* / Q000633:toxicity; D017785:Photons; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D003503:Cyclobutanes; D005456:Fluorescent Dyes; D008823:Micelles; D010636:Phenols; C480596:squaraine; D014867:Water