Near-infrared-emitting squaraine dyes with high 2PA cross-sections for multiphoton fluorescence imaging

Hyo Yang Ahn, Sheng Yao, Xuhua Wang, Kevin D. Belfield

Research output: Contribution to journalArticlepeer-review

84 Scopus citations


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 ( 2PA), ∼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.

Original languageEnglish (US)
Pages (from-to)2847-2854
Number of pages8
JournalACS Applied Materials and Interfaces
Issue number6
StatePublished - Jun 27 2012
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General Materials Science


  • and two-photon fluorescence microscopy
  • bioimaging
  • linear and nonlinear optical properties
  • near infrared (NIR) dyes
  • squaraine


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