Rational Design of a Near-infrared Fluorescence Probe for Ca2+ Based on Phosphorus-substituted Rhodamines Utilizing Photoinduced Electron Transfer

Shodai Takahashi, Kenjiro Hanaoka, Yohei Okubo, Honami Echizen, Takayuki Ikeno, Toru Komatsu, Tasuku Ueno, Kenzo Hirose, Masamitsu Iino, Tetsuo Nagano, Yasuteru Urano

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)


Fluorescence imaging in the near-infrared (NIR) region (650–900 nm) is useful for bioimaging because background autofluorescence is low and tissue penetration is high in this range. In addition, NIR fluorescence is useful as a complementary color window to green and red for multicolor imaging. Here, we compared the photoinduced electron transfer (PeT)-mediated fluorescence quenching of silicon- and phosphorus-substituted rhodamines (SiRs and PRs) in order to guide the development of improved far-red to NIR fluorescent dyes. The results of density functional theory calculations and photophysical evaluation of a series of newly synthesized PRs confirmed that the fluorescence of PRs was more susceptible than that of SiRs to quenching via PeT. Based on this, we designed and synthesized a NIR fluorescence probe for Ca2+, CaPR-1, and its membrane-permeable acetoxymethyl derivative, CaPR-1 AM, which is distributed to the cytosol, in marked contrast to our previously reported Ca2+ far-red to NIR fluorescence probe based on the SiR scaffold, CaSiR-1 AM, which is mainly localized in lysosomes as well as cytosol in living cells. CaPR-1 showed longer-wavelength absorption and emission (up to 712 nm) than CaSiR-1. The new probe was able to image Ca2+ at dendrites and spines in brain slices, and should be a useful tool in neuroscience research.

Original languageEnglish
Pages (from-to)524-530
Number of pages7
JournalChemistry - An Asian Journal
Issue number4
Publication statusPublished - 2020 Feb 17
Externally publishedYes


  • Calcium
  • Fluorescence
  • Fluorescence spectroscopy
  • Fluorescent probes
  • Neuroscience

ASJC Scopus subject areas

  • Biochemistry
  • Organic Chemistry


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