Indolizine–Squaraines: NIR Fluorescent Materials with Molecularly Engineered Stokes Shifts

Louis E. McNamara, Tana A. Rill, Aron J. Huckaba, Vigneshraja Ganeshraj, Jacqueline Gayton, Rachael A. Nelson, Emily Anne Sharpe, Amala Dass, Nathan I. Hammer, Jared H. Delcamp

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


The development of deep red and near infrared emissive materials with high quantum yields is an important challenge. Several classes of squaraine dyes have demonstrated high quantum yields, but require significantly red-shifted absorptions to access the NIR window. Additionally, squaraine dyes have typically shown narrow Stokes shifts, which limits their use in living biological imaging applications due to dye emission interference with the light source. Through the incorporation of indolizine heterocycles we have synthesized novel indolizine squaraine dyes with increased Stokes shifts (up to >0.119 eV, >50 nm increase) and absorptions substantially further into the NIR region than an indoline squaraine benchmark (726 nm versus 659 nm absorption maxima). These materials have shown significantly enhanced water solubility, which is unique for squaraine dyes without water-solubilizing substituents. Absorption, electrochemical, computational, and fluorescence studies were undertaken and exceptional fluorescence quantum yields of up 12 % were observed with emission curves extending beyond 850 nm.

Original languageEnglish
Pages (from-to)12494-12501
Number of pages8
JournalChemistry - A European Journal
Issue number51
StatePublished - Sep 12 2017

Bibliographical note

Funding Information:
T.R. and E.A.S. acknowledge funding support from the University of Mississippi Sally Barksdale Honors College. L.E.M., T.R., A.J.H., J.G., E.A.S., R.A.N., N.I.H. and J.H.D. acknowledge support from NSF OIA EPS Track 2 (1539035) program. thank NSF Grant 1255519.

Publisher Copyright:
© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim


  • NIR dyes
  • emissive materials
  • fluorescence quantum yield
  • indolizine
  • squaraine

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry


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