The need for NIR fluorescent dyes is widely accepted for imaging and communications applications. Cyanines are a commonly used family of dyes for biological imaging due their tunability, often rapid synthesis, ease of bioconjugation, intense molar absorptivities and strong NIR emissions. Since the invention of indocyanine green (ICG), many efforts have been made to improve on the design achieving farther red-shifted dyes with larger quantum yields and enhanced Stokes shifts. Recently, our group published a series of squaraine dyes using the indolizine heterocycle as a donor in place of the indolenine donor. The indolizine donor allows for red-shifts farther into the NIR region due to the proaromaticity of the indolizine in generating an aromatic stabilized pyridinium ring in the excited-state. Additionally, an enhanced Stokes shift is observed to enable high resolution imaging. These squaraine dyes will be discussed in addition to a series of recently prepared cyanine dyes utilizing indolizine donors with a focus on structure-property relationships concerning the effects on the absorption, emission, and quantum yields.

NIR fluorescent indolizine-squaraine and indolizine-cyanine dyes

255th National Meeting (2018)

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