Seminaphthofluorones are a family of water-soluble, low molecular weight, NIR-emitting fluorophores
? 2008 by The National Academy of Sciences of the USA. Freely available online through the PNAS open access option
A readily accessible new class of near infrared (NIR) molecular probes has been synthesized and evaluated. Specific fluorophores in this unique xanthene based regioisomeric seminaphthofluorone dye series exhibit a combination of desirable characteristics including (i) low molecular weight (339 amu), (ii) aqueous solubility, and (iii) dual excitation and emission from their fluorescent neutral and anionic forms. Importantly, systematic changes in the regiochemistry of benzannulation and the ionizable moieties afford (iv) tunable deep-red to NIR emission from anionic species and (v) enhanced Stokes shifts. Anionic SNAFR-6, exhibiting an unusually large Stokes shift of ÷200 nm (5,014 cm?1) in aqueous buffer, embodies an unprecedented fluorophore that emits NIR fluorescence when excited in the blue/green wavelength region. The successful use of SNAFR-6 in cellular imaging studies demonstrates proof-of-concept that this class of dyes possesses photophysical characteristics that allow their use in practical applications. Notably, each of the new fluorophores described is a minimal template structure for evaluation of their basic spectral properties, which may be further functionalized and optimized yielding concomitant improvements in their photophysical properties.