Acidochromic Turn-on 2,4-Diarylpyrano[2, 3-b]indole Luminophores with Solubilizing Groups for A Broad Range of Polarity
Tobias Wilcke, Tobias Glißmann, Arne Lerch, Matthias Karg, Thomas J. J. Müller:
Chemistry Select, 3, 10345-10351 (2018)
doi:10.1002/slct.201802743 
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Acidochromic turn‐on 2,4‐diarylpyrano[2, 3‐b]indole luminophores with different solubilizing groups are readily synthesized in a two‐step process, consisting of a Pd−Cu‐catalyzed domino insertion‐coupling‐cycloisomerization reaction of alkynoyl ortho‐iodo anilides and terminal arylacetylenes furnishing the chromophore, and a desilylation‐alkylation sequence of the 2‐TMS‐ethylthio functionality for introducing solubilizing moieties, i. e. polar and aliphatic swallowtails as well as propylsulfonate potassium. These title compounds are able to cover a broad spectrum of solubility in nonpolar to polar and even aqueous solvent systems. Indeed, the turn‐on fluorescence can be shown to proceed without precipitation in aqueous solvent systems. In addition, a selected pyrano[2, 3‐b]indole forms clusters of 127 nm diameter at high water concentrations as determined by dynamic light scattering.