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Highly Fluorescent Dyes Containing Conformationally Restrained Pyrazolylpyrene (Pyrazoolympicene) Chromophore.

Janusz ZakrzewskiAnna MakalJanusz Zakrzewski
Published in: Molecules (Basel, Switzerland) (2022)
The triflic-acid-promoted cyclization of 1-phenyl-3-(pyren-1-yl)-1 H -pyrazole-4-carbaldehyde afforded a mixture of 9-phenyl-7,9-dihydropyreno (10,1- fg )indazole and 9-phenylpyreno(10,1- fg )indazole-7(9 H )-one, readily separable by column chromatography. Both products contained a rigid six-ringed pyrazoolympicene backbone and exhibited bright fluorescence in chloroform solution and a weak fluorescence in the solid state. DFT and TD DFT calculations revealed that the lowest excited state (S 1 ) of these compounds is populated via HOMO →LUMO π-π * transition. Furthermore, the synthesized compounds behaved as weak bases and their emission spectra showed substantial changes upon protonation. Therefore, they may be of interest for sensing of strongly acidic fluorophore environments.
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