posted on 2021-12-17, 21:14authored byHeydar Shojaei, Mariano L. Bossi, Vladimir N. Belov, Stefan W. Hell
Two fluorophores
bound with a short photoreactive bridge are fascinating
structures and remained unexplored. To investigate the synthesis and
photolysis of such dyes, we linked two rhodamine dyes via a diazoketone
bridge (−COCN2−) attached to position 5′
or 6′ of the pendant phenyl rings. For that, the mixture of
5′- or 6′-bromo derivatives of the parent dye was prepared,
transformed into 1,2-diarylacetylenes, hydrated to 1,2-diarylethanones,
and converted to diazoketones Ar1COCN2Ar2. The high performance liquid chromatography (HPLC) separation
gave four individual regioisomers of Ar1COCN2Ar2. Photolysis of the model compoundC6H5COCN2C6H5in
aqueous acetonitrile at pH 7.3 and under irradiation with 365 nm light
provided diphenylacetic acid amide (Wolff rearrangement). However,
under the same conditions, Ar1COCN2Ar2 gave mainly α-diketones Ar1COCOAr2.
The migration ability of the very bulky dye residues was low, and
the Wolff rearrangement did not occur. We observed only moderate fluorescence
increase, which may be explained by the insufficient quenching ability
of diazoketone bridge (−COCN2−) and its transformation
into another (weaker) quencher, 1,2-diarylethane-1,2-dione.