- Substituted 9-Diethylaminobenzo[ a]phenoxazin-5-ones (Nile Red Analogues): Synthesis and Photophysical Properties
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Nile Red is a benzo[a]phenoxazone dye containing a diethylamino substituent at the 9-position. In recent years, it has become a popular histological stain for cellular membranes and lipid droplets due to its unrivaled fluorescent properties in lipophilic environments. This makes it an attractive lead for chemical decoration to tweak its attributes and optimize it for more specialized microscopy techniques, e.g., fluorescence lifetime imaging or two-photon excited fluorescence microscopy, to which Nile Red has never been optimized. Herein, we present synthesis approaches to a series of monosubstituted Nile Red derivatives (9-diethylbenzo[a]phenoxazin-5-ones) starting from 1-naphthols or 1,3-naphthalenediols. The solvatochromic responsiveness of these fluorophores is reported with focus on how the substituents affect the absorption and emission spectra, luminosity, fluorescence lifetimes, and two-photon absorptivity. Several of the analogues emerge as strong candidates for reporting the polarity of their local environment. Specifically, the one- and two-photon excited fluorescence of Nile Red turns out to be very responsive to substitution, and the spectroscopic features can be finely tuned by judiciously introducing substituents of distinct electronic character at specific positions. This new toolkit of 9-diethylbenzo[a]phenoxazine-5-ones constitutes a step toward the next generation of optical molecular probes for advancing the understanding of lipid structures and cellular processes.
- Hornum, Mick,Mulberg, Mads W.,Szomek, Maria,Reinholdt, Peter,Brewer, Jonathan R.,Wüstner, Daniel,Kongsted, Jacob,Nielsen, Poul
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supporting information
p. 1471 - 1488
(2021/01/13)
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- Process for preparing N,N-disubstituted p-phenylenediamine derivatives
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A process for preparing an N,N-disubstituted p-phenylenediamine of the formula STR1 wherein R1 is alkyl of 1-6 C atoms, R2 is alkyl of 1-6 C atoms or alkyl of 1-6 C atoms which is substituted by OH, lower alkoxy, a sulfo group or an alkylsulfonamido group and R3 is hydrogen or lower alkyl or an acid addition salt thereof, comprises adding an alkyl nitrite, as a nitrosation agent, to an aqueous, acid suspension of the corresponding aniline derivative of the formula STR2 thereby forming the corresponding N,N-disubstituted p-nitroso-aniline, and subsequently hydrogenating the latter without isolation thereof from the reaction mixture.
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