Abstract
A series of new 5‐mono‐ and 5,5′‐bisamino‐substituted azothiazole derivatives was synthesized from the readily available diethyl azothiazole‐4,4′‐dicarboxylate. This reaction most likely comprises an initial Michael‐type addition by the respective primary alkyl and aromatic amines at the carbon atom C5 of the substrate. Subsequently, the resulting intermediates are readily oxidized by molecular oxygen to afford the amino‐substituted azothiazole derivatives. The latter exhibit remarkably red‐shifted absorption bands (λ abs=507–661 nm) with high molar extinction coefficients and show a strong positive solvatochromism. As revealed by spectrometric titrations and circular and linear dichroism studies, the water‐soluble, bis‐(dimethylaminopropylamino)‐substituted azo dye associates with duplex DNA by formation of aggregates along the phosphate backbone at high ligand–DNA ratios (LDR) and by intercalation at low LDR, which also leads to a significant increase of the otherwise low emission intensity at 671 nm.
Highlights
Aromatic azo compounds have been extensively investigated with regard to their photophysical and photochromic properties since they are commonly utilized in several different fields.[1]
The known azothiazole diethyl ester 2 g was synthesized by condensation of 2,5-dithiobiurea (3) with ethyl 3-bromopyruvate followed by oxidation of the intermediate hydrazothiazole 4 according to literature procedure.[27d]. The addition of n-butylamine (5 a) to a suspension of 1 and MgCl2 as Lewis acid in THF (Scheme 1)[28] resulted in an immediate color change of the suspension from orange to magenta indicating a drastic bathochromic shift of the absorption maximum caused by significant structural changes in the conjugated aromatic system
The readily available diethyl azothiazole-4,4’-dicarboxylate (2 g) unexpectedly undergoes a Michael-type addition with primary alkyl and aromatic amines at C5, and the intermediates are readily oxidized by molecular oxygen under aerobic conditions to afford novel mono- and bis-substituted 5-alkyl- and 5-phenylamino azothiazole derivatives
Summary
Aromatic azo compounds have been extensively investigated with regard to their photophysical and photochromic properties since they are commonly utilized in several different fields.[1] For example, they are used in solar cells[2] and solar thermal fuels,[3] sensors,[4] photopharmacology,[5] and biomedical applications.[6] they have been incorporated as molecular switches into polymers[7] and carbohydrates[8] as well as into biological systems[9] such as oligonucleotides,[10] peptides, and proteins.[11] And azo derivatives have been used in the design of (photoswitchable) ligands for duplex[12] and quadruplex DNA.[13] Most importantly, azo dyes represent the largest group of colorants with respect to their number and production volume in the chemical industry, mainly because they generally exhibit high molar extinction coefficients and colorfastness.[14] the most commonly employed synthesis of azo dyes by diazotization and azo coupling is not just straightforward but offers a huge structural diversity.[14,15] It is well known that the introduction of different electron-donating and electron-withdrawing substituents into the structure of azobenzene enables a significant variation of color.[14] In this regard, the replacement of one or even both phenyl substitu-
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
