Synthesis and characterization of bis(4-amino-2-bromo-6-methoxy)azobenzene derivatives

• David Martínez-López,
• Amirhossein Babalhavaeji,
• Diego Sampedro and
• G. Andrew Woolley

Beilstein J. Org. Chem. 2019, 15, 3000–3008, doi:10.3762/bjoc.15.296

• in particular can form azonium ions under physiological conditions and exhibit red-light photoswitching. Here, we report the synthesis and characterization of two bis(4-amino-2-bromo-6-methoxy)azobenzene derivatives. These compounds form red-light-absorbing azonium ions, but only under very acidic

• conditions (pH < 1). While the low pKa makes the azonium form unsuitable, the neutral versions of these compounds undergo trans-to-cis photoisomerization with blue-green light and exhibit slow (τ1/2 ≈ 10 min) thermal reversion and so may find applications under physiological conditions. Keywords: azobenzene

• ; azonium; molecular switches; ortho substitution; photoisomerization; photoswitch; visible light; Introduction The application of photoswitches to control biological targets has been a driving force for the development of photoswitches that operate at wavelengths that are compatible with cells and tissues

A bisazobenzene crosslinker that isomerizes with visible light

• Subhas Samanta,
• Harris I. Qureshi and
• G. Andrew Woolley

Beilstein J. Org. Chem. 2012, 8, 2184–2190, doi:10.3762/bjoc.8.246

• dependent below pH 6.0 (Figure 2b). A band corresponding to the azonium species [27] near 600 nm is evident at pH 5 and this does not appear to change upon irradiation. At lower pH values the spectrum undergoes further changes with enhanced absorbance from 530–700 nm consistent with the formation of a

Cyclodextrin-induced host–guest effects of classically prepared poly(NIPAM) bearing azo-dye end groups

• Gero Maatz,
• Arkadius Maciollek and
• Helmut Ritter

Beilstein J. Org. Chem. 2012, 8, 1929–1935, doi:10.3762/bjoc.8.224

• , a large bathochromic (red) shift takes place, due to the protonation of the azo dye of 6 [17]. As illustrated in Figure 1A this red shift corresponds to an increase of the absorption up to 500–550 nm, whereas the band at 420 nm decreases. Thus, the protonated azonium tautomer is considered to be the

• . Hereby, a strong blue shift in the absorption spectra was observed (Figure 1B). As mentioned above, the absorption spectra of 6 after protonation indicate the formation of the azonium structure (Figure 1A). The subsequent complexation of this protonated azo dye with RAMEB-CD causes a hypsochromic shift

• . This strongly indicates that, due to the presence of RAMEB-CD, a shift of the equilibrium from the azonium to the amonium form of the azo dye takes place. Consequently, the azo group in 6 is supramolecularly protected from protonation by the surrounding CD ring, while the free dimethylamino group is

Molecular rearrangements of superelectrophiles

• Douglas A. Klumpp

Beilstein J. Org. Chem. 2011, 7, 346–363, doi:10.3762/bjoc.7.45

• nitrogen atom. In the case of α-isomer 108, the developing azonium cation may be stabilized by resonance interaction with the phenyl group of 111. However, with the β-isomer 109 the developing azonium cation is located next to the pyridinium ring 116. Evidently, structure 116 is destabilized by the