3986-52-5Relevant articles and documents
Trans–cis isomerization energies of azopyridines: a calorimetric and computational study
Zhu, Men,Yu, Lian
, p. 463 - 469 (2018)
Azobenzenes undergo reversible trans–cis photo-isomerization and have been studied extensively as photo-responsive materials. Despite their similar photochemistry, azopyridines have received relatively little attention; for example, their isomerization energies are presently unknown. In comparison with azobenzenes, azopyridines offer additional opportunities for materials design through hydrogen bonding and coordination chemistry. Here we report the isomerization energies for all three symmetrical azopyridines (i.e., the 2,2′-, 3,3′-, and 4,4′-isomers) through a combined experimental and computational study. Heat of isomerization was measured in the liquid state, with o-terphenyl introduced to suppress crystallization. We obtain ?Eiso?=?25.2?±?0.6, 42.6?±?0.6, and 35.0?±?1.8?kJ?mol?1 for 2,2′, 3,3′, and 4,4′-azopyridine, respectively. For azobenzene, we obtain ?Eiso?=?47.0?±?1.3?kJ?mol?1, in agreement with the literature value and validating our method. Theoretical calculations yielded gas-phase ?Eiso in reasonable agreement with experiment and explain the low isomerization energy of 2,2′-azopyridine on the basis of a low-energy cis conformer. Because of the smaller van der Waals volume of the pyridine N relative to the phenyl CH, the two aromatic rings in the cis isomer can approach closer to coplanarity, leading to greater π-conjugation and lower conformational energy.
Photoresponsive metallo-hydrogels based on visual discrimination of the positional isomers through selective thixotropic gel collapse
Fang, Weiwei,Liu, Xiyu,Lu, Zhengwei,Tu, Tao
, p. 3313 - 3316 (2014)
Incorporating the visual discrimination of 2,2′-bipyridine and self-healing properties, a novel photo-switchable metallo-hydrogel system is fabricated using a pincer-type Cu(II) complex and 2,2′-azopyridine. The Royal Society of Chemistry 2014.
Photoreponsive Crown Ethers. Part 7. Proton and Metal Ion Catalyses in the cis-trans Isomerisation of Azopyridines and an Azopyridine-bridged Cryptand
Shinkay, Seiji,Kouno, Takeshi,Kusano, Yumiko,Manabe, Osamu
, p. 2741 - 2748 (2007/10/02)
A 2,2'-azopyridine-bridged crown ether (5) has been synthesised for the purpose of controlling the ion-binding functions by an on-off light switch mechanism.Since the trans-azopyridine moiety of compound (5) is vertically over the crown ether ring and the photoisomerised cis-azopyridine moiety of (5) is almost parallel to the crown ether plane, it would be expected that only the pyridine nitrogen of trans-(5) are capable of co-ordinating to metal ions bound into the crown ether ring.The thermal isomerisation of cis-2,2'-azopyridine to trans-2,2'-azopyridine was speeded up either by protonation of the pyridine nitrogen or by complexation with heawy-metal ions (e.g.Cu2+, Ni2+, and Co2+).Similarly, the thermal isomerisation of cis-(5) to trans-(5) was speeded up by protonation of azopyridine, but the metal ion catalysis was observed only for the metal ions which were bound into the crown ether ring (e.g.Cu2+ and Pb2+).The result of solvent extraction of alkali-metal ions with (5) was very similar to that with an azobenzene-bridged crown ether (1), indicating that the 2,2'-azopyridine-bridge of (5) has almost no effect on the extraction of alkali-metal ions.On the other hand, trans-(5) was capable of extracting considerable amounts of heavy-metal ions (Cu2+, Ni2+, CXo2+, and Hg2+), whereas photoisomerised cis-(5) scarcely extracted these metal ions.Such a difference in the extractability was not observed between trans-(1) and photoisomerised cis-(1).Neither the trans- nor the cis-form of 6,6'-bis(morpholinocarbonyl)-2,2'-azopyridine could extract these metal ions under comparable extraction conditions.These results suggest that pyridine nitrogens of trans-(5) are directed towards the crown ether plane so as to co-ordinate to metal ions in the crown ether ring, whereas those of cis-(5) have no such coordination ability due to the distorted configuration.Therefore, compound (5) would act as a 'photoresponse cryptand' for heavy metal ions.
