Correlation between the molecular structure and trans ↔ cis isomerization characteristics of azobenzenes

Abstract

Photochemical and thermal isomerization of various azobenzenes was systematically investigated to understand the correlation between the molecular structure and trans ↔ cis isomerization characteristics of azobenzenes. A blue shift in - * absorption band of ortho-alkylated azobenzenes (1o and 2o) was observed together with a reduction in molar extinction coefficient (  ) in comparison with both meta-alkylated azobenzenes (4m and 5m) and 7p lacking the meta and ortho substituents. For orthoalkylated azobenzene, photochemical trans-to-cis isomerization and thermal back cis-to-trans isomerization in solution occurred slowly when compared with 4m, 5m and 7p. The half-life time of the cis form of 2o was found to be 380 h, which is about 8-50 times longer than those of comparable 4m, 5m (43-13 h) and 7p (7 h). Furthermore, comparison of the molecular structure and isomerization characteristics of azobenzene thiol (2o and 5m) self-assembled monolayers on flat gold surfaces indicates that the trans-to-cis photoconversion in monolayer systems is influenced by steric hindrance and strong intermolecular interaction between azobenzene units. azobenzene, isomerization, lifetime of cis form, molecular structure

From China to the world: Science China Chemistry celebrates the International Year of Chemistry

“…"A blue shift in - * absorption band of ortho-alkylated azobenzenes (1o and 2o) was observed together with a reduction in molar extinction coefficient (  ) in comparison with both meta-alkylated azobenzenes (4m and 5m) and 7p lacking the meta and ortho substituents" (Figure 4). "The half-life time of the cis form of 2o was found to be 380 h, which is about 850 times longer than those of comparable 4m, 5m (4313 h) and 7p (7 h)" [27]. Watson Loh and Cesar Brinatti highlighted recent work in using calorimetry to gain molecular insights on association processes in surfactant-polymer mixtures [35].…”

“…"Lichens are unique individuals which have been widely Heather F. Greer [16] Fengjiao Yu [16] Carol A. Fierke [18] Xiaomu Guan [18] Mina Han [27] Maria Luisa Cerón [30] Eleonora Echegaray [30] Bárbara Herrera [30] Soledad Gutiérrez-Oliva [30] Xiuting Li [31] Ada Yonath [34] Fang Liu [38] Figure 2 Photos of some female authors in the special issue on IYC 2011. used in traditional medicines," M. Iqbal Choudhary, Atta-ur-Rahman, and coworkers indicated [23]. They presented their findings of new antiglycation and enzyme inhibitors from the lichens species Parmotrema cooperi collected from Nepal at the altitude of 16001700 meters.…”

Azobenzene isomerization in condensed matter: lessons for the design of efficient light-responsive soft-matter systems

“…Substitutions can also have a stark effect on the stability of the cis isomer, therefore also having an effect on the rate of cis to trans reverse isomerization. 53 One key example of this is so-called 'push-pull' azobenzenes, which have electron donating and electron withdrawing substitutions in opposing para positions (4-and 4 0 -positions) on the azobenzene rings. This ''push-pull'' arrangement can lead to the quantum yield of trans to cis isomerization becoming significantly less than that of the reverse cis to trans process.…”

Kinetics of UV Radiation-Induced Fast Collapse and Recovery in Thermally Cycled and Rehydrated Light- and Thermo- Double-Responsive Copolymer Films Probed by In Situ Neutron Reflectivity

“…In addition to polymers sensitive to temperature, polymers sensitive to light have also attracted plenty of attention due to their immediate response and remote control capability. − Among all reported functional groups with light-responsive behavior, azobenzene has been broadly studied. − After exposure to UV radiation, azobenzene will isomerize from a trans - to a cis -state, inducing enhanced hydrophilicity and polarity of the polymers containing azobenzene. When the UV radiation is removed, azobenzene returns back to its trans -state. , Based on these unique characteristics, the azobenzene components are added to the thermo-responsive polymers to improve their hydrophilicity in the related copolymers under UV radiation. − Thus, such kind of double-responsive copolymers can be used as drug carriers. − In addition, when the double-responsive copolymer is cross-linked onto fabrics, not only the cleaning ability of cotton fabrics , but also the UV shielding capability of silk fabrics was improved …”