| Popis: |
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 π-π* absorption band of ortho -alkylated azobenzenes (1o and 2o) was observed together with a reduction in molar extinction coefficient ( e ) in comparison with both meta-alkylated azobenzenes (4m and 5m) and 7p lacking the meta and ortho substituents. For ortho -alkylated 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. |
