Photochromism and Thermochromism of Zeolite Spramolecules

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(1)Published in J.Phys.Org.Chem.18, 994-1000 (2005) : The half-life (τ_<1/2>) for thermal isomerization of cis-4-hydroxyazobenzene (c-HOAB) to its trans isomer is highly dependent on the solvent used. For non-aromatic solvents, the cis isomer is extremely unstable at 293 K (τ_<1/2> < 1 min in methanol and acetonitrile ; 6 min in cyclohexane), while the cis isomer is surprisingly stable in benzene (τ_<1/2> = 125 min). However, addition of hydrogen chloride and triethylamine in benzene causes a remarkable decrease in τ_<1/2>. On the basis of ab initio molecular orbital calculations of the binding energies and the optimum structures of c-HOAB-solvent complexes, a mechanism for the thermal cis-to-trans isomerization reaction involving hydrogen-bonded dimers and complexes is suggested.(2)Published in Chem.Phys.Lett., 408, 197-204 (2005) : To elucidate the stable structures and electronic properties of hydrogen-bonded 4-hydroxyazobenzene (HOAB) dimers, we performed ab initio molecular orbita … More l calculations based on the density functional theory. The obtained stable structures and total energies for the fifteen types of dimers indicate that the trans-trans HOAB dimers are at least 10 kcal/mol more stable than the other cis-cis, cis-trans and trans-cis dimers. In addition, it was found that the dimer of tautomerized trans-HOAB has similar stability to the trans-trans HOAB dimers, suggesting that the tautomerized trans-HOAB dimer contributes to the unique photochemical and spectroscopic behavior of HOAB.(3)Published in Res.Chem.Intermed., 30, 181-190 (2004) : In the photostationary state, the cis/traps isomer ratio of azobenzene and 3,3'-dimethylazobenzene adsorbed in zeolite NaY increases significantly to ca. 90/10 in contrast to the reaction in cyclohexane. However, for azobenzene-4,4'-dicarboxylic acid diethyl ester the formation of the cis isomer is remarkably suppressed to ca. 30%. On the basis of ab initio MO calculations, it is suggested that electrostatic interaction between these azobenzenes and the metal ions in zeolite nanocavities regulates the cis-trans photoisomerization process. In addition, it is found that the photoisomerization behavior of azobenzenes adsorbed on silica gel is similar to that in NaY.(4)Research related to this study was reviewed in Handbook of Photochemistry and Photobiology (2003) and also Encyclopedia of Nanoscience and Nanotechnology (2004). Less