Trans-cis isomerization of crown ether-substituted azobenzene amphiphiles in Langmuir-Blodgett membranes

The photochemical and thermal isomerization of crown ether-substituted azobenzene amphiphiles were studied in Langmuir-Blodgett (LB) membrane and in solution. The photoisomerization of the azobenzene amphiphiles from trans to cis form tended to be suppressed in LB membrane as compared with those in solution. The cis-trans ratio at the photostationary state under UV light irradiation depended strongly on the chemical structure of the amphiphiles. The trans-cis isomerization was not fully reversible in the LB membranes because the azobenzene amphiphiles are highly densely packed. However, the isomerization reaction was fully reversible in the case of relatively loosely-packed LB membranes. In both membranes, the thermal isomerization from cis to trans form followed first-order kinetics.