PHOTOCHROMIC AND ELECTROCHEMICAL-BEHAVIOR OF A CROWN-ETHER-DERIVED AZOBENZENE MONOLAYER ASSEMBLY

The photochromism and electrochemical behavior of a Langmuir-Blodgett (LB) monolayer formed by a novel crown-ether-derived azobenzene deriva tive (CAD) are reported. The large crown-ether functionality was intro duced into the CAD molecule as a spacer to provide enough free volume for azobenzene trans-cis isomerization and also as the hydrophilic hea d group for LB film fabrication. The CAD molecules formed a stable mon olayer at the air\water interface which could also be transferred well to solid substrates. The photochemical conversion rate from trans to cis isomers in this azobenzene monolayer reached 76 +/- 4%, showing a great increase compared with that in a simple long-chain fatty acid az obenzene LB film (30%). It is only a little smaller than the value obt ained in solution (86%). The two isomers in the LB films showed signif icantly different electrochemical responses, with the cis isomer being more easily reduced than the trans isomer. The electron transfer rate constant k(s) was also evaluated. The present studies confirmed that the incorporation of a large group can greatly improve the photochromi sm of azobenzene in condensed films and demonstrated the great potenti al of molecular design for controlling the functionality of monolayer assemblies. (C) 1997 Elsevier Science S.A.