CROWNED AND LIQUID-CRYSTALLINE PHTHALOCYANINES AS GAS-SENSOR MATERIALS

Semiconducting films of crown-ether substituted metal-free phthalocyan ines are shown to have unique properties of fast response and reversal to NO2 at room temperature. Increasing the size of the crown ring or complexing the phthalocyanine with Cu(II) gives slower responses. Comp lexing the crown-ether rings with simple metal salts leads to very rap id reversible conductivity decreases in 1-5 ppm NO2 at room temperatur e. Discotic liquid-crystal phases of octaoctyl phthalocyanine also res pond rapidly and reversibly to NO2. The origins of these effects are d iscussed with reference to reduced local polarizability, increased mol ecular separation and improved molecular assembly, and experiments exp loring the influence of molecular design and crystal engineering on th ese sensing properties are described.