Ultrathin bi-nuclear (cobalt-iron) phthalocyanine, (Co-Fe)Pc films (thickness: ∼20 nm) were grown on (0 0 0 1) Al 2O 3 substrates by molecular beam epitaxy. These films showed very high mobility ∼110 cm 2 V -1 s -1 at room temperature, which are nearly two orders of magnitude higher as compared to the pure CoPc and FePc films prepared under identical conditions. We demonstrated that due to high mobility of bi-nuclear phthalocyanine films, they exhibit enhanced response for chlorine (Cl 2) gas as compared to pure CoPc and FePc films. © 2012 Elsevier B.V. All rights reserved.