A conformational switching of bis(zinc octaethylporphyrin) was observed, for the first time, in a Langmuir-Schaefer film as a consequence of appropriate host-guest interactions. The spectral changes are completely reversible and the high sensitivity (similar to 20 ppb) and specificity for aromatic amines open up interesting prospects of this functional material as a performing sensor for amines. (c) 2012 Elsevier Inc. All rights reserved.