Optical changes induced in Zn porphyrin solutions and LB films by exposure to amines

The 5,10,15,20-tetrakis[3,4-bis(2-ethylhexyloxy)phenyl]-21H,23H-porphinato zinc(II) (ZnEHO) is highly stable and exhibits a colorful absorption spectrum in the visible range. Exposure of a chloroform solution of ZnEHO to amines is shown to induce changes in the characteristic optical spectrum owing to charge transfer between the amine and the delocalized pi-electron system within the highly conjugated molecule. Solid state Langmuir Blodgett (LB) films containing only ZnEHO are compared to films containing a mixture of ZnEHO and calix[8]arene. The transparent calix[8]arene does not change the optical response but aids the diffusion of the amine gas into the LB films. Atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM) images demonstrate the topological and compositional differences between the samples. The response of the LB films of ZnEHO and calix[8]arene to a variety of different amines demonstrates that this is a good material system for use as an amine sensor. Copyright (c) 2006 Society of Porphyrins & Phthalocyanines.