The spun film of zinc(II) 1,4,8,11,15,18,22,25-octabutoxy-phthalocyanine was investigated as optical sensor for amine vapors. The enhancement of the Q band absorbance at 750 nm was attributed to the coordination of amine to the central zinc ion. Effects of the amine structure on the sensing properties were investigated to elucidate the sensing mechanism. Sensitivity and response speed of the sensor are influenced by the gas phase basicity and the steric hindrance effect of the amine. Among the six-carbon amines studied, n-hexylamine shows the highest sensitivity and the fastest response, followed by dipropylamine, and then the tertiary triethylamine. For primary amines, the sensitivity and the response speed increase as length of the alkyl chain increases. The response time for 1000 ppm n-hexylamine is 11s, and that for methylamine is 440 s. The response signal Delta A(750) is found to be proportional to the amine concentration for n-butylamine in the 5-40 ppm range, with the sensitivity S = 0.0009/ppm. (C) 2007 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.