Thin films (2-50 nm) of unsubstituted and 1,4-octa-alkyl substituted zinc phthalocyanines were investigated using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, whereas the alkyl chains are C4H7, C7H13, C10H19. The absorption bands in the whole spectral range are discussed. We observe distinct differences in the spectra between the alkyl substituted Phthalocyanine (Pc) compounds. In contrast to PcZn and (but)(8)PcZn, the spectra of (hep)(8)PcZn and (dec)(8)PcZn show two additional features in the spectral range between 3700 and 3000 cm(-1), which are discussed in detail. (c) 2005 Elsevier B.V. All rights reserved.