Periodic Multilayers of Perylene-3,4:9,10-tetracarboxylic Dianhydride and Chloroindium Phthalocyanine: Limitations to Long-Term Stability

The linear optical properties of periodic ultrathin multilayers of perylene-3,4:9,10-tetracarboxylic dianhydride (PTCDA) and chloroindium phthalocyanine (ClInPc) change after exposure to ambient environments. This discoloration extends over a period of months. The B- and Q-bands of CllnPc decrease significantly in intensity, while the PTCDA absorbance spectra are unchanged. CllnPc and PTCDA multilayers alone are stable in air over the same period of time. UV-vis spectroscopy and X-ray photoelectron spectroscopy (XPS) are in agreement with a destruction of the Pc chromophore. This reaction may be initiated by reaction of the anhydride groups of PTCDA with ambient moisture, forming carboxylic acids, as seen by XPS. Control experiments show that PTCDA hydrolyzes in the presence of water and that CllnPc degrades if exposed to acids. These results impact the device implications for long-term use of PTCDA/phthalocyanine assemblies.