Intermolecular interactions and electrical properties in thin films of tetrapyridotetraazaporphyrinatozinc(II)

✍ Scribed by D. Schlettwein; J. P. Meyer; N. I. Jaeger

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 170 KB
• Volume: 03
• Category: Article
• ISSN: 1088-4246
• DOI: 10.1002/(sici)1099-1409(199908/10)3:6/7<611::aid-jpp184>3.0.co;2-c

✦ Synopsis

Tetrapyridotetraazaporphyrinatozinc (TPyTAPZn)

can be looked at as a substituted phthalocyanine. Thin films of TPyTAPZn were prepared on quartz glass by physical vapour deposition under high-vacuum conditions. During the deposition, island growth was observed by a characteristic change in the electrical conduction, indicating an increasing number of conduction pathways along the film. Deposition conditions could be optimized to yield an ordered rather than amorphous growth as detected by a characteristic absorption band in the visible range, strongly red-shifted from the absorption of the monomeric molecule in solution. A negative Seebeck coefficient confirmed n-type conduction for TPyTAPZn. In temperaturedependent measurements of the electrical conductivity and thermopower across the samples an activation energy of 0.31 eV was established for the conductivity and of 0.04 eV for charge carrier generation. From this difference it is concluded that a thermally activated charge carrier transport mechanism (hopping) rather than delocalized conduction (band model) is dominant in TPyTAPZn. Photoconduction turned out to be rather small in these samples, although light was absorbed quite efficiently. The time dependence of photoconduction indicated a significant trap density. Interaction with ammonia or triethylamine in the gas phase led to an increase in the conductivity; oxygen or water led to a decrease. The time dependence of these interactions indicated that triethylamine and water were only reacting with the surface region, whereas NH 3 and O 2 were also diffusing into the bulk of the films.