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

Tetrapyridotetraazaporphyrinatozinc (TPyTAPZn)can be looked at as a substit uted phthalocyanine. Thin films of TPyTAPZn were prepared on quartz glass b y physical vapour deposition under high-vacuum conditions. During the depos ition, island growth was observed by a characteristic change in the electri cal conduction, indicating an increasing number of conduction pathways alon g the film. Deposition conditions could be optimized to yield an ordered ra ther than amorphous growth as detected by a characteristic absorption band in the visible range, strongly red-shifted from the absorption of the monom eric molecule in solution. A negative Seebeck coefficient confirmed n-type conduction for TPyTAPZn. In temperature-dependent measurements of the elect rical 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 c arrier generation. from this difference it is concluded that a thermally ac tivated charge carrier transport mechanism (hopping) rather than delocalize d conduction (band model) is dominant in TPyTAPZn. Photoconduction turned o ut to be rather small in these samples, although light was absorbed quite e fficiently. The time dependence of photoconduction indicated a significant trap density. Interaction with ammonia or triethylamine in the gas phase le d to an increase in the conductivity; oxygen or water led to a decrease. Th e time dependence of these interactions indicated that triethylamine and wa ter were only reacting with the surface region, whereas NH3 and O-2 were al so diffusing into the bulk of the films. Copyright (C) 1999 John Wiley & So ns, Ltd.